Notes - Traffic: Why We Drive the Way We Do - Tom Vanderbilt

Traffic: Why We Drive the Way We Do (and What It Says About Us) - Tom Vanderbilt (2008)


Prologue: Why I Became a Late Merger

in a business magazine: Matt Asay, “How Team Works.” Connect, November 2003. Retrieved from

mingle so freely: There are exceptions to this, of course, as in the case of the ban on women drivers in Saudi Arabia (which extends even to golf carts) or the segregated highways in Israel for Palestinians and Israelis. See Brian Whitaker, “Saudi Driving Ban on Women Extends to Golf Carts,” Guardian, March 3, 2006, and Steven Erlanger, “A Segregated Road in an Already Driving Land,” New York Times, August 11, 2007.

people and things became interchangeable: Sean Dockray, Steve Rowell, and Fiona Whitton point out that while terms like computer and typewriter used to refer to people (e.g., the profession of a typewriter), they now refer exclusively to the technologies themselves. We have become traffic, they argue, but we do not like to admit that in our language. See “Blocking All Lanes,” Cabinet, no. 17 (Spring 2005).

on certain streets altogether: See Eric Poehler, “The Circulation of Traffic in Pompeii’s Regio VI,” Journal of Roman Archaeology, vol. 19 (2005), pp. 53-74.

no traffic or street signs: Poehler argues that given the level of preservation at Pompeii, had these signs existed there would likely be archeological evidence today. Drivers, he suggests, relied instead upon the cues of other drivers or design cues in the streetscape, while people looking for addresses relied more upon relative cues (e.g., turn left at the butcher shop or right at the shrine). Correspondence with Eric Poehler.

Vico di Mercurio: Poehler suggests that these changes must have been overseen by some kind of Department of Traffic Engineering. “The inescapable implication is that the traffic system was carefully managed by a central, executive individual or group at the municipal level.” See Eric Poehler, “A Reexamination of Traffic in Pompeii’s Regio VI: The Casa del Fauno, the Central Baths, and the Reversal of Vico di Mercurio,” Archaeological Institute of America (2005).

In ancient Rome: The Roman traffic history comes from The Roads of the Romans, by Romolo August Staccioli (Rome: L’Erma di Bretschneider, 2003), in particular pp. 21-23.

“a devil-fish from sleeping”: quoted in ibid, p. 23.

“of the Mayor”: The English traffic history comes from the wonderful book Street Life in Medieval England, by G. T. Salusbury Jones (Oxford: Pen-in-Hand, 1939).

“contesting for the way”: The information on traffic fatalities and the accounts of London drivers are taken from Emily Cockayne’s exemplary study Hubbub: Filth, Noise and Stench in England (New Haven: Yale University Press, 2007), pp. 157-80.

“reckless drivers”: The 1867 pedestrian fatality figure comes from Ways of the World: A History of the World’s Roads and of the Vehicles That Used Them (New Brunswick, N.J.: Rutgers University Press, 1992), p. 132.

“wish to pass over”: New York Times, April 9, 1888.

“to show illumination at night”: “Our Unwary Pedestrians,” New York Times, December 24, 1879.

right-of-way to women?: For a delightful account of the impact of the bicycle on American culture, see Sidney H. Aronson, “The Sociology of the Bicycle,” Social Forces, vol. 30, no. 3 (March 1952), pp. 305-12. Aronson noted, “Thus it can be concluded that the bicycle provided a preview on a miniature scale of much of the social phenomena which the automobile enlarged upon.”

“good roads”: For more on the history on the bicycle, including the Good Roads Movement, see David Herlihy’s comprehensive Bicycle: The History (New Haven: Yale University Press, 2005), p. 5. Bicycle manufacturing, Herlihy notes, was the forerunner of the mass assembling of automobiles, and many bicycle-repair shops were converted into gas stations.

“social or business prominence”: New York Times, September 15, 1903.

“right way to turn a corner”: “Proposed Street Traffic Reforms,” New York Times Magazine supplement, February 23, 1902.

“special indications meant”: from Gordon M. Sessions, Traffic Devices: Historical Aspects Thereof (Washington, D.C.: Institute of Traffic Engineers, 1971), p. 63.

“red” time remained: The Wilshire and Western traffic light information comes from Sessions, Traffic Devices, ibid., p. 45.

learned red and green?: The story about color blindness and traffic signals comes from Clay McShane, “The Origins and Globalization of Traffic Control Signals,” Journal of Urban History, March 1999. p. 396.

roles of city streets: Jeffrey Brown, “From Traffic Regulation to Limited Ways: The Effort to Build a Science of Transportation Planning,” Journal of Planning History, vol. 5, no. 1 (February 2006), pp. 3-34.

collapse of the Berlin Wall: For a fascinating discussion of how German Democratic Republic traffic engineering was affected by the reunification of Germany, and the cultural underpinnings and consequences of those decisions, see Mark Duckenfield and Noel Calhoun, “Invasion of the Western Ampelmännchen,German Politics, vol. 6, no. 3 (December 1997), pp. 54-69.

offers no improvement at all: As I was succinctly told by Michael Primeggia, deputy director of operations at New York City’s Department of Transportation, “People have argued that the countdown signal gives more information to peds to make intelligent choices. Why would I think more info would be better, when right now I provide them good information and they choose to ignore it?” Some studies have found that pedestrians were less compliant with countdown signals; see, for example, H. Huang and C. Zegeer, “The Effects of Pedestrian Countdown Signals in Lake Buena Vista,” University of North Carolina Highway Safety Research Center for Florida Department of Transportation, November 2000. Accessible via This could be an artifact, of course, of pedestrians rationally analyzing the situation and deciding that they have plenty of time to cross the street before their signal has expired. While they are technically “violating” the signal, they are also using the information smartly.

gradually rolled back: For a discussion of differential speed limits and their effects on safety, see “Safety Effects of Differential Speed Limits on Rural Interstate Highways,” Federal Highway Administration, Washington, D.C., October 2005, FHWA-HRT-05-042.

“become more surrealistic”: Henry Barnes, The Man with the Red and Green Eyes (New York: Dutton, 1965), p. 218.

“things you can do”: Ralph Vartabadian, “Your Wheels,” Los Angeles Times, May 14, 2003.

“explicit argument”: The quote about convex mirrors comes from a telephone interview with Michael Flannagan.

insurance company surveys: A 2002 survey by Progressive Insurance, for example, which queried more than eleven thousand drivers who had filed a claim for a crash in 2001, found that 52 percent of the accidents occurred within five miles of the driver’s home, and 77 percent occurred within fifteen miles of the home. Retrieved on October 3, 2007, from

A study by: See, for example, Tova Rosenbloom, Amotz Perlmana, and Amit Shahara, “Women Drivers’ Behavior in Well-known Versus Less Familiar Locations,” Journal of Safety Research, vol. 38, issue 3, 2007, pp. 283-88. Studies have also shown drivers are less likely to wear seat belts on shorter trips, which would seem to indicate a feeling of greater safety close to home. See, for one, David W. Eby, Lisa J. Molnar, Lidia P. Kostyniuk, Jean T. Shope, and Linda L. Miller, “Developing an Optimal In-Vehicle Safety Belt Promotion System” (Ann Arbor: University of Michigan Transportation Research Institute, 2004).

food or health care: Driven to Spend (Surface Transportation Policy Project, 2001).

more own three than own one: Alan Pisarski, Commuting in America III (Washington, D.C.,: Transportation Research Board, 2006), p. 38.

has a three-car garage: Amy Orndorff, “Garages Go Gigantic: Car Buffs Opt for Bigger Spaces,” Washington Post, September 13, 2006.

thirty-eight hours annually: See Tim Lomax and David Schrank, 2007 Annual Urban Mobility Report, compiled for the Texas Transportation Institute (College Station: Texas A&M University, 2007).

by nearly half: Surface Transportation Policy Partnership, Mean Streets 2002, chapter 2. Retrieved at

“food and beverage venue”: This phrase comes from Food and Drug Packaging, March 2002.

there were 504: Frozen Food Age, vol. 54, no. 1 (August 2005), p. 38.

84.4 billion in 2008: On-the-go eating figures come from the market research firm Datamonitor.

gentler, slower age: Drive-through sales figure comes from the Wall Street Journal, May 21, 2000.

through a car window: Chicago Sun-Times, October 7, 2005.

at least once per week: According to a survey commissioned by the Food Strategy Implementation Partnership (FSIP), Bord Bia, and Intertrade Ireland, and carried out by Invest NI, as quoted in Checkout, February 2006.

in order to speed traffic: Julie Jargon, “McD’s Aims for the Fast Lane.” Crain’s Chicago Business, June 27, 2005, p. 3. The article does note that the two ordering lanes must merge into one paying lane; there is no word of any reported merging difficulties.

burgeoning drive-through customers: Geoffrey Fowler, “Drive-Through Tips for China,” Wall Street Journal, June 20, 2006.

company-owned stores: Elizabeth M. Gillespie, “Starbucks Bows to Customer Demand,” Toronto Star, December 27, 2005.

“handle well in the car”: This quote comes from a press release accessed through Business Wire, retrieved at The dashboard-dining test was performed by Kelton Research; it was the firm’s CEO, Tom Bernthal, whom I met with to discuss the test.

drive-through window: Carole Paquette, “Drive-Throughs Move Beyond Banks and Fast Food,” New York Times, April 8, 2001.

Audio Publishers Association: Information on audiobooks comes from documents provided by the Audio Publishers Association.

to bear in L.A. traffic: Idan Ivri, “Gridlock: How Traffic Has Rerouted Jewish Life,” Jewish Journal, July 9, 2004. The political scientist Robert Putnam suggests that every ten minutes of commute time “cuts involvement in community affairs by 10 percent” (Putnam’s italics); from Putnam, Bowling Alone: The Collapse and Revival of American Community (New York: Simon and Schuster, 2001), p. 213.

on their left sides: Based on research by Scott Fosko, Saint Louis University School of Medicine. Article retrieved from:

“toward the same horizon”: From Alexis de Tocqueville, Democracy in America (repr.; London: Penguin, 2003), p. 328.

double since 1990: Elizabeth Rosenthal, “Car Boom Puts Europe on Road to a Smoggy Future,” New York Times, January 7, 2007.

underground parking garages: “Car Ownership Boom Means Traffic Jams in Once-Tranquil Tibet,” International Herald Tribune, November 7, 2007.

Caracas: Rory Carroll, “Carbon Leaves Caracas in One Big Jam,” Guardian, November 23, 2006. The “seven cents” gas figure comes from Simon Romero, “Venezuela Hands Narrow Defeat to Chavez Plans,” New York Times,October 30, 2007.

the legendary traffic: In a 2004 estimate, São Paulo was said to have just under four miles of freeways to accommodate more than five million vehicles. Los Angeles, by contrast, had nine hundred miles to handle about seven million vehicles. See Henry Chu, “São Paulo Seeks Road Map to Life Without Traffic Jams,” Los Angeles Times, November 9, 2004. In 2007, a rising number of fatal helicopter crashes was prompting calls to limit the growing airborne traffic. See Cristina Christiano, “SP quer limitar tráfego de helicópteros,” O Globo, September 24, 2007.

faster car-pool lanes: Matthew Moore, “Car Jockeys Often in for Rough Ride from Traffic Police,” Sydney Morning Herald, December 26, 2002.

human “nav system”: This information came via an e-mail correspondence with Jian Shou Wang.

cause of death: World Health Organization. Retrived from:

Chapter One: Why Does the Other Lane Always Seem Faster?

“modal bias”: This term was suggested to me in a conversation with Aaron Naparstek.

“change of mode”: Hélène Fontaine and Yves Gourlet, “Fatal Pedestrian Accidents in France: A Typological Analysis,” Accident Analysis and Prevention, vol. 39, no. 3 (1997), pp. 303-12.

“drives as he lives”: W. A. Tillman and G. E. Hobbs, “The Accident-Prone Automobile Driver: A Study of the Psychiatric and Social Background,” American Journal of Psychiatry, vol. 106 (November 1949), pp. 321-31. Many of us may think of “road rage” as a rather new concept, like “air rage” or “surfing rage,” but it is really as old as the automobile itself. The year 1968, for example, might have been marked by violent social upheaval in metropolises from Paris to Mexico City, but there was another form of violence in the air: That year, Mayer H. Parry published Aggression on the Road, while the New York Times reported on government testimony about “uncontrollable violent behavior” on the nation’s roads. (Three years later, F. A. Whitlock followed up with his book Death on the Road: A Study in Social Violence.) See John D. Morris, “Driver Violence Tied to Crashes,” New York Times,March 2, 1968.

risks on the road: For a discussion, see Patrick L. Brockett and Linda L. Golden, “Biological and Psychobehavioral Correlates of Credit Scores and Automobile Insurance Losses: Toward an Explication of Why Credit Scoring Works,” Journal of Risk and Insurance, vol. 1, no. 74 (March 2007), pp. 23-63.

typically involve questionnaires: See, for example, David L. Van Rooy, James Rotton, and Tina M. Burns, “Convergent, Discriminant, and Predictive Validity of Aggressive Driving Inventories: They Drive as They Live,” Aggressive Behavior, vol. 3, no. 2 (February 2006), pp. 89-98.

more aggressive manner: This is a virtual consensus in the field, as demonstrated by a survey of the scholarly literature in B. A. Jonah, “Sensation Seeking and Risky Driving: A Review and Synthesis of the Literature,” Accident Analysis and Prevention, vol. 29, no. 5 (1997), pp. 651-65.

“Traffic tantrums”: Thanks to Ian Walker for this phrase.

especially by novice drivers: Kazumi Renge, “Effect of Driving Experience on Drivers’ Decoding Process of Roadway Interpersonal Communication,” Ergonomics, vol. 43, no. 1 (1 January 2000), pp. 27-39.

Green Day bumper sticker: This brings up the point of whether there should really be any nonessential communication in traffic at all. As the German sociologist Norbert Schmidt-Relenberg has observed, “It could be said that cooperation in traffic is not a means to attain something positive, but to avoid something negative: every participant in the system attempts to attain his destination without friction. Hence traffic is a system all its own; the less its participants come into contact with each other and are compelled to interaction, the better it works: a system defined and approved in the reality by a principle of minimized contact.” In other words, not only should we not honk at people with Green Day stickers, we should not put the sticker there in the first place. Norbert Schmidt-Relenberg, “On the Sociology of Car Traffic in Towns,” in Transport Sociology: Social Aspects of Transport Planning, ed. Enne de Boer (Oxford, New York: Pergamon Press, 1986), p. 122.

violated traffic laws: María Cristina Caballero, “Academic Turns City into a Social Experiment,” Harvard University Gazette, March 11, 2004.

associated with subordination: Katz suggests this may be why we so often call other drivers “assholes” and give the “up yours” finger.

by the honker: Andrew R. McGarva and Michelle Steiner, “Provoked Driver Aggression and Status: A Field Study,” Transportation Research F: Psychology and Behavior, vol. 167 (2000), pp. 167-179.

anything but rude or hostile: What if our signals were more meaningful? A few years ago, before the Tokyo Motor Show, Simon Humphries, a designer for Lexus in Japan, told me in an e-mail exchange that the Toyota Motor Company had proposed a car—nicknamed POD—that would contain a “vehicle expression operation control system.” Accompanying the usual lights and arrows would be a new range of signals. The headlights would be “anthropomorphized” with “eyes” and “eyebrows,” the antenna would “wag,” and different colors would be used to show emotion. “As traffic grows heavier and vehicle use increases,” reads the U.S. patent application, “vehicles having expression functions, such as crying or laughing, like people and other animals do, could create a joyful, organic atmosphere rather than the simple comings and goings of inorganic vehicles.” Indeed, a German company even released an aftermarket version of this system, called Flashbox, that uses a series of blinks to signify things like “apology,” “annoyed,” and “stop for more?” Adding signals, however, creates many new problems. Everyone has to learn the new signals. More information in traffic means more time to process. The receiver of a “smile,” moreover, may not understand why they have received it any more so than a honk. And flashing “angry” signals may provoke rather than defuse violence.

deficient male anatomy: One male Australian driver was actually fined because when a woman wagged her pinkie at him, he responded by hurling a plastic bottle at her windshield. The man claimed that the gesture was akin to a “sexual assault,” a worse insult than the traditional finger. “The ‘finger,’ it’s so common now, that we’re over it, but this finger is a whole new thing and it’s been promoted so much everybody knows it and you just get offended,” he said. David Brouithwaite, “Driver Points to Ad Campaign for His Digitally Enhanced Road Rage,” The Sydney Morning Herald, November 1, 2007.

“constructing moral dramas”: For a more detailed discussion of Katz’s investigation of anger in traffic, see Jack Katz, How Emotions Work (Chicago: University of Chicago Press, 1999), in particular the first chapter, “Pissed Off in L.A.”

“the angry driver”: Jack Katz, How Emotions Work, p. 48.

“actor-observer effect”: See L. D. Ross, “The Intuitive Psychologist and His Shortcomings: Distortions in the Attribution Process,” in Advances in Experimental Social Psychology, vol. 10, ed. L. Berkowitz (New York: Random House, 1977), pp. 173-220.

feel more in control: As Thomas Britt and Michael Garrity write, “individuals will probably err in the direction of assuming an internal locus of causality for the offending driver’s behavior in order to feel some sense of control over events when driving.” “Attributions and Personality as Predictors of the Road Rage Response,” British Journal of Social Psychology, vol. 45 (2006), pp. 127-47.

required by the circumstances: This was the finding arrived at when a group of researchers for England’s Transport Research Laboratory conducted a series of interviews with drivers, part of which included assessments of cyclist and driver behavior in traffic scenarios. They concluded, “The underlying unpredictability of cyclists’ behavior was seen by drivers as stemming from the attitudes and limited competence of the cyclists themselves, rather than from the difficulty of the situations that cyclists are often forced to face on the road (i.e., drivers made a dispositional rather than a situational attribution). Despite their own evident difficulties in knowing how to respond, drivers never attributed these difficulties to their own attitudes or competencies, nor did they do so in relation to other drivers (i.e. they made a situational attribution about their own and other drivers’ behavior). This pattern of assignment of responsibility is characteristic of how people perceive the behavior of those they consider to be part of the same social group as themselves, versus those seen as part of a different social group.” L. Basford, D. Davies, J. A. Thomson, and A. K. Tolmie, “Drivers’ Perception of Cyclists,” in TRL Report 549: Phase I—a Qualitative Study (Crowthorne: Transport Research Laboratory, 2002).

shares their birth date: See D. T. Miller, J. S. Downs, and D. A. Prentice, “Minimal Conditions for the Creation of a Unit Relationship: The Social Bond Between Birthday Mates,” European Journal of Social Psychology, vol. 28 (1998), pp. 475-81. This idea was raised in an interesting paper by James W. Jenness, “Supporting Highway Safety Culture by Addressing Anonymity,” AAA Foundation for Traffic Safety, 2007.

Katz says, cyborgs: This point was made as early as 1930, by a city planner in California who suggested that “Southern Californians have added wheels to their anatomy.” The quote comes from J. Flink, The Automobile Age(Cambridge, Mass: MIT Press, 1988), p. 143, via an excellent article by John Urry, a sociologist at Lancaster University. See John Urry, “Inhabiting the Car,” published by the Department of Sociology, Lancaster University, Lancaster, United Kingdom, available at

different people: See Henrik Walter, Sandra C. Vetter, Jo Grothe, Arthur P. Wunderlich, Stefan Hahn, and Manfred Spitzer, “The Neural Correlates of Driving,” Brain Imaging, vol. 12, no. 8 (June 13, 2001), pp. 1763-67.

and following distance: See David Shinar and Richard Compton, “Aggressive Driving: An Observational Study of Driver, Vehicle and Situational Variables,” Accident Analysis & Prevention, vol. 36 (2004), pp. 429-37.

give themselves over to the car: Research also suggests that single drivers are more susceptible to fatigue and being involved in crashes, and it is not difficult to speculate why. Passengers provide another “set of eyes” to warn of potential hazards and can aid in keeping the driver engaged. For the increased risk factors to single drivers see, for example, Vicki L. Neale, Thomas A. Dingus, Jeremy Sudweeks, and Michael Goodman, “An Overview of the 100-Car Naturalistic Study and Findings.” National Highway Traffic Safety Administration, Paper Number 05-0400.

thirty-three citations: See F. K. Heussenstamm, “Bumper Stickers and the Cops,” Trans-Action (Society), vol. 8 (February 1971), pp. 32 and 33. The author acknowledged that the subjects’ driving may have been affected by the experiment itself but argued that “it is statistically unlikely that this number of previously ‘safe’ drivers could amass such a collection of tickets without assuming real bias by police against drivers with Black Panther bumper stickers.” The information about specially designated license plates comes from “New ‘Scarlet Letter’ for Predators in Ohio,” Associated Press, March 1, 2007. The license plates raise, ironically, a problem similar to “Children at Play” signs: They signify that a car without such plates is somehow safe for children to approach, just as the “Children at Play” signs suggest that drivers can act less cautiously in areas without the signs.

aggressive driving on her part: Women driving SUVs, as at least one set of very limited observational studies found, drove faster in 20-mile-per-hour school zones, parked more often in restricted shopping mall fire zones, came to a stop less frequently at stop signs, and were slower to move through an intersection when the light turned green, as compared to other drivers in other types of vehicles. As the author himself admits, the sample sizes were small, and the higher rates of women SUV drivers may simply have reflected the fact that the study took place in a setting where there happened to be a higher than average number of women driving SUVs. See John Trinkaus, “Shopping Center Fire Zone Parking Violators: An Informal Look,” Perceptual and Motor Skills, vol. 95 (2002), pp. 1215-16; John Trinkaus, “School Zone Speed Limit Dissenters: An Informal Look,” Perceptual and Motor Skills, vol. 88 (1999), pp. 1057-58.

at greater risk: See, for example, Devon E. Lefler and Hampton C. Gabler, “The Fatality and Injury Risk of Light Truck Impacts with Pedestrians in the United States,” Accident Analysis & Prevention, vol. 36 (2004), pp. 295-304.

“grieving while driving”: Paul C. Rosenblatt, “Grieving While Driving,” Death Studies, vol. 28, (2004), pp. 679-86.

including nasal probing: Thanks to Daniel McGehee for this story.

not wearing hoods: Philip Zimbardo. “The Human Choice: Individuation, Reason, and Order vs. Deindividuation, Impulse, and Chaos.” In Nebraska Symposium on Motivation, ed. W. J. Arnold and D. Levine (Lincoln: University of Nebraska Press, 1970). Zimbardo’s description of the conditions that contribute to the sense of “deindividuation” are worth noting in light of traffic. He writes: “Anonymity, diffused responsibility, group activity, altered temporal perspective, emotional arousal, and sensory overload are some of the input variables that can generate deindividuated reactions.” Arguably, all of Zimbardo’s “input variables” can routinely be found in traffic situations. The quote comes from Zimbardo’s “Depersonalization” entry in International Encyclopedia of Psychiatry, Psychology, Psychoanalysis, and Neurology, vol. 4, ed. B. B. Wolman (New York: Human Sciences Press, 1978), p. 52.

to the executioners: The hostage and firing squad information comes from David Grossman, On Killing: The Psychological Cost of Learning to Kill in War and Society (Boston: Back Bay Books, 1996), p. 128.

with the tops up: Patricia A. Ellison, John M. Govern, Herbert L. Petri, Michael H. Figler, “Anonymity and Aggressive Driving Behavior: A Field Study,” Journal of Social Behavior and Personality, vol. 10, no. 1 (1995), pp. 265-72.

“online disinhibition effect”: See J. Suler, “The Online Disinhibation Effect,” CyberPsychology and Behavior, vol. 7 (2004), pp. 321-26.

relatively large social networks: See, for example, R. I. M. Dunbar, “Neocortical Size as a Constraint on Group Size in Primates,” Journal of Human Evolution, vol. 22 (1993), pp. 469-93.

higher testosterone levels: Roxanne Khamsi, “Hormones Affect Men’s Sense of Fair Play,” New Scientist, July 4, 2007.

“strong reciprocity”: See Ernst Fehr, Urs Fischbacher, and Simon Gächter, “Strong Reciprocity, Human Cooperation and the Enforcement of Social Norms,” Human Nature, vol. 13 (2002), pp. 1-25.

altruistic all the same: The comments on road rage from Herbert Gintis come from an interview posted at The example of the bird signaling a predator’s approach comes from Olivia Judson, “The Selfish Gene,” Atlantic Monthly, October 2007, p. 92. It has also been speculated that animals raising an alarm against a predator are actually sending a signal to the predator that it has been spotted. For an interesting theoretical discussion, see C. T. Bergstrom and M. Lachmann, “Alarm Calls as Costly Signals of Antipredator Vigilance: The Watchful Babbler Game,” Animal Behaviour, vol. 61 (2001), pp. 535-43.

around 20 miles per hour: Ben Hamilton-Baillie, “Improving Traffic Behaviour and Safety Through Urban Design,” Civil Engineering, vol. 158 (May 2005), pp. 39-47.

result was the same: P. C. Ellsworth, J. M. Carlsmith, and A. Henson, “The Stare as a Stimulus to Flight in Human Subjects: A Series of Field Experiments,” Journal of Personality and Social Psychology, vol. 21 (1972), pp. 302-11.

were not present: Kevin J. Haley and Daniel M. T. Fessler, “Nobody’s Watching? Subtle Cues Affect Generosity in an Anonymous Economic Game,” Evolution and Human Behavior, vol. 26 (2005), pp. 245-56.

university break room: See Melissa Bateson, Daniel Nettle, and Gilbert Roberts, “Cues of Being Watched Enhance Cooperation in a Real-World Setting,” Biology Letters, June 2, 2006.

cooperation in humans: Michael Tomasello, Brian Hare, Hagen Lehmann, and Josep Call, “Reliance on Head Versus Eyes in the Gaze Following of Great Apes and Human Infants: The Cooperative Eye Hypothesis,” Journal of Human Evolution, vol. 52 (2007), pp. 314-20.

direction of one’s gaze: Smiling might help as well, at least if you’re female and the person you’re smiling at is male, a French study showed. The study had male and female subjects try to hitch rides by smiling or not smiling at passing drivers. More women received rides when they smiled, but for men, alas, this did not work. Also, every driver that stopped was male. Nicolas Guegue and Jacques Fischer-Lokou, “Hitchhikers’ Smiles and Receipt of Help,” Psychological Reports, vol. 94, (2004), pp. 756-60.

tilt your head up: Michael Tomasello, Brian Harea, Hagen Lehmanna, and Josep Call, “Reliance on Head Versus Eyes in the Gaze Following of Great Apes and Human Infants: The Cooperative Eye Hypothesis,” Journal of Human Evolution, vol. 52, no. 3 (March 2007), pp. 314-20.

if one does not make eye contact: Robert Wright explains this phenomenon succinctly: “When we pass a homeless person, we may feel uncomfortable about failing to help. But what really gets the conscience twinging is making eye contact and still failing to help. We don’t seem to mind not giving nearly so much as we mind being seen not giving.” (As for why we should care about the opinion of someone we’ll never encounter again: Perhaps in our ancestral environment, just about everyone encountered was someone we might well encounter again.) From The Moral Animal (New York: Alfred A. Knopf, 1994), p. 206.

“if there are more than two”: Thomas Schelling, Choice and Consequence (Cambridge, Mass.: Harvard University Press, 1984), p. 214.

first through the intersection: Schelling also suggested throwing one’s steering wheel out the window as a sign that one has committed to one’s course of action.

at the oncoming car: A. Katz, D. Zaidel, and A. Elgrishi. “An Experimental Study of Driver and Pedestrian Interaction During the Crossing Conflict,” Human Factors, vol. 17, no. 5 (1975), pp. 514-27.

Or was it just chivalry?: Jeffrey Z. Rubin, Bruce D. Steinberg, and John R. Gerrein, “How to Obtain the Right of Way: An Experimental Analysis of Behavior at Intersections,” Perceptual and Motor Skills, vol. 34 (1974), pp. 1263-74.

in New York City: Of course, the faster pace of life in New York City also has an affect on the traffic culture. Michael Primeggia, the deputy director of the New York City Department of Transportation, told me the following joke: “What’s the shortest amount of recorded time? The time between the light turning green in New York and the horn sounding.”

visibly express anger: Andrew R. McGarva, Matthew Ramsey, and Suzannah A. Shear, “Effects of Driver Cell-Phone Use on Driver Aggression,” Journal of Social Psychology, vol. 146, no. 2 (2006), pp. 133-46.

replicated in Australia: S. Bochner, “Inhibition of Horn-Sounding as a Function of Frustrator’s Status and Sex: An Australian Replication and Extension of Doob and Gross,” Australian Journal of Psychology, vol. 6 (1968), pp. 194-99.

doing the blocking: A. N. Doob and A. E. Gross, “Status of Frustrator as an Inhibitor of Horn-Honking Responses,” Journal of Social Psychology, vol. 76 (1968), pp. 213-18.

you guessed right: Andreas Diekmann, Monika Jungbauer-Gans, Heinz Krassnig, Heinz Lorenz, and Sigrid Lorenz, “Social Status and Aggression: A Field Study Analyzed by Survival Analysis,” Journal of Social Psychology; vol. 136, no. 6 (December 1996), pp. 761-68.

been at work: See Ben Jann, “Driver Aggression as a Function of Status Concurrence: An Analysis of Horn-Honking Responses,” Bern, Switzerland, 2002; available at Interestingly, this study found, as in the earlier mentioned birthday study, that drivers of a vehicle were less likely to honk at a vehicle when it was of the same status. The researcher noted, however, that “our data do not reveal whether it is actually similaritywhich reduces aggression or rather difference that increases it.”

when it was a man: Kay Deux, “Honking at the Intersection: A Replication and Extension,” Journal of Social Psychology, vol. 84 (1971), pp. 159-60.

a driving “lesson”: H. Yazawa, “Effects of Inferred Social Status and a Beginning Driver’s Sticker upon Aggression of Drivers in Japan,” Psychological Reports, vol. 94 (2004), pp. 1215-20.

from another country: The study, interestingly, found that French, Spanish, and Italian drivers were faster to the horn than German drivers (Italians were the fastest). Drivers also honked more when the visible sticker was German and not the less recognizable Australian identity sticker. See Joseph P. Forgas, “An Unobtrusive Study of Reactions to National Stereotypes in Four European Countries,” Journal of Social Psychology, vol. 99 (1976), pp. 37-42.

suspected these things: Drivers, of course, may simply be honking in a “nonaggressive” way simply to let the driver ahead know that the light has changed. But as Dwight Hennessey has pointed out, the frequency and latency of honks indicates that more than just polite signaling is at work. See Dwight Hennessey, “The Interaction of Person and Situation Within the Driving Environment: Daily Hassles, Traffic Congestion, Driver Stress, Aggression, Vengeance and Past Performance” (Ph.D. dissertation, York University, Toronto, Ontario, April 1999).

In another study: Ian Walker, “Signals Are Informative but Slow Down Responses When Drivers Meet Bicyclists at Road Junctions,” Accident Analysis & Prevention, vol. 37 (2005), pp. 1074-85.

In a previous study: Ian Walker, “Road Users’ Perceptions of Other Road Users: Do Different Transport Modes Invoke Qualitatively Different Concepts in Observers?” Advances in Transportation Studies, section A, no. 6 (2005), pp. 25-32.

rendered invisible by the car: Perhaps the subjects were distracted by simply recognizing the make and model of car. Psychologists at Vanderbilt University have shown in clinical tests that car aficionados shown pictures of cars were less able to identify faces at the same time. Car fanciers were looking at cars as if they were faces, causing a “perceptual traffic jam” in a part of the brain implicated in the “holistic” visual processes of facial recognition. See Isabel Gauthier and Kim M. Curby, “A Perceptual Traffic Jam on Highway N170: Interference Between Face and Car Expertise,” Current Directions in Psychological Science, vol. 14, no. 1 (February 2005), pp. 30-33.

people’s eyes meet: See, for example, A. Gale, G. Spratt, AJ Chapman, and A. Smallbone, “EEG correlates of eye contact and interpersonal distance,” Biological Psychology, vol. 3, no. 4 (December 1975), pp. 237-45.

to the actual road: For further details on the study, see Ian Walker, “Drivers Overtaking Bicyclists: Objective Data on the Effects of Riding Position, Helmet Use, Vehicle Types and Apparent Gender,” Accident Analysis & Prevention, vol. 39 (2007), pp. 417-25.

the driver slows: There is conceivably no limit to the number and variety of stereotypes drivers possess about other vehicles and the people driving them—for example, BMW drivers are aggressive, minivan drivers are slow. How all these secret interactions all play out in traffic is virtually beyond study. Do certain car drivers act a certain way, and do we act differently toward certain cars or drivers? Do you get the finger in a Hummer and a cute smile in a Mini, and does this then affect the way you drive, which then reinforces the stereotype? Research has suggested one drawback of these stereotypes: When subjects were read the description of a crash between two cars in which the actual facts were unknown, they estimated that the speed of one car was higher when the driver was younger and in a stereotypical “boy racer” car. (The effect was even stronger when the color was red!) See Graham M. Davies and Darshana Patel, “The Influence of Car and Driver Stereotypes on Attributions of Vehicle Speed, Position on the Road and Culpability in a Road Accident Scenario,” Legal and Criminal Psychology, vol. 10, (2005), pp. 45-62.

automatic reponses: Irene V. Blaire and Mahzarin R. Banaji, “Automatic and Controlled Processes in Stereotype Priming,” Journal of Personality and Social Psychology, vol. 70, no. 6 (1996), pp. 1142-63.

waiting in line: See David Maister, “The Psychology of Waiting in Line,” available at

on the highway itself: L., Zhang, F. Xie, and D. Levinson, “Variation of the Subjective Value of Travel Time Under Different Driving Conditions.” Paper presented at the Eighty-four Transportation Research Board Annual Meeting, January 9-13, 2005, Washington, D.C.

groups often move faster: See David A. Hensher, “Influence of Vehicle Occupancy on the Valuation of Car Driver’s Travel Time Savings: Identifying Important Behavioural Segments,” Working Paper ITLS-WP-06-011, May 2006, Institute of Transport and Logistics Studies, University of Sydney.

with our perception of time: A curious example of this are the new “smart” elevator systems being installed in high-rise buildings around the world. Instead of simply calling an elevator, users are grouped according to which floor they want. In theory, this speeds up the average journey by 50 percent, but it also prompts impatience in people who see elevators bound for other floors arriving and leaving before theirs; they think they are actually waiting longer. See Clive Thompson, “Smart Elevators,” New York Times, December 10, 2006.

“At least I’m better off than you”: See Rongrong Zhou and Dilip Soman, “Looking Back: Exploring the Psychology of Queuing and the Effect of the Number of People Behind,” Journal of Consumer Research, vol. 29 (March 2003).

“irritated with that”: On the differences in queue systems between Wendy’s and McDonald’s, there is another factor to consider: customers’ perceptions of the length of the line. McDonald’s says that people will renege on a line that looks longer; hence it prefers shorter multiple lines, despite Wendy’s claims that a single line is faster. See “Merchants Mull the Long and Short of Lines,” Wall Street Journal, September 3, 1998.

an eighty-minute drive: The lane-changing experiment was conducted by the CBC’s Fifth Estate. Details are available at

did passing them: Donald A. Redelmeier and Robert J. Tibshirani, “Why Cars in the Next Lane Seem to Go Faster,” Nature, vol. 35, September 2, 1999.

at the forward roadway: See, for example, Alexei R. Tsyganov, Randy B. Machemehl, Nicholas M. Warrenchuk, and Yue Wang, “Before-After Comparison of Edgeline Effects on Rural Two-Lane Highways,” Report No. FHWA/TX-07/0-50902 (Austin: Center for Transportation Research, University of Texas at Austin, 2006).

stay in our lane: See, for example, D. Salvucci, A. Liu, and E. R. Boer, “Control and Monitoring During Lane Changes,” in Vision in Vehicles: 9, conference proceedings (Brisbane, Australia, 2001).

looking in the rearview mirror: The forward and rearview percentages are drawn from M. A. Brackstone and B. J. Waterson, “Are We Looking Where We Are Going? An Exploratory Examination of Eye Movement in High Speed Driving.” Paper 04-2602, Proceedings of the 83rd Annual Meeting of the Transportation Research Board (Washington D.C., January 2004).

“loss aversion”: The notion of loss aversion was first hypothesized by Daniel Kahneman and Amos Tversky, “Prospect Theory: An Analysis of Decision Under Risk,” Econometrica, vol. 47 (1979), pp. 263-91.

sensitive to loss: See Sabrina M. Tom, Craig R. Fox, Christopher Trepel, and Russell A. Poldrack, “The Neural Basis of Loss Aversion in Decision-Making Under Risk,” Science, vol. 315, no. 5811 (26 January 2007), pp. 515-18. See also William J. Gehring and Adrian R. Willoughby, “The Medial Frontal Cortex and the Rapid Processing of Monetary Gains and Losses,” Science, vol. 295, no. 5563 (2002), pp. 2279-82.

“endowment effect”: D. Kanheman, J. L. Knetsch, and R. H. Thaler, “Experimental Tests of the Endowment Effect and the Coase Theorem,” Journal of Political Economy, vol. 98 (1990) pp. 1325-48.

to the person leaving it: The parking lot studies were chronicled in R. Barry Ruback and Daniel Juieng, “Territorial Defense in Parking Lots: Retaliation Against Waiting Drivers,” Journal of Applied Social Psychology, vol. 27, no. 9 (1997), pp. 821-34. The authors suggest another theory: that fighting for the “symbolic value” of the parking space when it is threatened by an intruder helps give the parking spot owner a feeling of heightened control over the situation. This is why, they suggest, people will take even longer to vacate a spot when the waiting driver honks. It is a threat to their “sense of freedom,” and the best response is to simply stay longer in the parking space, thus asserting that sense of freedom.

involved lane changes: Basav Sen, John D. Smith, and Wassim G. Najm, “Analysis of Lane Change Crashes,” DOT-VNTSC-NHTSA-02-03, National Highway Traffic Safety Administration, March 2003.

how many were discretionary?: One study that compared crashes to traffic volume (obtained via loop-inductor data) found that most lane-change crashes occurred, perhaps not surprisingly, when the variability of highway speeds across lanes was highest—in other words, the time when most people would find it advantageous to change lanes. See Thomas F. Golob, Wilfred W. Recker, and Veronica M. Alvarez, “Freeway Safety as a Function of Traffic Flow,” Accident Analysis & Prevention, vol. 36 (2004), pp. 933-46.

decisions we make while driving: At Cooper University Hospital in New Jersey, for example, doctors estimate that 60 percent of the trauma intensive care unit patients are the victims of car crashes; see Geoff Mulvihill, “In Corzine’s Hospital Unit, Handling Terrible Accidents Routine,” Newsday, April 23, 2007.

work zones: The work-zone fatality statistic comes from the U.S. Federal Highway Administration (

“merging difficulties”: From Understanding Road Rage: Implementation Plan for Promising Mitigation Measures, by Carol H. Walters and Scott A. Cooner (Texas Transportation Institute, November 2001).

lane that will close: Information on work-zone merge strategies was drawn from a number of useful sources, including “Dynamic Late Merge Control Concept for Work Zones on Rural Freeways,” by Patrick T. McCoy and Geza Pesti, Department of Civil Engineering, University of Nebraska.

smoothly through the work zone: The TRL data comes from a report by G. A. Coe, I. J. Burrow, and J. E. Collins, “Trials of ‘Merge in Turn’ Signs at Major Roadworks.” Unpublished project report, PR/TT/043/95, N207, October 30, 1997.

exactly where to merge: For a sample discussion of U.K. merging ambiguity, see Retrieved on December 1, 2007.

which is also safer: See Federal Highway Administration, U.S. Department of Transportation, “Methods and Procedures to Reduce Motorist Delays in European Work Zones,” FHWA-PL-00-001, October 2000.

One important caveat: Another simulation study showed that the Late Merge strategy was more effective when two lanes narrowed to one than when three narrowed to two. According to one report, “A possible explanation may be evident in the way vehicles appeared to be behaving in the simulations. When simulation animations of the 3-to-2 lane configurations of the late merge control were viewed, it appeared that vehicles driving in the middle lane would move to the far left lane to avoid merging from the closing lane. This interaction slowed vehicles in the far left lane enough that throughput may have been significantly reduced.” Evaluation of the Late Merge Workzone Traffic Control Strategy, by Andrew G. Beacher, Michael D. Fontaine, and Nicholas J. Garber. Virginia Transportation Research Council, August 2004, VTRC 05—R6.

summer of 2003: The Minnesota Dynamic Late Merge information was drawn from two reports, “Dynamic Late Merge System Evaluation: Initial Deployment on I-10,” prepared by URS for the Minnesota Department of Transportation,” and a follow-up study, “Evaluation of 2004 Dynamic Late Merge System for the Minnesota Department of Transportation,” also prepared by URS.

blocked by trucks: Garber, in a telephone conversation, also noted the particular tendency of trucks to perform blocking maneuvers. He found that Late Merge worked best when the total volume of heavy vehicles in the traffic stream was less than 20 percent.

Chapter Two: You’re Not as Good a Driver as You Think You Are

fifteen hundred “subskills”: This estimate comes from A. J. McKnight and B. Adams, Driver Education Task Analysis, vol. 1, Task Descriptions, Washington D.C.: National Highway Traffic Safety Administration, 1970.

twenty per mile: Leslie George Norman, “Road Traffic Accidents: Epidemiology, Control and Prevention” (World Health Organization, Public Health Papers no. 12, 1962), p. 51.

440 words, per minute: This figure comes from William Ewald, Street Graphics (Washington, D.C.: American Society of Landscape Architects Foundation), p. 32.

“avoiding obstacles”: See Urban Challenge Rules (Arlington, Va.: Defense Advanced Research Projects Agency, July 10, 2007).

in the future: The cognitive scientist Donald D. Hoffman points out that an average traffic scene of a tree-lined street with cars creates a multitude of problems for computer intelligence, as analysis by researcher Scott Richman has revealed. Hoffman notes, “Several problems that Richman faced are evident from this picture: clutter, trees moving in the wind, shadows dancing on the road, cars in front hiding cars behind. A sophisticated analysis of motion, using several frames of motion at once, allows Richman’s system to distinguish the motion of cars from that of trees and shadows…. [Richman’s] system can trackcars through shadows, a feat that is trivial for our visual intelligence but, heretofore, quite difficult for computer vision systems. It’s easy to underestimate our sophistication at constructing visual motion. That is, until we try to duplicate that sophistication on a computer. Then it seems impossible to overestimate it.” From Donald D. Hoffman, Visual Intelligence (New York: W. W. Nortion, 1998), p. 170.

“caution for the caution”: See, for example, Don Leavitt, “Insights at the Intersection,” Traffic Management and Engineering, October 2003.

sooner than necessary: H. Kölla, M. Badera, and K. W. Axhausen, “Driver Behavior During Flashing Green Before Amber: A Comparative Study,” Accident Analysis & Prevention, vol. 36, no. 2 (March 2004), pp. 273-80.

without the flashing green: D. Mahalel and D. M. Zaidel, “Safety Evaluation of a Flashing Green Light in a Traffic Signal,” Traffic Engineering and Control, vol. 26, no. 2 (1985), pp. 79-81.

chances to crash: This point is made in L. Staplin, K. W. Gish, L. E. Decina, K. H. Lococo, D. L. Harkey, M. S. Tarawneh, R. Lyles, D. Mace, and P. Garvey in Synthesis of Human Factors Research on Older Drivers and Highway Safety, vol. 2, Publication No. FHWA-RD-97-095, 1997. Available at

“bump itself up the queue”: One might think that robot drivers would be free from the complicated psychological dynamics that trouble humans at intersections; yet, perhaps like humans, it all depends on how they are wired. “Robots can be more aggressive or more conservative,” Montemerlo told me. You might, for example, “program your robot to always ignore the queuing order and always go first, to be a pushy robot.” But whether or not this strategy works depends on how the other robots have been programmed. Four pushy robots at a four-way stop could get ugly quickly.

“They slow everyone down”: This recalls a comment from T. C. Willet’s Criminal on the Road: A Study of Serious Motoring Offences and Those Who Commit Them (London: Tavistock Publications, 1964). As Willet noted: “Some years ago a contest was arranged between two cars to be driven across a city area. One driver had to observe all signs, traffic lights, and speed regulations. The other was allowed to ignore all three if he could do so without endangering the lives of other road users. The law-breaking motorist arrived at this destination just—and only just—ahead of his law-abiding antagonist” (p. 129).

“without a hitch”: The eBay quote comes from Theresa Howard, “Ads Pump up eBay Community with Good Feelings,” USA Today, October 17, 2004.

more in revenue: Paul Resnick, Richard Zeckhauser, John Swanson, and Kate Lockwood, “The Value of Reputation on eBay: A Controlled Experiment.” John F. Kennedy School of Government, Harvard University; Working Paper No. RWP03-007.

(provided it’s authentic): See, for example, John Morgan and Jennifer Brown, “Reputation in Online Auctions: The Market for Trust,” California Management Review, Fall 2006. About 98 percent of feedback on eBay is positive, which has led economist Axel Ockenfels of the University of Cologne in Germany to suspect that people may be afraid of negative retaliatory feedback. Ockenfels has worked with eBay to introduce mechanisms that allow users to post honest, negative feedback with less fear of reprisal. See Christoph Uhlhaas, “Is Greed Good?” Scientific American Mind, August-September 2007, p. 67.

“rising insurance premiums”: Lior J. Strahilevitz, “How’s My Driving? For Everyone (and Everything?),” Public Law and Legal Theory Working Paper No. 125, Law School, University of Chicago. Accessed from

have been tried: The Web site, for example, posts pictures of New York City cars with various official parking permits that are nonetheless parked illegally (many cars also have bootleg parking permits).

actual driving record: C. E. Preston and S. Harris, “Psychology of Drivers in Traffic Accidents,” Journal of Applied Psychology, vol. 49 (1965), pp. 284-88.

they were “better”: For a good summary of these studies, see D. Walton and J. Bathurst, “An Exploration of the Perceptions of the Average Driver’s Speed Compared with Perceived Driver Safety and Driving Skill,” Accident Analysis & Prevention, vol. 30 (1998), 821-30.

most dangerous thing: John Groeger, a psychologist at the University of Surrey in England, points out that this behavior may be a way to “protect ourselves from the anxieties involved in constantly placing ourselves at risk by developing confidence in our ability which we are rarely likely to be forced to realize is misplaced.” See Groeger, Understanding Driving (East Sussex: Psychology Press, 2001), p. 163.

smallest returns: Brad M. Barber and Terrance Odean, “Trading Is Hazardous to Your Wealth: The Common Stock Investment Performance of Individual Investors,” Journal of Finance, vol. 55, no. 2 (2000).

car accident: Julie M. Kos and Valerie A. Clarke, “Is Optimistic Bias Influenced by Control or Delay?” Health Education Research: Theory and Practice, vol. 16, no. 5 (2001), pp 533-40.

have done it: The texting while driving poll comes from Reuters, August 7, 2007. Retrieved from

underestimate our own risk: For an interesting discussion of this phenomenon in the context of seat-belt usage, see “Unconscious Motivators and Situational Safety Belt Use,” Traffic Safety Facts: Traffic Tech, No. 315 (Washington, D.C.: National Highway Traffic Safety Administration, 2007).

social mores and traffic laws: For a seminal discussion of these problems, see H. Laurence Ross, “Traffic Law Violation: A Folk Crime,” Social Problems, vol. 8, no. 3 (1960-61) pp. 231-41.

in question are ambiguous: See R. B. Felson, “Ambiguity and Bias in the Self-Concept,” Social Psychology Quarterly, vol. 44 (March 1981), pp. 64-69.

“unskilled and unaware of it”: Justin Kruger and David Dunning, “Unskilled and Unaware of It: How Difficulties in Recognizing One’s Own Incompetence Lead to Inflated Self-Assessments,” Journal of Personality and Social Pscyhology, vol. 77, no. 6, (1999), pp. 1121-34.

“better” (i.e., safer) drivers: E. Kunkel, “On the Relationship Between Estimate of Ability and Driver Qualification,” Psychologie und Praxis, vol. 15 (1971), pp. 73-80.

(particularly men): See Frank P. McKenna, Robert A. Stanier, and Clive Lewis, “Factors Underlying Illusory Self-Assessment of Driving Skill in Males and Females,” Accident Analysis & Prevention, vol. 23, no. 1 (1991), pp. 45-52.

outnumbered the courteous: New Jersey Star-Ledger, September 28, 1998.

by low self-esteem: Mayer Perry writes, for example, that “if an individual lacks ‘personal drive’ or dominance, either is easily afforded in the driving situation, and in compensating for this lack, he frequently over-compensates.” Perry, Aggression on the Road (London: Tavistock, 1968), p. 7.

promotes aggressive driving: George E. Schreer, “Narcissism and Aggression: Is Inflated Self-Esteem Related to Aggressive Driving?” North American Journal of Psychology, vol. 4, no. 3 (2002), pp. 333-42.

claim to have had: See Gina Kolata, “The Median, the Math, and the Sex,” New York Times, August 19, 2007.

than doing it: See “Aggravating Circumstances,” a report produced by Public Agenda (available at It could be, of course, that the people in the sample (maybe the kind of people who answer surveys) just happened to be an extraordinarily well-behaved group of drivers who really were subject to an inordinate number of louts (the sort who do not answer surveys). There could also be recall bias at work; it is far easier to remember the isolated aggressive acts of others than the uneventful stream of well-behaved driving. This in itself, however, would not explain why people’s perceptions would have changed over time.

“view of the self”: J. M. Twenge, S. Konrath, J. D. Foster, W. K. Campbell, and B. J. Bushman, Egos Inflating over Time: A Test of Two Generational Theories of Narcissism, 2006. Cited in “Primary Sources,” Atlantic, July-August 2007.

attributes to police officers: Still, getting a ticket may be a form of at least temporarily effective feedback: One study, looking at ten million Ontario drivers for more than a decade, found that each conviction for a traffic offense led to a 35 percent decrease in relative risk of death over the next month for that driver and others. See Donald A. Redelmeier, Robert J. Tibsharani, and Leonard Evans, “Traffic-Law Enforcement and Risk of Death from Motor-Vehicle Crashes: Case-Crossover Study,” Lancet, vol. 361, no. 9376 (2003), pp. 2177-82.

“experience is a mixed blessing”: James Reason, Human Error (Cambridge: Cambridge University Press, 1990), p. 86.

environment for workers: Census of Fatal Occupational Injuries (Bureau of Labor Statistics, 2006). Available at See also P. Lynn and C. R. Lockwood, The Accident Liability of Company Car Drivers, TRL Report 317 (Crowthorne: Transport Research Laboratory, 1998). This study found that company car drivers were 49 percent more likely to be involved in a crash, even after accounting for higher mileage and other factors.

at the bottom: Heinrich’s safety philosophies have proved controversial over the years, but the idea that near misses are scaleable to more serious incidents remains powerful, particularly in traffic, where “human factors,” it is commonly believed, are responsible for up to 90 percent of all crashes. Indeed, a large-scale study of “naturalistic driving behavior” in 2006, which for the first time was able to reliably estimate the near-miss incidents, reported the following distribution after a year’s worth of study: 69 crashes, 761 near crashes, and 8,295 “incidents.” This means, roughly, that for every 120 incidents, there were 11 minor-injury crashes and 1 serious crash—a more robust frequency than that proposed by Heinrich. See, for example, the work of Fred Manuele, such as On the Practice of Safety (New York: Wiley Interscience, 2003).

Investigators learned: Associated Press, May 5, 2007.

killed a motorcyclist: Information on the Janklow case comes from the Argus Leader, August 31, 2003.

“more unintentional than others”: See Teresa L. Kramer, Brenda M. Booth, Han Xiaotong, and Keith D. Williams, “Some Crashes Are More Unintentional Than Others: A Reply to Blanchard, Hicking, and Kuhn,” Journal of Traumatic Stress, vol. 16, no. 5 (October 2003), pp. 529-30.

“hindsight bias”: For a seminal account, see Baruch Fischoff, “Hindsight Is Not Equal to Foresight: The Effect of Outcome Knowledge on Judgment Under Uncertainty,” Journal of Experimental Psychology: Human Perception and Performance, vol. 1, no. 2 (1975), pp. 288-99.

intentional or not: In 1958, this number was said to be 88 out of 100. This figure, taken from a National Safety Council study, comes from H. Laurence Ross, “Traffic Law Violation: A Folk Crime,” Social Problems, vol. 8, no. 3 (1960-61), pp. 231-41.

“then it’s an accident”: Shamus Toumey, “Ryan Crash Kills Man Who Had Just Arrived from Mexico,” Chicago Sun-Times, October 6, 2006.

over the limit and kills someone: In an excellent survey of the legal penalties for drivers who kill “vulnerable road users” (pedestrians and cyclists), Jake Voelcker notes that juries have long been unwilling to levy the most serious charges of manslaughter against even negligent drivers because, as drivers themselves, they expressed a feeling of “there, but for the grace of God, go I.” He cites, as well, examples of subtle bias among judges who imply that accidents are themselves unavoidable—for example, the “accident happened because the appellant was driving rather too fast, as young men will.” The “genuine accident” involving a sober driver, he notes, tends to be avoided by legislation. “Is this simply an unfortunate fact of modern life for which no one is to blame?” he asks. “Or is the driver responsible for the very presence of his car?” Voelcker points to a number of other unresolved legal issues. What should the appropriate penalty be for dangerous driving that narrowly misses killing someone? Why are convicted criminals given harsher sentences for driving-related offenses than others, even when the standard of driving involved in the offense is the same? Should drivers be held to a certain level of causality simply by choosing to operate a machine that is known to be dangerous, thus imposing potential risk on others? See Jake Voelcker, “A Critical Review of the Legal Penalties for Drivers Who Kill Cyclists or Pedestrians,” April 2007. Retrieved from

majority were men: Phillip C. Shin, David Hallett, Mary L. Chipman, Charles Tator, and John T. Granton, “Unsafe Driving in North American Automobile Commercials,” Journal of Public Health, vol. 27, no. 4 (December 2005), pp. 318-25.

themselves as “unlucky”): See Richard Wiseman, The Luck Factor (New York: Miramax Books, 2003).

back in time they happened: See, for example, J. Maycock, C. Lockwood, and J. F. Lester, The Accident Liability of Car Drivers, Research Report No. 315 (Crowthorne: Transport and Road Research Laboratory, 1991).

end of their trip: G. Underwood, P. Chapman, Z. Berger and D. Crundall, “Driving Experience, Attentional Focusing, and the Recall of Recently Inspected Events,” Transportation Research F: Psychology and Behaviour, vol. 6 (2003), pp. 289-304.

more experienced drivers: P. Chapman, D. Crundall, N. Phelps, and G. Underwood, “The Effects of Driving Experience on Visual Search and Subsequent Memory for Hazardous Driving Situations,” in Behavioural Research in Road Safety: Thirteenth Seminar (London: Department for Transport, 2003), pp. 253-66.

experience and expertise: When expert chess players are given a short glimpse of a chess board, for example, they can remember almost twice as much of the board’s positions as novices can. For a discussion of this see Groeger, Understanding Driving, p. 101.

scan the whole picture): See Stine Vogt and Svein Magnussen, “Expertise in Pictorial Perception: Eye-Movement Patterns and Visual Memory in Artists and Laymen,” Perception, vol. 36, no. 1, 2007, pp. 91-100.

“right above the threshold”: For a more detailed account of McGehee’s study, see Daniel V. McGehee, Mireille Raby, Cher Carney, John D. Lee, and Michelle L. Reyes, “Extending Parental Mentoring Using an Event-Triggered Video Intervention in Rural Teen Drivers,” Journal of Safety Research, vol. 38, no. 2 (2007), pp. 215-27.

was not the case: “Vehicle Monitoring Systems Please Providers and Patients,” EMS Insider, August 2004, p. 7.

in the “wrong” lanes: Mohamed Abdel-Aty and J. G. Klodzinski, “Safety Considerations in Designing Electronic Toll Plazas: Case Study,” ITE Journal, March 2001.

when it is minor: E. Walster, “Assignment of Responsibility for an Accident,” Journal of Personality and Social Psychology, vol. 3 (1966), pp. 73-79.

no glass was broken: Elizabeth F. Loftus and John C. Palmer, “Reconstruction of Automobile Destruction: An Example of the Interaction Between Language and Memory,” Journal of Verbal Learning and Verbal Behavior, 1974. This study has been questioned for its “ecological validity” because it took place in a laboratory setting and not in the traumatic, unexpected real-life environment of actually witnessing a car crash and then testifying in court. In those situations, even more distortion could be expected.

“tend to explain”: J. Stannand Baker, “Single Vehicle Accidents on Route 66,” The Journal of Criminal Law, Criminology, and Police Science, vol. 58, no. 4 (December 1967), pp. 58-95.

Chapter Three: How Our Eyes and Minds Betray Us on the Road

“the attention it deserves”: Thanks to Leonard Evans for this quote.

people who study driving: See, for example, Walter Miles, “Sleeping with the Eyes Open,” Scientific American, June 1929, pp. 489-92.

one-third of the time: K. Karrer, S. Briest, T. Vohringer-Kuhnt, T. Baumgarten, and R. Schleicher, “Driving Without Awareness,” Unpublished paper, Center of Human-Machine-Systems, Berlin University of Technology, Germany.

become fully automatic: See John Groeger, Understanding Driving (East Sussex: Psychology Press, 2001), p. 69.

does not seem overly taxing: Studies have suggested that merely changing one’s speed occasionally can help keep a driver more alert. See Pilar Tejero and Mariano Choliz, “Driving on the Motorway: the Effect of Alternating Speed on Drivers’ Activation Level and Mental Effort,” Ergonomics, vol. 45, no. 9 (2002), pp. 605-18.

than on a highway: L. Harms, “Drivers’ Attention Responses to Environmental Variation: A Dual-Task Real Traffic Study,” in Vision in Vehicles, ed. A. G. Gale et al. (Amsterdam: Elsevier Science Publishers, 1986), pp. 131-38.

the less we actually remember: These findings were reported in L. Bergen, T. Grimes, and D. Potter, “How Attention Partitions Itself During Simultaneous Message Presentations,” Human Communication Research, vol. 31, no. 3 (2005), pp. 311-36. See also C. Blain and R. Meeds, “Effects of Television News Crawls on Viewers’ Memory for Audio Information in Newscasts” (unpublished manuscript, Kansas State University, Manhattan, 2004).

10.8 times per hour: See J. C. Stutts, J. R. Feaganes, E. A. Rodgman, C. Hamlett, T. Meadows, D. W. Reinfurt, K. Gish, M. Mercadante, and L. Staplin, Distractions in Everyday Driving (Washington, D.C.: AAA Foundation for Traffic Safety, 2003). Available at:

for 0.6 seconds: L. Tijerina, “Driver Eye Glance Behavior During Car Following on the Road,” Society of Automotive Engineers Paper 1999-01-1300, 1999.

skipping a song: Susan L. Chisholm, Jeff K. Caird, Julie Lockhart, Lisa Fern, and Elise Teteris, “Driving Performance While Engaged in MP-3 Player Interaction: Effects of Practice and Task Difficulty on PRT and Eye Movements,” Proceedings of the Fourth International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design (Iowa City, 2007).

“fifteen-second rule”: See, for example, Paul Green, “The 15-Second Rule for Driver Information Systems,” ITS America Ninth Annual Meeting Conference Proceedings (Washington, D.C.: Intelligent Transportation Society of America, 1999).

“and they’re in trouble”: This raises the interesting question of why people who were following closer than two seconds did not account for the majority of rear-end crashes, as one might suspect. Klauer suggested that when people “are aggressively tailgating, or trying to maintain their position against all vehicles in their surrounding environment, they’re paying very close attention.” Does that mean we should all tailgate? “It’s an interesting finding,” Klauer said. “We tried to be very careful in the way that we reported that, because that’s exactly what we did not want people to take away from this—‘Oh, tailgating is a perfectly safe thing to do.’ All we’re saying is we didn’t see a whole lot of crashes that were a result of it.” This raises the question of which demon you would rather face: the driver hanging far back but talking on a cell phone or the frenetically attentive tailgater.

like changing lanes: A simulator study by William Horrey and Daniel Simons found that drivers under “single” and “dual” task conditions did not change the spacing they allowed during lane changing, unlike the greater headway drivers tend to allow when following a car and talking on a cell phone. The authors suggest that “dual-task interference might be more dangerous when drivers must actively decide how to interact with traffic than when their decisions are constrained by the driving context.” W. J. Horrey and D. J. Simons, “Examining Cognitive Interference and Adaptive Safety Behaviors in Tactical Vehicle Control,” Ergonomics, vol. 50, no. 8 (August 2007), pp. 1340-50.

to their speed: See James Reason, Human Error (Cambridge: Cambridge Univeristy Press, 1990), p. 81.

task got harder: J. Verghese, G. Kuslansky, R. Holtzer, M. Katz, X. Xue, H. Buschke, and M. Pahor, “Walking While Talking: Effect of Task Prioritization in the Elderly,” Archives of Physical Medicine and Rehabilitation, vol. 88, no. 1 (2006), pp. 50-53.

“sample the environment”: A. Oulasvirta, S. Tamminen, V. Roto, and J. Kuorelahti, “Interaction in 4-Second Bursts: The Fragmented Nature of Attentional Resources in Mobile HCI,” Proceedings of CHI 2005 (New York: ACM Press, 2005), pp. 919-28. See also V. Lantz, J. Marila, T. Nyyssönen, and H. Summala, “Mobile Measurements of Mobile Users,” in Lucas Noldus and Fabrizio Grieco, Proceedings of Measuring Behavior 2005: Fifth International Conference on Methods and Techniques in Behavioral Research, ed. (Wageningen, Netherlands, 2005).

longer to do so: J. Hatfield and S. Murphy, “The Effects of Mobile Phone Use on Pedestrian Crossing Behaviour at Signalised and Unsignalised Intersections,” Accident Analysis & Prevention, vol. 39, no. 1 (2006), pp. 197-205.

suffers from a bottleneck: Mei-Ching Lien, Eric Ruthruff, and James C Johnston, “Attentional Limitations in Doing Two Tasks at Once: The Search for Exceptions,” Current Directions in Psychological Science, vol. 15, no. 2 (2006), pp. 89-93.

forgot most of them: For a good summary of this research, see David Shinar, Psychology on the Road: The Human Factor in Traffic Safety (New York: Wiley, 1978), p. 27.

is not useful to our lives: Indeed, scientists have demonstrated, neurologically, how forgetting things helps us in the process of remembering. See Brice A. Kuhl, Nicole M. Dudukovic, Itamar Kahn, and Anthony D. Wagner, “Decreased Demands on Cognitive Control Reveal the Neural Processing Benefits of Forgetting,” Nature Neuroscience, vol. 10 (2007), pp. 908-14.

again for “confirmation”: See Helmut T. Zwahlen and Thomas Schnell, “Driver Eye Scan Behavior When Reading Symbolic Warning Signs,” in Vision in Vehicles VI, ed. A. Gale, I. D. Brown, C. M. Haslegrave, and S. P. Taylor (Amsterdam: Elsevier Science, 1998), p. 3.

(“effectively blind”): See Graham Hole’s concise and authorative study, The Psychology of Driving (Mahwah, New Jersey: Lawrence Erlbaum Associations, 2007), p. 60.

had already been made: H. Shinoda, M. Hayhoe, and A. Shrivastava, “What Controls Attention in Natural Environments?” Vision Research, vol. 41 (2001), pp. 3535-46.

basketball players: Daniel J. Simons and Christopher F. Chabris, “Gorillas in Our Midst: Sustained Inattentional Blindness for Dynamic Events,” Perception, vol. 28 (1999), pp. 1059-74.

locked on the video screen: One of Simon’s key findings is that subjects were less likely to see the gorilla when they were asked to count the number of passes made by the team wearing white T-shirts. This meant, according to Simons, that people did not see the gorilla because it did not look like what they were looking for—or because it did look like what they were ignoring (the team wearing black shirts). As Simons put it, “The more you’re focused on what you expect to see, the less likely you are to see unexpected stuff.”

“failure to see”: The role that a car driver’s vision (or lack thereof) plays in car-motorcycle crashes is huge: For nine of the ten types of leading car-motorcycle crashes, the motorcycle is proceeding in a straight line (with the most common being the car turning left across the path of an approaching motorcycle). See P. A. Hancock, G. Wulf, D. R. Thom, and P. Fassnacht, “Contrasting Driver Behavior During Turns and Straight Driving,” paper presented at the 33rd Annual Meeting of the Human Factors Society, Denver, Colorado, October 1989.

on the road: Another response, of course, is the “loud pipes save lives” approach, by which motorcyclists insist that an ear-shattering exhaust system will surely alert drivers of their presence. The problem is that drivers are often unaware of the direction of such sounds. Another problem is that for the people who have to listen to the loud pipes, the issue of saving motorcyclists’ lives might not exactly be a pressing agenda.

change lanes or slow down: USA Today, July 4, 2007.

moths to a flame: At a meeting I attended in Los Angeles, for example, the California Highway patrol was concerned with a recent spate of these crashes, which had claimed the lives of six officers over just a few months. “For whatever reason they tend to find us on the side of the road,” a CHP officer said at a traffic reporters’ meeting one morning. “It’s just a dangerous place to be.”

we see something interesting: Driving simulator studies have suggested that drivers have a tendency to at least momentarily steer in the direction of their gaze, “in many cases without the conscious awareness of doing so at all.” W. O. Readinger, A. Chatziastros, D. W. Cunningham, H. H. Bülthoff, and J. E. Cutting, “Gaze-Eccentricity Effects on Road Position and Steering,” Journal of Experimental Psychology: Applied, vol. 8, no. 4 (Dec. 2002), pp. 247-58. In an e-mail correspondence, James Cutting made the further point that he thought the reason drivers were not constantly driving off the road when they looked at something had to do with balance: “The ‘looking where you are going’ phenomenon is, I think, strongly related to balance. This is why it is a problem with novice motorcycle drivers, and can have a small effect in walking. Balance is not much an issue in driving (although people do tilt their heads when going into a turn, and they obviously don’t need to). Usually, when driving, one maintains direction while shifting gaze simply because the arm motions to make a turn are not reflexively relative to gaze direction. Balance is.”

their position in the lane: For a concise roundup of moth effect research, see Marc Green, “Is the Moth Effect Real?” Accessed from

while we are moving: See Mark Nawrot, Benita Nordenstrom, and Amy Olson, “Disruption of Eye Movements by Ethanol Intoxication Affects Perception of Depth from Motion Parallax,” Psychological Science, vol. 15, no. 12 (2004), pp. 858-65.

for both cars: Martin Langham, Graham Hole, Jacqueline Edwards, and Colin O’Neil, “An Analysis of ‘Looked but Failed to See’ Accidents Involving Parked Police Vehicles,” Ergonomics, vol. 45, no. 3 (2002), pp. 167-85. Another study found that police cars equipped with the more visible roof-top bar lights were struck just as often as cars with the less visible rear-deck lights, also suggesting that visibility per se may not be the most important factor in these crashes. See Lieutenant James D. Wells Jr., “Patrol-Car Crashes: Rear-End Collision Study—1999,” Florida Highway Patrol, 1999.

typically takes longer: Interestingly, a French study had subjects first take a Stroop test and then participate in a driving test on a closed course that required an unexpected evasive maneuver. Subjects who did poorly on the Stroop test tended to also do less well during the driving exercise. Christian Collet, Claire Petit, Alain Priez, and Andre Dittmar, “Stroop Color-Word Test, Arousal, Electrodermal Activity and Performance in a Critical Driving Situation,” Biological Psychology, vol. 69 (2005), pp. 195-203.

in the way of the less automatic: See Colin M. McLeod, “Half a Century of Research on the Stroop Effect: An Integrative Review,” Psychological Bulletin, vol. 109, no. 2 (1991), pp. 163-201.

(i.e., the word itself): This idea comes from Jennifer J. Freyd, Susan R. Martorello, Jessica S. Alvardo, Amy E. Hayes, and Jill C. Christman, “Cognitive Environments and Dissociative Tendencies: Performance on the Standard Stroop Task for High Versus Low Dissociators,” Applied Cognitive Psychology, vol. 12 (1998), pp. 91-103.

than the arrow: S. B Most and R. S. Astur, “Feature-Based Attentional Set as a Cause of Traffic Accidents,” Visual Cognition, vol. 15 (2007), pp. 125-32.

consultant in California: P. L. Jacobsen, “Safety in Numbers: More Walkers and Bicyclists, Safer Walking and Bicycling,” Injury Prevention, vol. 9 (2003), pp. 205-09. The “safety in numbers” effect has been found in many other studies as well. For example, Noah Radford and David Ragland of the University of California at Berkeley looked at the city of Oakland, California. They found that nearly all of the city’s most dangerous intersections were on the city’s east side, an area with low pedestrian volumes. Only one of the most dangerous intersections for pedestrians was downtown. Noah Radford and David R. Ragland, “Space Syntax: An Innovative Pedestrian Volume Modeling Tool for Pedestrian Safety,” U.C. Berkeley Traffic Safety Center, Paper UCB-TSC-RR-2003-11, December 11, 2003. Available at

the slower they drive: See Kenneth Todd, “Pedestrian Regulations in the United States: A Critical Review,” Transportation Quarterly, vol. 46, no. 4 (October 1992), pp. 541-59.

for a longer period: The Danish transportation planner Jan Gehl makes this point in his seminal book Life Between Buildings (New York: Van Nostrand Reinhold, 1986), p. 79.

safest place to be a cyclist: Conversation with Dan Burden.

asked to remember something: A. M. Glenberg, J. L. Schroeder, and D. A. Robertson, “Averting the Gaze Disengages the Environment and Facilitates Remembering,” Memory & Cognition, vol. 26 (July 1998), pp. 651-58.

thought to aid memory: See A. Parker and N. Dagnall, “Effects of Bilateral Eye movements on Gist Based False Recognition in the DRM Paradigm,” Brain and Cognition, vol. 63, no. 3 (April 2007), pp. 221-25.

other things, like driving: M. A. Recarte and L. M. Nunes, “Effects of Verbal and Spatial-Imagery Tasks on Eye Fixations While Driving,” Journal of Experimental Psychology: Applied, vol. 6, no. 1 (2000), pp. 31-43.

on our mental workload: See, for example, M. C. Lien, E. Ruthruff, and D. Kuhns, “On the Difficulty of Task Switching: Assessing the Role of Task-Set Inhibition,” Psychonomic Bulletin & Review, vol. 13 (2006), pp. 530-35.

for us to process things: C. Spence and L. Read, “Speech Shadowing While Driving: On the Difficulty of Splitting Attention Between Eye and Ear,” Psychological Science, vol. 14 (2003), pp. 251-56.

consumes even more effort: Curiously, this has not been studied extensively per se in driving simulator studies, but the work of Nilli Lavie, at the Institute of Cognitive Neuroscience at University College London, and her colleagues hints at the problem. In a study, subjects were asked to perform a “linguistic task” that was either “high load” or “low load” when the task was low load, they were more likely to notice an irrelevant display of motion than when it was high load. Her finding—that people are unable to ignore irrelevant stimuli when their “perceptual load” is not fully taxed, carries, as she mentioned to me in a conversation, the reverse implication that relevant stimuli will be less likely to be noticed under high-load conditions. See G. Rees, C. D. Frith, and N. Lavie, “Modulating Irrelevant Motion Perception by Varying Attentional Load in an Unrelated Task,” Science, vol. 278 (1997), pp. 1616-19. In more recent research, Lavie found that people engaged in intensive visual tasks were less likely to notice sounds at a low volume. It is not difficult to extrapolate from this that an intensive auditory task—for example, straining to hear a voice at low volume on a cell phone—will exact more pressure on the “perceptual load” and thus reduce performance in performing visual tasks.

they still remembered fewer: David L. Strayer and Frank A. Drews, “Multitasking in the Automobile,” in Attention: From Theory to Practice, ed. A. Kramer, D. Wiegmann, and A. Kirlik (New York: Oxford University Press, 2006).

When first asked this question: This is drawn from a conversation with Benjamin Coifman.

100 miles per hour: Robert Winkler, “The Need for Speed,” New York Times, November 13, 2005.

sequential “frames”: Tim Andrews and Dale Purves, “The Wagon Wheel Illusion in Continuous Light, Trends in Cognitive Neuroscience, vol. 9, no. 6 (2005), pp. 261-63.

demonstration of motion parallax): Mark Nawrot provided me with a simple exercise in “seeing” motion parallax at work: “For example, pick out two objects, near and far, on your desktop. Hold up your two index fingers, near to your face, one below the objects pointing up, one above pointing down. Hold your fingers stationary, fixate on the ‘near’ object, close one eye, and move your head side to side. Easy. Now do the same as you move your top finger along with your head movement so that it ‘matches’ the distant object. If you had to guess, you’d now say your top finger is farther away than your lower finger.” For further interesting research on the mechanics of motion parallax, see Mark Nawrot, “Eye Movements Provide the Extra-retinal Signal Required for the Perception of Depth from Motion Parallax,” Vision Research, vol. 43 (2003), pp. 1553-62.

more realistic: In the scene in The Lord of the Rings in which the “beacons” are being lit to sound the alarm for the impending danger to Rohan, the aerial camera sweeps across the landscape, but the beacon remains in the center of the shot as the background sweeps by. Nawrot suggests that the motion might trigger an involuntary “optokinetic response.” To prevent us from simply being visually swept up in that background movement, however, the eye responds with a “smooth pursuit” movement to effectively countermand the motion and maintain the fixation on the lit beacon. This, Nawrot posits, mimics the series of compensatory eye movements we are constantly making in real life. Mark Nawrot and Chad Stockert, “Motion Parallax in Motion Pictures: The Role of Background Motion and Eye Movements” (unpublished paper, Department of Psychology, North Dakota State University). For a further fascinating discussion on human vision and the movies, see James E. Cutting, “Perceiving Scenes in Film and in the World,” in Moving Image Theory: Ecological considerations, ed. J. D. Anderson and B. F. Anderson (Carbondale: Southern Illinois University Press, 2005), pp. 9-27.

“illusory pavement markings”: Actually, any pavement marking is rather illusory.

reduced their speed: “Evaluation of the Converging Chevron Pavement Marking Pattern,” AAA Foundation for Traffic Safety (Washington, D.C.), July 2003.

have been mixed: “A Review of Two Innovative Pavement Marking Patterns That Have Been Developed to Reduce Traffic Speeds and Crashes,” AAA Foundation for Traffic Safety (Washington, D.C.), August 1995.

at the higher speed: G. G. Denton, “The Influence of Adaptation on Subjective Velocity for an Observer in Simulated Rectilinear Motion,” Ergonomics, vol. 19 (1976), pp. 409-30.

sensation of moving backward: In a study by Stuart Anstis, subjects asked to jog on a treadmill for as little as a minute experienced this aftereffect. Once the treadmill was stopped, subjects asked to jog in place actually jogged, on average, 162 centimeters forward. Anstis notes, “The backward motion of the treadmill produces an artificial mismatch between motor output and normal postural feedback, for which the adaptation compensates or nulls out by adjusting internal gain parameters to bring output and feedback back into line. But once the runner steps on to solid ground these newly adjusted parameters are now inappropriate and manifest themselves as an aftereffect, which dissipates as the parameters automatically update to match the solid ground. So these new aftereffects reveal the continuous neural recalibration of the gait control system.” See Stuart Anstis, “Aftereffects from Jogging,” Experimental Brain Research, vol. 103 (1995), pp. 476-78.

when asked to speed up: For an excellent discussion of this issue see John Groeger, Understanding Driving (East Sussex, Psychology Press: 2001), p. 14.

largely, it is thought: This theory is credited to the pioneering work of J. J. Gibson, who wrote: “The aiming point of any locomotion is the center of the centrifugal flow of the ambient optic array.” Gibson, The Ecological Approach to Visual Perception (Boston: Houghton Mifflin, 1979), p. 182. The “steering” process is much more complicated than this, as we must somehow compensate, like Steadicams, for the fact that our eyes and heads are also moving as we move. For a good discussion of some of these complexities, see William H. Warren, “Perception of Heading Is a Brain in the Neck,” Nature Neuroscience, vol. 1, no. 8 (1998), pp. 647-49. Warren also provides the example of the Millennium Falcon in hyperspace to describe the radial pattern away from the focus of expansion.

“global optical flow”: Not all of our sense of motion comes from visual inputs, of course. The reason I, like many other people, experienced bouts of “simulator sickness” in the various driving simulators in which I drove is that the picture of the moving road I was looking at did not correspond to what my vestibular system (the “balance” system of the inner ear) was experiencing.

our “target”: In an interesting experiment at Brown University, researchers used virtual reality to create an optically impossible situation in which subjects had to walk toward something without the use of optical flow, instead of merely walking toward the object via its egocentric direction (its direction in space relative to the subject). Subjects were less accurate in their approach without the optic flow. See W. H. Warren, Bruce Kay, Wendy Zosh, Andrew Duchon, and Stephanie Sahue, “Optic Flow Is Used to Control Human Walking,” Nature Neuroscience, vol. 4, no. 2 (2001), pp. 213-16.

a kind of radial pattern: This is not an entirely resolved issue and is still being debated. Gibson, for example, observed: “The behavior involved in steering an automobile, for instance, has usually been misunderstood. It is less a matter of aligning the car with the road than it is a matter of keeping the focus of expansion in the direction one must go.” But as vision researcher Michael Land has pointed out, this argument may not account for a driver’s behavior around curves: “On a curved trajectory the locations of the stationary points in the flow-field vary with distance, generating a curved line across the ground plane, not a single focus of expansion.” Land notes that we rely instead of the inner edge of the road in driving around curves, with some 80 percent of driver’s glances being directed in that region. See Michael F. Land, “Does Steering a Car Involve Perception of the Velocity Flow Field?” in Motion Vision-Computational, Neural, and Ecological Constraints, ed. Johannes M. Zanker and Jochen Zeil (New York: Springer Verlag, 2001).

our sense of speed: It has also been argued that optic flow influences our estimates of distance while driving as well. See M. Lappe, A. Grigo, F. Bremmer, H. Frenz, R. J. V. Bertin, and I. Israel, “Perception of Heading and Driving Distance from Optic Flow,” Driving Simulation Conference 2000 (Paris), pp. 25-31.

tree-lined roads: This information comes from T. Triggs, “Speed Estimation,” in Automotive Engineering and Litigations, vol. 2, ed. G. A. Peters and B. Peters (New York: Garland Law Publishing), pp. 569-98.

flow at the same speed: Christopher Wickens, Engineering Psychology and Human Performance (Upper Saddle River, N.J.: Prentice Hall, 2000), p. 162.

those at lower heights: See, for example, Christina M. Rudin-Brown, “The Effect of Driver Eye Height on Speed Choice, Lane-Keeping, and Car-Following Behavior: Results of Two Driving Simulator Studies,” Traffic Injury Prevention, vol. 7, no. 4 (December 2006), pp. 365-72; or B. R. Fajen and R. S. David, “Speed Information and the Visual Control of Braking to Avoid a Collision,” Journal of Vision, vol. 3, no. 9 (2003), pp. 555-555a.

than they intend to: See C. M. Rudin-Brown, “Vehicle Height Affects Drivers’ Speed Perception: Implications for Rollover Risk,” Transportation Research Record No. 1899: Driver and Vehicle Simulation, Human Performance, and Information Systems for Highways; Railroad Safety; and Visualization in Transportation (Washington, D.C.: National Research Council, 2004), pp. 84-89.

speed more than others: See, for example, Allan F. Williams, Sergey Y. Kyrchenko, and Richard A. Retting, “Characteristics of Speeders,” Journal of Safety Research, vol. 37 (2006), pp. 227-32. Of course, any findings that drivers of SUVs and pickups drove faster than other vehicles brings up other “confounding” factors, such as a higher rate of male drivers for those vehicle categories, or the idea that people who choose to drive SUVs and pickups may be more prone to speeding or feel safer and thus are more likely to drive at a higher speed—instead of the vehicle making them more prone to speeding.

slowly than they really were: N Harré, “Discrepancy Between Actual and Estimated Speeds of Drivers in the Presence of Child Pedestrians,” Injury Prevention, vol. 9 (2003), pp. 38-41.

slow down slightly: See “Research Shows Speed Trailers Improve Safety in Temporary Work Zones,” Texas Transportation Researcher, vol. 36, no. 3 (2000).

Some highway agencies: Minnesota Tailgating Pilot Project (St. Paul, Mn: Department of Public Safety, 2006). The Pac-Man information comes from the Star Tribune, December 20, 2006.

how fast they’re going: For a good roundup of research, see Leonard Evans, Traffic Safety (Bloomfield Hills, Mich.: Science Serving Society, 2004), p. 173.

279 feet: I am using the example provided by crash investigator and human factors researcher Marc Green, available at

directly at a fielder: For a fascinating discussion of the complexities of catching a ball, among other things, see Mike Stadler, The Psychology of Baseball (New York: Gotham Books, 2007).

as much as several seconds: Robert Dewar and Paul Olson note that drivers “often perceive a stationary vehicle as moving, even with five seconds’ viewing.” Dewar and Olson, Human Factors in Traffic Safety (Tuscon: Lawyers and Judges Publishing, 2002), p. 23.

no idea of the rate: For a good discussion of this, see Olson and Farber, Forensic Aspects of Driver Perception and Response (Tucson: Lawyers and Judges Publishing Co., 2003), p. 112.

overtaking crashes: The psychologists Rob Gray and David Regan suggest that what is going on here is that as we stare for a while at things like the white stripes on the road, or trees on the side of the road, our brains quickly adapt; they compare the effect to the well-known “waterfall effect”: You stare at water rushing down a waterfall for a while, and then look at a nearby rock—it will seem to be moving upward. When we come off the highway, something similar happens, and it may look to us as if the stop sign at the end of the ramp is farther away than it really is, which is why engineers have tested chevrons and other patterns on off-ramps: to break up the illusion of those white stripes. Rob Gray and David Regan, “Risky Driving Behavior: A Consequence of Motion Adaptation for Visually Guided Motor Action,” Journal of Experimental Psychology: Human Perception and Performance, vol. 26, no. 6 (2000), pp. 1721-32.

really tell the difference: This has long been known to people who study driving. In Human Limitations in Automobile Driving (Garden City: Doubleday, Doran & Company, 1938), authors J. R. Hamilton and Louis L. Thurstone (psychologists at Harvard University) observed: “From eight hundred feet right down to where the other car is almost on top of you, the average eye will not have any idea of the rapidity of motion, or speed, of the oncoming car. It will perceive motion, and that is all. The distance at which motion is first perceived, as we have said above, does not depend very much on the speed of either car. But the distance at which rapidity of motion is perceived depends entirely upon the speed of each car. [italics in original] With two cars traveling 40 miles an hour, that distance where the average eye suddenly perceives rapidity of motion is about 145 feet between cars. When two cars are traveling at 50 miles an hour, that distance is about 70 feet. Now we begin to have some understanding of the reason for the frightful collision accidents on the highway.”

speed of the opposing car: See D. A. Gordon and T. M. Mast, “Driver’s Decisions in Overtaking and Passing,” Highway Research Record, no. 247, Highway Research Board, 1968.

your attempted passing: One study remarked on a “conundrum” about passing difficulty and passing risk, noting that drivers were found “to be somewhat poor at making the judgments required for passing maneuvers, particularly judgments about opposing vehicle speed, but the safety record of passing maneuvers is very good. This suggests that passing maneuvers occur in a relatively forgiving environment. First, while drivers are relatively poor in making passing judgments, many drivers may inherently understand this and make very conservative decisions about passing. Second, the buffer area provided downstream of each passing zone provides a margin of safety against collisions resulting from poor driver judgments.” From “Passing Sight Distance Criteria,” NCHRP Project 15-26, MRI Project 110348, prepared for the National Cooperative Highway Research Program, Transportation Research Board National Research Council, Midwest Research Institute, March 2000.

up by only 30 percent: L. Staplin, “Simulator and Field Measure of Driver Age Differences in Left-Turn Gap Judgments,” Transportation Research Board Record, no. 1485, Transportation Research Board, National Research Council, 1995.

to actually see: R. E. Eberts and A. G. MacMillan, “Misperception of Small Cars,” in Trends in Ergonomics/Human Factors, vol 2, ed. R. E. Ebert and C. G. Eberts (North Holland: Elsevier Science Publishers, 1985).

slower the object seems: H. W. Leibowitz, “Grade Crossing Accidents and Human Factors Engineering,” American Scientist, vol. 73, no. 6 (November-December 1985), pp. 558-62. Leibowitz also noted another potential reason—the “deceptive geometry of collisions”—for overestimating the distance of an approaching train, similar to the problem mentioned with drivers trying to judge the distance of an approaching car. A car and a train that are approaching each other will retain consistent positions. He wrote, “There is no lateral motion, and thus the principal cue to velocity is the increase in size of the visual angle subtended or the expansion pattern…. The rate of increases of the expansion pattern is not linear but rather is described by a hyperbolic function. For distant objects, the rate of change in the expansion is low. As the distance decreases, the visual angle subtended increases at an accelerated rate.” This is somewhat similar to a phenomenon known as “motion camouflage,” which has been observed in the natural world—male hoverflies, for example, move in a way to conceal the fact that they are moving when they are tracking female hoverflies. They do so, it has been argued, by “approaching along a path such that its image projected onto the prey’s eye emulates that of a distant stationary object (a fixed point). During its attack, the predator must ensure that it is always positioned directly between the current position of the prey and this fixed point.” Humans, research has suggested, are also susceptible to this effect. See Andrew James Anderson and Peter William McOwan, “Humans Deceived by Predatory Stealth Strategy Camouflaging Motion,” Proceedings of the Royal Society B: Biological Sciences, vol. 270, Supp. 1 (August 7, 2003), pp. S18-S20.

latter was moving faster: Joseph E. Barton and Theodore E. Cohn, “A 3D Computer Simulation Test of the Leibowitz Hypothesis,” U.C. Berkeley Traffic Safety Center, Paper UCB-TSC-TR-2007-10, April 1, 2007;

human vision is an illusion: See Sandra J. Ackerman, “Optical Illusions: Why Do We See the Way We Do?” HHMI Bulletin, June 2003, p. 37.

(much more at night): Dewar and Olson, Human Factors in Traffic Safety, p. 88.

remember more at night): D. Shinar and A. Drory, “Sign Registration in Daytime and Night Time Driving,” Human Factors, vol. 25 (1983), pp. 117-22.

blind to our blindness: See H. W. Leibowitz, “Nighttime Driving Accidents and Selective Visual Degradation,” Science, vol. 197 (July 29, 1977), pp. 422-23.

as drivers actually do: M. J. Allen, R. D. Hazlett, H. L. Tacker, and B. L. Graham, “Actual Pedestrian Visibility and the Pedestrian’s Estimate of His Own Visibility,” American Journal of Optometry and Archives of the American Academy of Optometry, vol. 47 (1970), pp. 44-49, and David Shinar, “Actual Versus Estimated Night-time Pedestrian Visibility,” Ergonomics, vol. 27, no. 8 (1984), pp. 863-71, and Richard Tyrrel, Joanne Wood, and Trent Carberry, “On-road Measures of Pedestrians’ Estimates of Their Own Nighttime Conspicuity,” Journal of Safety Research, vol. 35, no. 5 (December 2004), pp. 483-90.

drive 20 miles per hour: See Olsen, Forensic Aspects of Driver Perception and Response, p. 157.

through the landscape: The contrast experiment discussed can be viewed at For an interesting discussion of the experiment and the traffic implications, see Stuart Anstis, “Moving in a Fog: Contrast Affects the Perceived Speed and Direction of Motion,” Proceedings of the Conference on Neural Networks, Portland, Ore., 2003.

signs have been set up: See C. Arthur MacCarley, Christopher Ackles, and Tabber Watts, “A Study of the Response of Highway Traffic to Dynamic Fog Warning and Speed Advisory Messages,” TRB 06-3086, Transportation Research Record, National Research Council, Washington, D.C., February 2007.

not brake accordingly: For an excellent discussion of snowplow visibility, see Albert Yonas and Lee Zimmerman, “Improving the Ability of Drivers to Avoid Collisions with Snowplows in Fog and Snow,” Minnesota Department of Transportation, St. Paul, Minn., July 2006.

glances over the shoulder: The rearview mirror information is drawn from Thomas Ayres, Li Li, Doris Trachtman, and Douglas Young, “Passenger-Side Rear-View Mirrors: Driver Behavior and Safety,” International Journal of Industrial Ergonomics, vol. 35 (2005), pp. 157-62.

actually it is half: This example was proposed by the art historian E. H. Gombrich in Art and Illusion (Oxford: Phaidon Press, 1961) and was later confirmed and studied further by Marco Bertamini and Theodore E. Parks in “On What People Know About Images on Mirrors,” Cognition, vol. 98 (2005), pp. 85-104. Their use of the phrase “on mirrors” immediately reveals one of the disconnects we tend to have with mirrors, as we tend to say “in mirrors,” as if the image lurked behind the glass. The authors note, “Both the fact that our image is half the physical size, and the fact that this relationship is independent of how far we are from the mirror, are counterintuitive. However, they become clearer as soon as we realize that a mirror is always located halfway between oneself and our virtual self.”

“they ought to be”: For details on Flannagan’s work with rearview mirrors, see M. J. Flannagan, M. Sivak, J. Schumann, S. Kojima, and E. Traube, “Distance Perception in Driver-Side and Passenger-Side Convex Rearview Mirrors: Objects in Mirror are More Complicated Than They Appear,” Report No. UMTRI-97-32, July 1997.

Chapter Four: Why Ants Don’t Get into Traffic Jams

“cricket war”: William G. Harley, “Mormons, Crickets, and Gulls: A New Look at an Old Story,” Utah Historical Quarterly, vol. 38 (Summer 1970), pp. 224-39.

“black carpet”: From Peter Calamai, “Crickets March with Religious Fervor,” Toronto Star, August 2, 2003.

as a tight swarm: A good way to think about this in human terms, as complex-systems theorist Eric Bonabeau has cleverly done, is to imagine a cocktail party. Each person in the room is given a command: Pick two people at random, A and B, and then place yourself so that A is constantly between B and you. In a room of people, this results in a loose crowd always on the move, shifting to stay in the right position, some people at times drifting around the periphery like timid wallflowers. Now change the rules, however, so that you are always between A and B. Instead of milling, the crowd will clump into a “single, almost stationary cluster.” A seemingly minor change in the way each person acts completely alters the group. Could you have predicted that? From Eric Bonabeau, “Predicting the Unpredictable,” Harvard Business Review, vol. 80, no. 3 (March 2002). For a more in-depth discussion of the dynamics involved, see Bonabeau, Pablo Funes, and Belinda Orme, “Exploratory Design of Swarms,” Proceedings of the Second International Workshop on the Mathematics and Algorithms of Social Insects (Atlanta, GA: Georgia Institute of Technology, 2003), pp. 17-24.

to play by the rules: Matt Steinglass made an important point while writing about a collision that Seymour Papert, the founder of MIT’s Artificial Intelligence Lab, suffered with a motorbike while crossing the street in Hanoi, Vietnam, a city where the traffic behavior is as much explained by “emergent behavior” as it is by formal traffic rules (if not more so): “One thing about emergent phenomena that the pioneers of the field tended not to emphasize is that they are often unkind to their constituent agents: Ant colonies are not very solicitous of the lives of individual ants. Hanoi traffic is a fascinating emergent phenomenon, but it didn’t take good care of Seymour Papert when he became one of its constituent agents.” Steinglass, “Caught in the Swarm,” Boston Globe, December 17, 2006.

the “wrong” direction: For a fascinating discussion of the dynamics of the wave, see I. Farkas, D. Helbing, and T. Vicsek, “Mexican Waves in an Excitable Medium,” Nature, vol. 419 (2002), pp. 131-32. For a simulation and videos, see

none died: Gregory A. Sword, Patrick D. Lorch, and Darryl T. Gwynne, “Migratory Bands Give Crickets Protection,” Nature, vol. 433 (February 17, 2005).

a congested mess: This recalls a number of studies of how animal behavior changes under increasingly crowded conditions. A study that looked at cats found results that sound a lot like rush-hour freeways: “The more crowded the cage is, the less relative hierarchy there is. Eventually a despot emerges, ‘pariahs’ appear, driven to frenzy and all kinds of neurotic behavior by continuous and pitiless attack by all others; the community turns into a spiteful mob. They all seldom relax, they never look at ease, and there is a continuous hissing, growling, and even fighting. Play stops altogether and locomotion and exercises are reduced to a minimum.” Quoted in E. O. Wilson, Sociobiology: The New Synthesis (Cambridge, Mass.: Harvard University Press, 1995), p. 255.

difference in the number of cars: David Shinar and Richard Compton, “Aggressive Driving: An Observational Study of Driver, Vehicle, and Situational Factors,” Accident Analysis & Prevention, vol. 36 (2004), pp. 429-37.

road signs and white stripes: The biologist E. O. Wilson notes that “in general, it appears that the typical ant colony operates with somewhere between 10 and 20 signals, and most of these are chemical in nature.” E. O. Wilson and Bert Holldöbler, The Ants (Cambridge, Mass.: Havard University Press, 1990), p. 227.

army ant trail in Panama: I. D. Couzin and N. R. Franks, “Self-organized Lane Formation and Optimized Traffic Flow in Army Ants,” Proceedings of the Royal Society: Biological Science, v. 270 (1511), January 22, 2003, pp. 139-46.

“pinnacle of traffic organization”: Ant foraging models have been deployed in the human world to improve the routing performance of trucking and other companies. For a good account see Peter Miller, “Swarm Theory,” National Geographic, July 2007.

ongoing labor dispute: Sharon Bernstein and Andrew Blankstein, “2 Deny Hacking Into L.A.’s Traffic Light System,” Los Angeles Times, January 9, 2007.

feel their neighbors’ presence: Stephen Johnson writes that “the problem with all car-centric cities is that the potential for local interaction is so limited by the speed and the distance of the automobile that no higher-level order can emerge…. There has to be feedback between agents, cells that change in response to the changes in other cells. At sixty-five miles an hour, the information transmitted between agents is too limited for such subtle interactions, just as it would be in the ant world if a worker ant suddenly began to hurtle across the desert floor at ten times the speed of her neighbors.” See Johnson, Emergence (New York: Scribner, 2001), p. 96.

even ATSAC’s computers: John Fisher would point this fact out again later in a newspaper story announcing the state of California’s $150 million plan to synchronize all the city’s signals, which, officials announced, could shave commutes by “up to 16%.” Los Angeles Times, October 17, 2007.

more people die in cars each year: Gerald Wilde pointed this out to me.

“pedestrian interference”: See, for example, N. M. Rouphail and B. S. Eads, “Pedestrian Impedance of Turning-Movement Saturation Flow Rates: Comparison of Simulation, Analytical, and Field Observations,” Transportation Research Record, No. 76, Annual Meeting of the Transportation Research Board, Washington, D.C., 1997, pp. 56-63.

to help move the fewer cars: The city of Amsterdam, for example, has instituted a “green wave” for cyclists, so that cyclists moving at 15 to 18 kilometers per hour get a succession of green lights. (Cars, which tend to move more quickly than that, will find themselves seeing more red.) From “News from Amsterdam,” retrieved from

green wave for walking?: Indeed, as the urbanist William H. Whyte pointed out, the signals on Fifth Avenue seem designed to thwart the pedestrian: “Traffic signals are a particular vexation. They are, for one thing, timed to benefit cars rather than pedestrians. Take Fifth Avenue. You want to make time going north. At the turn of the light to green you start walking briskly. You have about 240 feet to go to reach the next light. You will reach it just as the light turns red. Only by going at flank speed, say 310 feet per minute, will you beat the light.” From William H. Whyte, City (New York: Doubleday, 1988), p. 61.

even higher authorities: This is not such a far-fetched premise. A study by a team of researchers at Bar-Ilan University in Israel examined pedestrian behavior in two cities: the “ultra-Orthodox” Bnei Brak and the “secular” Ramat-Gan. While traffic and infrastructure conditions were essentially the same in both locations, pedestrians in Bnei Brak were three times more likely to commit what the researchers judged “unsafe” pedestrian behaviors. This may be a function of the fact that fewer residents of Bnei Brak own cars; thus they’re less cognizant of drivers’ abilities or less willing to consider them. But the researchers suggested another reason, citing studies that note “a strong connection between the belief in supremacy of other laws (i.e. religious laws) over state laws, and a readiness to violate the law.” See Tova Rosenbloom, Dan Nemrodova, and Hadar Barkana, “For Heaven’s Sake Follow the Rules: Pedestrians’ Behavior in an Ultra-Orthodox and a Non-Orthodox City,” Transportation Research Part F: Traffic Psychology and Behaviour, vol. 7, no. 6 (November 2004), pp. 395-404. For more on the link between religious belief and compliance with laws, see A. Ratner, D. Yagil, and A. Pedahzur, “Not Bound by the Law: Legal Disobedience in Israeli Society,” Behavioral Sciences and the Law, vol. 19 (2001), pp. 265-83.

“crosswalk on the Sabbath”: Letter from the Rabbinical Council of California to John Fisher, August 9, 2004.

stops by 31 percent: F. Banerjee, “Preliminary Evaluation Study of Adaptive Traffic Control System (ATCS),” City of Los Angeles Department of Transportation, July 2001.

previous night’s fireworks: In 2005, the CHP reported, there were thirty-four Code 1125-A incidents on Tuesday, July 5, roughly 50 percent more than the previous or following Tuesday. Data provided by Joe Zizi of the CHP.

“driving on ice, literally”: The link between precipitation intervals and crash risk is well-known driver lore, and studies back it up. See Daniel Eisenberg, “The Mixed Effects of Precipitation on Traffic Crashes,” Accident Analysis & Prevention, vol. 36 (2004), pp. 637-47.

for many decades: G. F. Newell, a researcher at the University of California at Berkeley, observed that “in later years, indeed even to the present time, some researchers try to associate with vehicular traffic all sorts of phantom phenomena analogous to the effects in gases. They don’t exist.” He also argued that traffic is not “like any of the idealized models that the mathematical statisticians theorize about. It is messy and can be analyzed only by crude approximations.” G. F. Newell, “Memoirs on Highway Traffic Flow Theory in the 1950s,” Operations Research, vol. 50, no. 1 (January-February 2002), pp. 173-78.

“puzzles remain unsolved”: See Carlos Daganzo, “A Behavioral Theory of Multi-lane Traffic Flow, Part I: Long Homogeneous Freeway Sections,” Transportation Research Part B: Methodological, vol. 36, no. 2 (February 2002), pp. 131-58.

“heterogeneity of driver behavior”: In his superb book Critical Mass, Philip Ball, noting the increasing inclusion of “psychological” and other such factors in traffic modeling, points out a conundrum: “The more complex the model, the harder it becomes to know what outcomes are in any sense ‘fundamental’ aspects of traffic flow and which follow from the details of the rules.” See Philip Ball, Critical Mass (New York: Farrar, Straus and Giroux, 2004), p. 160.

when they followed passenger cars: The researchers who conducted the study speculated that following drivers may believe that SUVs, like tractor-trailers, take longer to stop than a car, and thus it is safer to follow at a closer distance. Another theory is that “ignorance is bliss”—that is, drivers worry less about what they cannot see than what they can (or they merely focus on the vehicle immediately in front of them, rather than a stream of several vehicles, because it seems easier). See James R. Sayer, Mary Lynn Mefford, and Ritchie W. Huang, “The Effects of Lead-Vehicle Size on Driver-Following Behavior: Is Ignorance Truly Bliss?” Report No. UMTRI-2000-15, University of Michigan, Transportation Research Institute, June 2000.

Los Gatos effect: Carlos F. Daganzo, “A Behavioral Theory of Multi-Lane Traffic Flow,” Part I: Long Homogeneous Freeway Sections.” Transportation Research Part B: Methodological, vol. 36, no 2 (Febryary 2002), pp 131-58.

traveling at 55 miles per hour: In 1985, the Highway Capacity Manual, the bible of highway engineers, put maximum capacity at 2,000 vehicles per lane per hour. That was raised to 2,300 in 1994 and raised again in 1998 to its current figure. Drivers, it seems, are willing to drive at a closer distance to the car ahead of them and to do so at higher speeds in the past. Why are drivers willing to take on more risk? It may be because vehicles have better handling, or because drivers are finding themselves having to cover more distance in a commute, and are thus willing to drive more aggressively to reduce the time. See Federal Highway Administration, 2004 Status of the Nation’s Highways, Bridges and Transit: Conditions and Performance (Washington, D.C.: 2004), U.S. Department of Transportation, pp. 4-16. Similarly, where previous estimates calculated that maximum flow occurred at 45 miles per hour, research by Pravin Varaiya in California, drawn from inductor-loop figures, now puts that figure at 60 miles per hour. See Z. Jia, P. Varaiya, C. Chen, K. Petty, and A. Skabardonis, “Maximum Throughput in L.A. Freeways Occurs at 60 MPH,” University of California, Berkeley, PeMS Development Group, January 16, 2001.

that it is being underused: As with many things in traffic, there is a debate as to the actual efficacy of HOV lanes from a traffic point of view (and not a social perspective). Do they improve the total flow of the highway or, more narrowly, simply give HOV drivers a faster trip? Or do they actually accomplish neither? In one study, by University of California researchers Pravin Varaiya and Jaim-young Kwon, based on loop-detector data taken from freeways in the San Francisco area, the HOV lane, it was argued, not only increased congestion in the other lanes (as one might expect if only a minority of drivers are using the HOV lane), but itself suffered from a 20 percent “capacity penalty.” The reason? As it was a single lane, any driver stuck behind a “snail”—in California, driving 60 miles per hour earns you this characterization—in the HOV lane had to travel the speed of the snail (as the other lanes were even slower, it would not do to try to pass the HOV snail). An additional potential complication that has emerged is that in California, cars bearing a hybrid fuel sticker (85,000 of the most recent version were issued) are legally permitted to drive in HOV lanes. Those drivers may indeed wish to travel around 60 miles per hour, as that will produce higher fuel efficiency (as indicated by the in-car displays). In a later study by fellow University of California researchers Michael J. Cassidy, Carlos F. Daganzo, Kitae Jang, and Koohong Chung (of the California Department of Transportation), the authors reexamined Varaiya and Kwon’s data and came to the conclusion that while overall traffic speeds did drop concurrently with the time the HOV lane was actuated (which, it must be pointed out, is precisely when the roads begin to get crowded; hence the HOV lane), they could not attribute this decline to the HOV lanes themselves, and in some cases, the HOV lanes actually enhanced the flow of traffic through troublesome bottlenecks. See J. Kwon and P. Varaiya, “Effectiveness of High-Occupancy Vehicle (HOV) Lanes in the San Francisco Bay Area,” July 2006, available at, and Michael J. Cassidy, Carlos F. Daganzo, Kitae Jung, and Koohong Chung, “Empirical Reassessment of Traffic Operations: Freeway Bottlenecks and the Case for HOV Lanes,” Research Report UCB-ITS-RR-2006-6, December 2006.

nowhere near critical density: “Possible Explanations of Phase Transitions in Highway Traffic,” C. F. Daganzo, M. J. Cassidy, and R. L. Bertini, Department of Civil and Environmental Engineering and Institute of Transportation Studies, University of California, Berkeley, May 25, 1998.

If done properly: This is not to say that ramp meters always work perfectly, because nothing in traffic is ever so easy. Timing patterns may be skewed (although this is being addressed with real-time, system-wide adaptive ramp meters). Ramp metering done without carefully studying the traffic terrain can lead to “perverse outcomes,” one study suggests, as in the case of metered on-ramp drivers being held hostage by a “downstream” off-ramp they will not even use (congestion caused “not by too many cars getting on the freeway but by too many cars trying to get off”). Too many cars held on the ramp, no matter how desirable for the freeway, can back up into local streets, triggering other jams. Needless to say, for metering to work properly, people actually need to obey the signals. There is a fairness issue as well, as the authors of the Minnesota study pointed out: Ramp metering favors those making longer trips and actually hurts those traveling only a few exits. See Michael Cassidy, “Complications at Off-Ramps,” Access magazine, January 2003, pp. 27-31.

one-third less time: The rice experiment (proposed by Paul Haase) was the winning entry in a contest sponsored by the Washington DOT for the best way to visualize “throughput maximization” Susan Gilmore, “Rice Is Nice When Trying to Visualize Highway Traffic,” Seattle Times, December 29, 2006.

“like cars on the highway”: To wit: “Traffic flow resembles granular flow nowhere more closely than on the highway. Here the individual behavior of the drivers forms a relatively small statistical perturbation on the deterministic part of the collective motion, and hence the cars can be treated as physical particles. Both are many particle systems far from equilibrium, in which the constant competition between driving forces and dissipative interactions leads to self-organized structures: Indeed, there is a strong analogy between the formation of traffic jams on the highway and the formation of particle clusters in a granular gas.” From K. van der Weele, W. Spit, T. Mekkes, and D. van der Meer, “From Granular Flux Model to Traffic Flow Description,” in Traffic and Granular Flow 2003, eds. S. P. Hoogendoorn, S. Luding, P. H. L. Bovy, M. Schreckenberg, and D. E. Wolf (Berlin: Springer, 2005), pp. 569-78. On the other hand, G. F. Newell, a seminal traffic flow researcher, once cautioned that “some researchers try to associate with vehicular traffic all sorts of phantom phenomena analogous to the effects in gases. They don’t exist.” G. F. Newell, “Memoirs on Highway Traffic Flow Theory in the 1950s,” Operations Research, vol. 50, no. 1 (January-February 2002), pp. 173-78.

“through the hopper”: Rice is not a perfect metaphor for traffic either. As Benjamin Coifman points out, “Traffic is mostly a one-dimensional system within the lane, with occasional coupling to adjacent lanes. Traditional granular flow is three-dimensional. And then in traffic you are dealing with smart particles.” (Author interview.)

between the grains: The German physicist and traffic researcher Dirk Helbing has observed a similar phenomenon at work in the “outflow” of people from crowded rooms. “Panicking pedestrians often come so close to each other, that their physical contacts lead to the buildup of pressure and obstructing friction effects.” This can occur even when the exits are fairly wide. Why? “This comes from disturbances due to pedestrians, who expand in the wide area because of their repulsive interactions or try to overtake one another.” His simulations have found that columns placed asymmetrically in front of door openings can help “reduce the pressure at the door.” As with rice, when you organize the flow, slower is faster. See Dirk Helbing, “Traffic and Related Self-Driven Many-Particle Systems,” Reviews of Modern Physics, vol. 73, no. 4 (2001), pp. 1067-1141.

with ramp meters than without: See David Levinson and Lei Zhang, “Ramp Meters on Trial: Evidence from the Twin Cities Metering Holiday,” Department of Civil Engineering, University of Minnesota, May 30, 2002; see also Cambridge Systematics, “Twin Cities Ramp Meter Evaluation,” prepared for Minnesota Department of Transportation, February 1, 2001.

rarely have to stop: Jerry Champa, “Roundabout Intersections: How Slower Can Be Faster,” California Department of Transportation Journal, vol. 2 (May-June 2002), pp. 42-47.

1,320 vehicles per hour: Robert Herman and Keith Gardels, “Vehicular Traffic Flow,” Scientific American, vol. 209, no. 8 (December 1963).

more lost time: According to one study, SUVs reduce traffic flow in another way as well, by blocking the view of following drivers, who tend to leave more headway as their sight distance drops and they are less sure of traffic conditions ahead. This, of course, diverges from the findings of another study, cited above in the note for the phrase “when they followed passenger cars.” The difference in results may be due to the different types of roads on which the two studies were conducted or some other unidentified artifact. Kara M. Kockelman and Raheel A. Shabih, “Effect of Vehicle Type on the Capacity of Signalized Intersections: The Case of Light-Duty Trucks,” Journal of Transportation Engineering, vol. 126, no. 6 (1999), pp. 506-12.

stop on red: See, for example, Matt Helms, “Wait Just Two Seconds Before You Start,” Free Press, June 18, 2007.

Drivers talking on cell phones: University of Utah psychology professor David Strayer found in one driving-simulator experiment that subjects talking on a cell phone tended to drive more slowly and make fewer lane changes to avoid slower moving traffic (which may be read as a surrogate for a delayed ability to react). The total of this activity, Strayer estimates, adds 5 to 10 percent to total commuting times (then again, driving more slowly has safety and environmental benefits). See Joel M. Cooper, Ivana Vladisavljevic, David L. Strayer, and Peter T. Martin, “Drivers’ Lane-Changing Behavior While Conversing on Cell Phone in Variable-Density Simulated Highway Environment,” paper submitted to 87th Transportation Research Board meeting, Washington, D.C., 2008.

about 12 miles per hour: Robert L. Bertini and Monica T. Leal, “Empirical Study of Traffic Features at a Freeway Lane Drop,” Journal of Transportation Engineering, vol. 131, no. 6 (2005), pp. 397-407.

wreak progressive havoc: See Philip Ball, “Slow, Slow, Quick, Quick, Slow,” Nature, April 17, 2000. For the original research, see T. Nagatani, “Traffic Jams Induced by Fluctuation of a Leading Car,” Physical Review E, vol. 61 (2000), pp. 3534-40.

effects of a shock wave: See P. Breton, A. Hegy, B. De Schutter, and H. Hellendoorn, “Shock Wave Elimination/Reduction by Optimal Coordination of Variable Speed Limits,” Proceedings of the IEEE Fifth International Conference on Intelligent Transportation Systems (ITSC ’02), Singapore, pp. 225-30, September 2002.

trip times declined: Highways Agency, M25 Controlled Motorways: Summary Report, November, 2004.

slower can be faster: These systems require careful planning, however, to avoid unintended effects. The speed-limit step-down cannot be too sudden, or that itself could cause a shock wave. The ideal system would be coordinated along the length of the highway, to avoid simply sending one well-coordinated group of drivers smack into another jam farther down the road—and inadvertently helping to extend that jam or cause another one. See, for example, P. Breton et al., “Shock Wave Elimination/Reduction by Optimal Coordination of Variable Speed Limits.”

or the opposite: Boris Kerner notes, “The traffic flow instability is related to a finite reaction time of drivers. This reaction time is responsible for the vehicle over-deceleration effect: if the preceding vehicle begins to decelerate unexpectedly, a driver decelerates stronger than is needed to avoid collisions.” From Boris Kerner, The Physics of Traffic: Empirical Freeway Pattern Features, Engineering Applications, and Theory (Berlin: Springer, 2004), p. 69.

each car behind it will stop: One simulation compared the “oscillations” and “amplifications” found in stop-and-go traffic to those found in queues. “Perturbations” in the queue, or the way people stopped and started, were often observed to grow larger from the front to the back of the queue in simulators using cellular automata. See Bongsoo Son, Tawan Kim, and Yongjae Lee, “A Simulation Model of Congested Traffic in the Waiting Line,” Computational Science and Its Applications: ICCSA 2005, vol. 3481 (2005), pp. 863-69.

the harder it is to predict: An interesting parallel has been drawn between the way nonlinear traffic flows behave and the way supply chains work in the world of business. Supply chains suffer from what has been called the “bullwhip effect”—the farther a supplier is from the consumer, the higher the potential for variability (e.g., oversupply or undersupply). For example, when a person orders a beer in a bar, there is direct communication between the patron and the bartender. The order is placed and then filled. But this immediacy becomes increasingly more difficult moving out along the supply chain. If there is a sudden surge in demand for a type of beer at a bar, the bartender will be instantly aware of this; it will take longer for the brewer of the beer to realize this, and even longer for the grower of the hops (and by the time they react to the changed demand, it may have changed again). In traffic, Carlos Daganzo has pointed out, cars flow through a bottleneck rather smoothly; cars far upstream of the bottleneck, however, experience wide “oscillations” in speed. They are less aware of the actual conditions of supply and demand than those cars moving through the bottleneck. See “The Beer Game and the Bullwhip,” ITS Berkeley Online Magazine, vol. 1, no. 2 (Winter 2005).

by the car following them: Gary A. David and Tait Swenson, “Identification and Simulation of a Common Freeway Accident Mechanism: Collective Responsibility in Freeway Rear-End Collisions,” CTS 06-02. Intelligent Transportation Systems Institute, Center for Transportation Studies, University of Minnesota, April 2006.

car was given ACC: The ACC study results are described in L. C. Davis, “Effect of Adaptive Cruise Control Systems on Traffic Flow,” Physical Review E, vol. 69 (2004).

Chapter Five: Why Women Cause More Congestion Than Men

1.1 hours: Andreas Schafer and David Victor, “The Past and Future of Global Mobility,” Scientific American, October 1997, pp. 58-63.

made more frequent, shorter trips: Vacov Zahavi, “The ‘UMOT’ Project,” August 1979, prepared for the U.S. Department of Transportation and the Ministry of Transport, Federal Republic of Germany, Bonn.

in one hour: Cesare Marchetti, “Anthropological Invariants in Travel Behavior,” Technological Forecasting and Social Change, vol. 47 (1994), pp. 75-88.

thirty minutes each way: M. Wachs, B. D. Taylor, N. Levine, and P. Ong, “The Changing Commute: A Case-study of the Jobs-Housing Relationship over Time,” Urban Studies, vol. 30, no. 10 (1993), pp. 1711-29.

jobs were located: See David Levinson and Ajay Kumar, “The Rational Locator,” Journal of the American Planning Association, vol. 60, no. 3 (1994), pp. 319-43. Similar trends have been observed in the Portland area, as described in Robert L. Bertini, “You Are the Traffic Jam: An Examination of Congestion Measures,” paper submitted to Eighty-fifth Annual Meeting of the Transportation Research Board, January 2006, Washington, D.C.

jacking up the numbers: D. Levinson and Y. Wu, “The Rational Locator Reexamined,” Transportation, vol. 32 (2005), pp. 187-202.

prompts more driving: See Nancy McGuckin, Susan Liss, and Bryant Gross, “Do More Vehicles Make More Miles?” National Household Travel Survey (Washington, D.C.: Federal Highway Administration, 2001).

the worse the traffic congestion: Anthony Downs, “Why Traffic Congestion Is Here to Stay…and Will Get Worse,” Access Magazine, no. 25 (Fall 2004). See also Scott F. Festin, Summary of National and Regional Travel Trends: 1970-1995 (Washington, D.C.: U.S. Department of Transportation, Federal Highway Administration, 1996).

figure is 48 percent: Figures supplied by Alan Pisarski.

roughly 16 percent: Alan Pisarski, Commuting in America III (Washington, D.C.: Transportation Research Board, 2006), p. 2.

over 32 miles: Susan Handy, Andrew DeGarmo, and Kelly Clifton, Understanding the Growth in Non-Work VMT, Research Report SWUTC/02/167222 (Austin, Texas: Southwest Region University Transportation Center, University of Texas, February 2002), p. 6.

whole day to complete: For a good discussion of recent changes in women’s travel behavior, see Rachel Gossen and Charles Purvis, “Activities, Time, and Travel: Changes in Women’s Travel Time Expenditures, 1990-2000,” Research on Women’s Issues in Transportation, Report of a Conference, Vol. 2 (Washington, D.C.: Transportation Research Board, 2004).

are now fam-pools: Nancy McGuckin and Nandu Srinivasan, “The Journey-to-Work in the Context of Daily Travel,” paper presented at the Transportation Research Board meeting, Washington, D.C., 2005.

statistically driving more miles: Survey data in the United States indicates what seems like an intuitive fact: The more members in a household, the more miles it drives. “Travel within households increases by household size and income,” as Nancy McGuckin put it to me in an e-mail correspondence.

precocious car poolers: See, for example, Christina Sidecius, “Car Pool Lane Not for Dummies,” Seattle Times, August 2, 2007.

more often than men do: See Research on Women’s Issues in Transportation: Report of a Conference (Washington, D.C.: Transportation Research Board, National Research Council, 2005), p. 30.

about 15 percent do: Jane Brody, “Turning the Ride to School into a Walk,” New York Times, September 11, 2007.

by some 30 percent: See U.S. Environmental Protection Agency, Travel and Environmental Implications of School Siting, EPA 231-R-03-004, October 2003, and Department of Environment, Transport and the Regions, London, Greater Vancouver Regional District, Morning Peak Trip by Purpose, 1999.

sports in America doubled: Charles Fishman, “The Smorgasbord Generation,” American Demographics, May 1999.

trips are getting longer: Handy, DeGarmo, and Clifton, Understanding the Growth in Non-Work VMT.

typical rush hours: See Highway Statistics 2005 (Washington, D.C.: Office of Highway Policy Information, Federal Highway Administration).

closest to their home: Susan L. Handy and Kelly J. Clifton, “Local Shopping as a Strategy for Reducing Automobile Dependence,” Transportation, vol. 28, no. 4 (2001), pp. 317-46.

did a few decades ago: Handy, DeGarmo, and Clifton, p. 31.

it was .79 miles: Handy, DeGarmo, and Clifton, p. 29.

was completely alien: See the report by the Technical Committee of the Colorado-Wyoming Section of the Institute for Transportation Engineers, “Trip Generation of Coffee Shops with Combination Drive-Through and Sit-Down Facilities” retrieved from

left turn during rush hour: Starbucks also anticipates traffic flow in another way: It likes to locate stores near dry cleaners and video rental shops in order to capture the “dropping off” and “picking up” traffic flows (two chances to sell that double latte). See Taylor Clark, Starbucked (New York: Little, Brown, 2007).

stalled queues of cars: Andrew Downie, “Postcard: Brazil,” Time, September 27, 2007. The author drily notes: “Motorbikes account for 9% of the city’s vehicles but they cause more accidents than all the rest combined, according to city traffic officials. That means moto-medics also come with a dose of irony.”

all other travel methods: Pisarski, Commuting in America III, p. 109.

those without one: “Poverty and Mobility in America,” NPTS Brief (Washington, D.C.: U.S. Department of Transportation, Federal Highway Administration, December 2005).

than public transit: See Brian D. Taylor, “Putting a Price on Mobility: Cars and Contradictions in Planning,” Journal of the American Planning Association, vol. 72, no. 3 (Summer 2006), pp. 279-84.

near the top: Daniel Kahneman, Alan Krueger, Norbert Schwarz, and Arthur Stone, “A Survey Method for Characterizing Daily Life Experience: The Day Reconstruction Method,” Science, vol. 306, no. 5702 (December 2004), pp. 1776-78.

but sixteen minutes: Mokhtarian raises the point that people in such surveys may be confusing the idea of “ideal commute” with what commute they would be willing to make; she also notes that they might be giving what they consider to be a “realistic” ideal and not, say zero minutes. See Patricia L. Mokhtariand and Lothlorien S. Redmond, “The Positive Utility of the Commute: Modeling Ideal Commute Time and Relative Desired Commute Amount,” Berkeley: University of California Transportation Center, Reprint UCTC No. 526.

figuring out alternatives: S. Handy, L. Weston, and Patricia L. Mokhtarian, “Driving by Choice or Necessity?” Transportation Research Part A: Policy and Practice, vol. 39, nos. 2-3 (2005), pp. 183-203.

rational perspective: Alois Stutzer and Bruno S. Frey, “Stress That Doesn’t Pay Off: The Commuting Paradox” (September 2004), IZA Discussion Paper No. 1278, Zurich IEER Working Paper No. 151. Available at SSRN:

grown the most: Robert H. Frank, Falling Behind (Berkeley: Univ. of California Press, 2007), p. 82.

“hedonic adaptation”: See S. Frederick and G. Loewenstein, “Hedonic Adaptation,” in Scientific Perspectives on Enjoyment, Suffering, and Well-Being, ed. D. Kahneman, E. Diener, and N. Schwartz (New York: Russell Sage Foundation, 1999), pp. 303-29.

more prone it is to variability: Nancy McGuckin and Nandu Srinivasan, “The Journey-to-Work in the Context of Daily Travel,” paper presented at the Transportation Research Board meeting, 2005. Washington, D.C.

actual time itself: See, for example, Harry Cohen and Frank Southworth, “On the Measurement and Valulation of Travel Time Variability Due to Incidents on Freeways,” Journal of Transportation and Statistics, vol. 2, no. 2 (Dec. 1999), as well as David Brownstone and Kenneth A. Small, “Valuing Time and Reliability: Assessing the Evidence from Road Pricing Demonstrations,” Transportation Research Part A: Policy and Practice, vol. 39, no. 4 (2005), pp. 279-93.

“hell every day”: Jonathan Clements, “Money and Happiness? Here’s Why You Won’t Laugh,” Wall Street Journal, August 16, 2006.

higher rate than are passenger cars: T. Cohn, “On the Back of the Bus,” Access, vol. 21 (1999), pp. 17-21.

into early retirement: The information on urban bus drivers comes primarily from the work of Gary Evans, a professor of human ecology at Cornell University. See, for example, Gary Evans, “Working on the Hot Seat: Urban Bus Drivers,” Accident Analysis & Prevention, vol. 26 (1994), pp. 181-93; G. Evans, M. Palsane, and S. Carrere, “Type A Behavior and Occupational Stress: A Cross-cultural Study of Blue-Collar Workers,” Journal of Personality and Social Psychology, vol. 52 (1987), pp. 1002-07; and Gary W. Evans and S. Carrere, “Traffic Congestion, Perceived Control, and Psychophysiological Stress Among Urban Bus Drivers,” Journal of Applied Psychology, vol. 76 (1991), pp. 658-63.

how much they’re dating: F. Strack, L. L. Martin, and N. Schwarz, “Priming and Communication: The Social Determinants of Information Use in Judgments of Life-Satisfaction,” European Journal of Social Psychology, vol. 18, 1988, pp. 429-42.

“focusing illusion”: Daniel Kahneman, Alan B. Krueger, David Schkade, Norbert Schwarz, and Arthur A. Stone, “Would You Be Happier If You Were Richer? A Focusing Illusion,” Science, vol. 312, no. 5782 (June 30, 2006), pp. 1908-10.

makes them think it is: We are also quite capable of changing the way we feel about something—or the way we think we feel about something—simply by subtly changing our definitions of what is important. A fascinating example of this was seen when a group of psychologists from various countries decided to interview solo drivers before and after a car-pool lane was built on a highway in the Netherlands. They conducted similar interviews on a “control” highway that was not getting a new car-pool lane. When the car-pool lane was added, saving about twenty minutes for those in it, solo drivers’ attitudes seemed to change. It was not as if they suddenly had a more positive opinion of driving alone and a more negative opinion of carpooling, per se. What did change was how important they felt certain aspects of their commute were. Suddenly, “flexibility” ranked as more important, and saving money or travel time less so. On the highway without a car-pool lane, drivers’ attitudes remained the same. But on the highway where the new car-pool lane appeared, teasing solo drivers with its uncongested pleasures, they suddenly had less of a preference for carpooling than when it had not been there. Rather than change their behavior or be haunted every day by not “doing the right thing,” they were suddenly telling themselves new stories about what was important to them. (Interestingly, they did not change their attitudes toward what was best for the environment, even if their own behavior did not follow suit.) They were justifying their actions to themselves—that is, making themselves feel better. It could be that rounding up the car pool would take longer than the lane would save (even if a car pool would still be better for the environment and traffic congestion). It could also be that many people, as mentioned above, simply cannot carpool. But it also seems that people, when actually shown an alternative that would be better for society at large, are good at finding ways to explain why it would not be good for them. A driver stuck in traffic watching a commuter train speed by does not necessarily think, “I wish I were on that train,” but instead tries to console himself with the reasons he cannot be on that train. And so the roads are filled with people wondering why there are so many other people on the roads, all of them convinced of the reasons they need to be there. See Mark Van Vugt, Paul A. M. Van Lange, Ree Meertens, and Jeffrey Joireman, “How a Structural Solution to a Real-World Social Dilemma Failed: A Field Experiment on the First Carpool Lane in Europe,” Social Psychology Quarterly, vol. 59 (1996), pp. 364-74.

less than 15 percent: Brian Taylor, “Rethinking Traffic Congestion,” Access, Fall 2002, pp. 8-16.

like a bell: There are interesting regional variations on this. In Arizona, for example, it has been observed that parking spaces closest to the store are often empty, as cars gravitate first toward the perimeter of the lot, where trees might provide some shade. As one article put it, “A long walk to the store is far better than driving home in a car that has baked for hours in the desert heat.” From Diane Boudreau, “Urban Ecology: A Shady Situation,” Chain Reaction, vol. 4 (2003), pp. 18-19. For more on the microclimate differences between tree-shaded parking lots and those without, see Klaus I. Scott, James R. Simpson, and E. Gregory McPherson, “Effects of Tree Cover on Parking Lot Microclimate and Vehicle Emissions,” Journal of Arboriculture, vol. 25, no. 3 (May 1999), pp. 129-41.

bell-curve arrangement: This idea was first suggested, as far as I can discern, at the following Web site:

not necessarily being chosen: Velkey’s findings matched those predicated by two engineering professors in a “probabilistic model.” See C. Richard Cassady and John E. Kobza, “A Probabilistic Approach to Evaluate Strategies for Selecting a Parking Space,” Transportation Science, vol. 32, no. 1 (January 1998), pp. 30-42.

to walk somewhere: Travel Behaviour Research Baseline Survey 2004: Sustainable Travel Demonstration Towns (SUSTRANS and Socialdata, 2004). Retrieved from

was at work: The “availability heuristic” is credited to Daniel Kahneman and Amos Tversky. (Heuristic is a sophisticated-sounding word that really just means “mental shortcut.”) When people are asked to imagine how often something happens, they tend to overestimate the probability of things that can be more easily recalled from memory—that is, that are “available”—or that loom more vividly in the imagination.

mixed conclusions on this: See, for example, R. G. Golledge, K. L. Lovelace, D. R. Montello, and C. M. Self, “Sex-Related Differences and Similarities in Geographic and Environmental Spatial Abilities,” Annals of the Association of American Geographers, vol. 89 (1999), pp. 515-34.

as the distance did: A. J. Velkey, C. Laboda, S. Parada, M. L. McNeil, and R. Otts, “Sex Differences in the Estimation of Foot Travel Time,” paper presented at the annual meeting of the Eastern Psychological Association, Boston, March 2002. One factor that might lead women to overestimate distances is that, as previous studies have shown, distance estimations tend to be skewed in unpleasant or stressful surroundings. Women may not feel safe in large parking lots, which may help distort the sensation of how close or far a potential parking space is. See Sigrid Schmitz, “Gender Differences in Acquisition of Environmental Knowledge Related to Wayfinding Behavior, Spatial Anxiety and Self-Estimated Environmental Competencies,” Sex Roles: A Journal of Research, July 1999.

“optimal foraging”: For a good introduction to optimal foraging, see T. Schoener, “A Brief History of Optimal Foraging Ecology,” in Foraging Behavior, ed. A. C. Kamil, J. R. Krebs, and H. R. Pulliam (New York: Plenum Press, 1987), pp. 5-67. See also Jeffrey A. Kurland and Stephen J. Beckerman, “Optimal Foraging and Hominid Evolution: Labor and Reciprocity,” American Anthropologist, vol. 87, no. 1 (March 1985), pp. 73-93.

the effort of looking: This example is given in an interesting paper by Elizabeth Newell, a biologist at Hobart and William Smith Colleges, titled “The Energetics of Bee Foraging.” Retrieved from’s.htm.

is the better option: Esa Ranta, Hannu Rita, and Kai Lindstrom, “Competition Versus Cooperation: Success of Individuals Foraging Alone and in Groups,” American Naturalist, vol. 142, no. 1 (July 1993), pp. 42-58.

spot to a destination: Mark Schlueb, “To Get to Game or Show, Parking May Be Tricky,” Orlando Sentinel, December 1, 2006.

destination is in sight: See Daniel R. Montello, “The Perception and Cognition of Environmental Distance: Direct Sources of Information,” in Spatial Information Theory: A Theoretical Basis for GIS (Berlin: Springer, 1997), pp. 297-311, and Lorin J. Staplin and Edward K. Sadalla, “Distance Cognition in Urban Environments,” Professional Geographer, vol. 33 (1981), pp. 302-10.

is “good enough”: See Herbert Simon, Administrative Behavior, 4th ed. (New York: Free Press, 1997).

of their time parked: Donald Shoup, The High Cost of Free Parking (Chicago: American Planning Association, 2005), p. 6.

subsidized parking spots: Bruce Schaller, “Free Parking, Congested Streets,” March 1, 2007; available at

“as has cycle parking space”: City of Copenhagen, Traffic and Environmental Plan 2004, p. 16.

“that will avoid shortages”: Shoup, The High Cost of Free Parking, p. 303.

metered street spots: Donald C. Shoup, “Cruising for Parking,” Transport Policy, vol. 13 (2006), pp. 479-86.

to thirteen minutes: Shoup, The High Cost of Free Parking, p. 279.

“vehicle per block was enough”: William Whyte, City (New York: Doubleday, 1988), p. 72.

all urban traffic collisions: See Paul C. Box, “Curb Parking Findings Revisited,” Transportation Research Circular 501 (Washington, D.C.: Transportation Research Board, 2000).

8 miles per hour: This estimate, for streets with both parking and trees, comes from Dan Burden, “22 Benefits of Street Trees,” Glatting Jackson/Walkable Communities, Summer 2006.

shiny black sealcoat: See Peter C. Van Metre, Barbara J. Mahler, Mateo Scoggins, and Pixie A. Hamilton, “Parking Lot Sealcoat: A Major Source of Polycyclic Aromatic Hydrocarbons (PAHs) in Urban and Suburban Environments,” Fact Sheet 2005-3147 (Austin: U.S. Geological Survey, January 2006). Not surprisingly, the authors report that PAHs seem to be on the rise: “USGS findings show that concentrations of total PAHs in the majority of lakes and reservoirs in urban and suburban areas across the nation increased significantly from 1970 to 2001. The increases were greatest in lakes with rapidly urbanizing watersheds (urban sprawl); for example, over the last 10 years, the concentrations of PAHs in Lake in the Hills (suburban Chicago, Illinois) increased tenfold as the watershed was rapidly developed.”

three to one: Douglas M. Main, “Parking Spaces Outnumber Drivers 3-to-1, Drive Pollution and Warming,” Purdue University News Service, September 11, 2007.

Chapter Six: Why More Roads Lead to More Traffic

during the shutdown: See Jon D. Haveman and David Hummels, California’s Global Gateway: Trends and Issues (San Francisco: Public Policy Institute of California, 2004), p. 62.

“all right by Friday”: See Richard Clegg, “It’ll Be Alright by Friday: Traffic Response to Capacity Reduction,” Department of Mathematics, University of York.

“based on those changes”: This equilibrium effect seems to happen even in extreme cases, like the 2005 transit strike in New York City. Suddenly, private vehicles, the only way to get into the city, needed to carry at least four passengers to enter during the peak hours of five a.m. to eleven a.m. The world was basically turned upside down. On the first day of the strike, the number of vehicles entering the Central Business District was down 24 percent. People were no doubt confused, unsure of what traffic would be like, or hoping for a quick end to the strike. By the second day, 21 percent fewer vehicles than normal entered. People began testing the waters or could not stay home from work any longer. And on the third day, the number was down to 13 percent fewer vehicles. The strike ended that day, so there is no way to know if traffic would have returned to normal; but clearly, people were adapting, either coming in much earlier (traffic levels at four a.m. tripled) or later than normal, or suddenly becoming believers in car pools. The numbers come from “2005 Transit Strike: Summary Report,” New York City Department of Transportation, February 2006.

“for other lines”: This line was quoted in the PBS documentary New York Underground (American Experience).

like population growth: See Lewis M. Fulton, Robert B. Noland, Daniel J. Meszler, and John V. Thomas, “A Statistical Analysis of Induced Travel Effects in the U.S. Mid-Atlantic Region,” Journal of Transportation and Statistics,vol. 3, no. 1 (2000), pp. 1-14. A study in California found that a 1 percent increase in lane-miles creates an immediate increase in vehicle-miles traveled of 0. 2 percent. See Mark Hansen and Huang Yuanlin, “Road Supply and Traffic in California Urban Areas,” Transportation Research A, vol. 31 (1997), pp. 205-18. Robert B. Noland, a scientist at Imperial College London, has compiled an extensive bibliography of “induced demand” research; it’s available at

on the affected roads: See S. Cairns, S. Atkins, and P. Goodwin, “Disappearing Traffic? The Story So Far,” Municipal Engineer, vol. 151, no. 1 (March 2002), pp. 13-22. There was an interesting example of this phenomenon in New York City. When Christo’s The Gates was on display in New York’s Central Park and the roads that crisscross the park were closed to traffic, the city’s transportation department did find local streets more crowded, for the short time that the art was installed. But commute speeds were not hugely affected, largely, according to the DOT, because of special preparations. It is not difficult to imagine that the DOT could also make preparations for closing the park drive to vehicles permanently. The Gates was a huge draw, of course, so we need to factor in how much of the new traffic volume was from people coming to see the art.

congestion itself as an evil: Asha Weinstein Agrawal, a professor of urban planning at San Jose State University, has shown, using Boston as a case study, that the notion of exactly why congestion is bad is quite fluid, often depending on the needs of a political class. At the turn of the century, safety and personal travel time were often invoked as reasons to cure what the mayor called the “evils of congestion,” but by the 1920s, arguments usually tended to focus on the negative economic consequences of congestion, including a rise in the cost of living. Why? “The growing emphasis on congestion and the cost of living was most likely a political effort to convince the larger population that congestion-generated delay was a problem for them, too, even if they didn’t directly experience it as auto drivers,” she writes. “Once the subway eliminated the congestion-induced delay experienced by people traveling downtown on the streetcars, proponents of expensive and controversial congestion relief projects like the loop highway needed a new argument to convince the general public that they should support these policies, and the cost-of-living argument filled that role.” See Agrawal, “Congestion as a Cultural Construct: The ‘Congestion Evil’ in Boston in the 1890s and 1920s,” Journal of Transport History, vol. 27, no. 2 (September 2006), pp. 97-113.

“less crowded roads elsewhere”: Brian D. Taylor, “Rethinking Traffic Congestion,” Access (October, 2002), pp 8-16.

boosts productivity: Timothy F. Harris and Yannis M. Ioannides, “Productivity and Metropolitan Density,” Dept. of Economics, Tufts University, 2000,

the hassles of congestion: Helena Oliviero, “Looking for Love in All the Close Places,” Atlanta Journal Constitution, October 15, 2002, and Katherine Shaver, “On Congested Roads, Love Runs Out of Gas,” Washington Post, June 3, 2002. These citations come from Ted Balaker, Why Mobility Matters to Personal Life, Policy Brief 62 (Washington, D.C.: Reason Foundation, July 2007).

Brookings Institution: See Anthony Downs, Still Stuck in Traffic: Coping with Peak-Hour Traffic Congestion (Washington, D.C.: Brookings Institution, 2004), p. 27.

close to $12 billion: This, and the $108 billion figure, come from Gabriel Roth, ed., Street Smart: Competition, Entrepreneurship, and the Future of Roads (New Brunswick: Transaction Publishers, 2006), p. 7.

since Juvenal’s Rome: Asha Weinstein Agrawal argues that “the essential challenges of traffic congestion are fundamental to urban life, and therefore unlikely to disappear as long as people choose to base their social and economic institutions around the free and frequent interaction that becomes possible in cities and towns.” From “Congestion as a Cultural Construct.”

Dietrich Braess: Dietrich Braess (translated from the orginal German by A. Nagurney and T. Wakolbinger), “On a Paradox of Traffic Planning,” Transportation Science, vol. 39 (2005), pp. 446-50.

J. G. Wardrop: J. G. Wardrop, “Some Theoretical Aspects of Road Traffic Research,” Proceedings of the Institute of Civil Engineers, Part II (1952) pp. 325-78.

total travel time would drop: My example for traffic equilibrium and the Braess paradox was inspired by an article by Brian Hayes, “Coping with Selfishness,” American Scientist, November 2005.

really makes the head spin: When I asked Anna Nagurney, an expert in networks at the University of Massachusetts at Amherst who helped translate Braess’s paper into English, if Braess’s paradox actually exists in the real world, she said that while he was treating the problem mathematically, there is no reason it could not; she also noted that “Braess even lucked out by picking that [traffic] demand because it lies within a range where the Braess paradox will occur.”

“selfish routing”: Tim Roughgarden, Selfish Routing and the Price of Anarchy (Cambridge, Mass.: MIT Press, 2005).

more than $2,000: Aaron Edlin and Pinar Karaca-Mandic, “The Accident Externality from Driving,” U.C. Berkeley Public Law Research Paper No. 130; available at

2.3 cents per mile: The original estimate comes from Ken Small and Camilla Kazimi, “On the Costs of Air Pollution from Motor Vehicles,” Journal of Transport Economics and Policy, January 1995, pp. 7-32. The updating to 2005 dollars is from Ian Parry, Margaret Walls, and Winston Harrington, “Automobile Externalities and Policies,” Resources for the Future Discussion Paper No. 06-26, January 2007.

$10 billion per year: M. A. Delucchi and S.-L. Hsu, “The External Damage Cost of Noise from Motor Vehicles,” Journal of Transportation and Statistics, vol. 1, no. 3 (October 1998), pp. 1-24.

rates and speeds: William T. Hughes Jr. and C. F. Sirmans, “Traffic Externalities and Single-Family House Prices,” Journal of Regional Science, vol. 32, no. 4 (1992), pp. 487-500.

prices often rise: After Clematis Street in West Palm Beach, Florida, was narrowed and retrofitted with bulb-outs and other traffic-calming measures, property values doubled. See “The Economic Benefits of Walkable Communities,” report published by the Local Government Commission Center for Livable Communities, Sacramento, California.

and coronary problems: There is a huge literature examining the potential links between traffic and health; for example, see A. J. Venn, S. A. Lewis, M. Cooper, et al., “Living Near a Main Road and the Risk of Wheezing Illness in Children,” American Journal of Respiratory and Critical Care Medicine, vol. 164 (2001), pp. 2177-80. The fact that houses tend to be cheaper near heavy traffic introduces epidemiological uncertainty, however, because in general the lives of people near the road are not the same, in socioeconomic terms, as those of people living on estates well back from the road. Is it living near the road that gives a person health problems, or are the problems due to something else about the lives of people who dwell near the road?

tendency of birds to breed: Harvard University’s Richard Forman, the dean of the “road ecology” movement, noted in a typical study that bobolinks and other grassland birds in Massachusetts do not breed when their nest sites are close to high-traffic streets (on streets with three thousand or fewer vehicles a day, they do breed). The suggested culprit is noise. See R. T. T. Forman, B. Reineking, and A. M. Hersperger, “Road Traffic and Nearby Grassland Bird Patterns in a Suburbanizing Landscape,” Environmental Management, vol. 29 (2002), pp. 782-800, and R. T. T. Forman, et al., Road Ecology: Science and Solutions (Washington, D.C.: Island Press, 2003). See also J. A. Jaeger, L. Fahrig, and W. Haber, “Reducing Habitat Fragmentation by Roads: A Comparison of Measures and Scales, in Proceedings of the 2005 International Conference on Ecology and Transportation, eds. C. L. Irwin, P. Garrett, and K. P. McDermott (Raleigh: Center for Transportation and the Environment, North Carolina State University, 2006), pp. 13-17.

less able to afford cars: See Donald Appleyard, M. Sue Gerson, and Mark Lintell, Livable Urban Streets: Managing Auto Traffic in Neighborhoods, a report prepared for the Federal Highway Administration, 1976. Many of Appleyard’s findings were reconfirmed in a study by the New York City group Transportation Alternatives, “Traffic’s Human Toll,” 2006; available at

were taxing the poor: It follows that poorer areas also suffer more exposure to the exhaust of passing traffic. Studies in Leeds, England, for example, found that economically disadvantaged areas had higher levels of nitrogen dioxide. See G. Parkhurst, G. Dudley, G. Lyons, E. Avineri, K. Chatterjee, and D. Holley, “Understanding the Distributional Impacts of Road Pricing,” Department of Transport, United Kingdom, 2006.

by Garrett Hardin: See Garrett Hardin, The Tragedy of the Commons.” Science, December 13, 1968.

oft-invoked “tragedy”: Shi-Ling Hsu, “What Is a Tragedy of the Commons? Overfishing and the Campaign Spending Problem,” February 21, 2005, bepress Legal Series, Working Paper 463;

any traffic engineer: Gary Toth, a planner with the New Jersey Department of Transportation, told me in a conversation in early 2007: “We ran a calculation this week for the twenty congestion-related projects that I have in my division. Those twenty represent about ten percent of the congestion in New Jersey. The construction cost to fix those is $6.7 billion.” Given that about $100 million of the department’s $600 to $700 million budget can be spent on congestion projects, he said that “at the rate the public is providing funding for us,” he could expect those congestion projects to be completed in 670 years.

build new ones: See, for example, Joel Kotkin, “Road Work,” Wall Street Journal, August 28, 2007.

all those fuel taxes: Mark Delucchi of the Institute of Transportation Studies at UC-Davis estimates that current payments in the form of fees and taxes by car users to the federal government fall below the costs the federal government pays for car use by some 20 to 70 cents per gallon of fuel. See Mark A. Delucchi, “Do Motor-Vehicle Users in the US Pay Their Way?” Institute of Transportation Studies, Research Report UCD-ITS-RP-07-17, University of California, Davis, 2007.

in the 1960s: See “The Gasoline Tax: Should It Rise?” Wall Street Journal, August 18-19, 2007.

“90 percent of the time”: Martin Wachs, “Fighting Traffic Congestion with Information Technology,” Issues in Science and Technology, vol. 19 (2002), pp. 43-50.

two Canadian researchers: See K. Mucsi and A. M. Khan, “Effectiveness of Additional Lanes at Signalized Intersections,” Institute of Transportation Engineers Journal, January 2003, pp. 26-30. The authors also note that additions to larger intersections will become congested more quickly than additions to smaller crossroads. They write: “If a one-lane road (per direction) gets saturated at 1,000 vehicles per hour (vph) and annual growth is 3 percent, the additional lane will have an uncongested lifetime of approximately 24 years. If a three-lane road (per direction) gets saturated at 3,000 vph and annual growth again is 3 percent, the uncongested lifetime of the additional lane is only 10 years, even without factoring in the diminishing marginal capacity benefit of the additional lane. The diminishing capacity benefits of additional lanes only speed up the process.”

the fourth just 385: Engineers, for their part, have responded to the problems of large intersections by building highway-style overpasses, which are not just expensive but can look rather freakish rising out of an otherwise flat suburban environment, or with the so-called continuous-flow intersection, a breathtakingly complex creature that removes the left-turn conflict from the main intersection by having drivers turn left before they get to the actual intersection; this is a bit unnerving for some drivers, as the design makes it seem as if they are headed into the oncoming lane. Early studies, however, have shown that these designs actually move more traffic more safely than conventional intersections. At an intersection in Baton Rouge, Louisiana, wait times were reduced from four minutes to one. For a good roundup of CFI intersections, with animations, visit AMBD Engineering’s Web site at

an estimated 12.7 percent: This number is taken from H. Teng and J. P. Masinick, “An Analysis of the Impact of Rubbernecking on Urban Freeway Traffic,” Center for Transportation Studies, University of Virginia, Report No. UVACTS-15-0-62, 2004, p. 47.

“it is a bad bargain”: Thomas Schelling, Micromotives and Macrobehavior (New York: W.W. Norton, 2006), p. 125.

photos of incidents: Melissa Leong, “Best and Worst: Driving GTA’s Highways with Sgt. Cam Woolley,” National Post, July 18, 2007.

“or other vehicles”: Andrea Glaze and James Ellis, “Pilot Study of Distracted Drivers,” Center for Public Policy, Virginia Commonwealth University, January 2003.

would have gone up: As a thought experiment, consider that the salad bar was actually free. What would happen? There would be huge queues of people lined up for the free food. As Tim Harford points out, “We recognize that food, clothes, and houses cannot be free or we would have quickly run out of them. It is because roads are free that we have run out of spare road space.” From Harford, The Undercover Economist (Oxford: Oxford University Press, 2004), p. 88.

more people want to use them?: William Vickrey, “Pricing in Urban and Suburban Transport,” American Economic Review, vol. 53 (1963). Reprinted in Richard Arnott, Kenneth Arrow, Anthony B. Atkinson, and Jacques H. Drèze., eds., Public Economics: William Vickrey (Cambridge: Cambridge University Press, 1994).

the results to friends: The Vickrey story is taken from a working paper by Ron Harstad at the University of Missouri, available at

rationalize its loss: For an interesting discussion of these ideas based on laboratory experiments, see Erica Mina Okada and Stephen J. Hoch, “Spending Time Versus Spending Money,” Journal of Consumer Research, vol. 31 (2004), pp. 313-23.

than on another day: Richard Clegg, “An Empirical Study of Day-to-Day Variability in Driver Travel Behavior,” Department of Mathematics, University of York, Heslington. Retrieved at

dropped by 13 percent: Kitchen, in an e-mail, pointed out that all results are “non-equilibrium.” That is, if the roads were actually tolled, traffic speeds would improve, attracting additional users.

increase speeds by 50 percent: John D. McKinnon, “Bush Plays Traffic Cop in Budget Request,” Wall Street Journal, February 5, 2007.

jump by 5 percent: Philip Bagwell, The Transport Revolution (London: Rout-ledge, 1988), p. 375.

go into buses: As Puget Sound’s Kitchen points out, the revenues generated from economically efficient tolling are greater than the total surplus that is gained through drivers’ saved time, which makes the question of how revenues from pricing get redistributed an important, if often neglected, one.

thus more popular: For more on this “virtuous circle,” see Kenneth A. Small, “Unnoticed Lessons from London: Road Pricing and Public Transit,” Access, vol. 26 (2005), pp. 10-15.

show up so often in networks: An interesting example from the traffic world that recalls Laval’s monorail case is Route 29 in Trenton, New Jersey. A product of the 1960s era in which cities elected to build massive high-speed highways through the middles of downtowns or alongside waterways, Route 29 is a dangerous road, with numerous crashes and some two fatalities over a fifteen-year period, as I was told by Gary Toth, an engineer with the New Jersey Department of Transportation. Part of the reason was that cars were “blitzing” down a road that was marked for 45 miles per hour but designed more like a 65-mile-per-hour freeway (with all the standard “safety” provisions of clear zones and the like). Drivers would then inevitably encounter the back of a queue of cars waiting at a signalized intersection; it was a classic “hurry up and wait” situation. Rather than have a bunch of high-speed cars encounter a single light with a long delay, Toth and his colleagues wondered what would happen if Route 29 was converted from a highway into a more aesthetically appropriate and pleasant “urban boulevard,” with a lower speed limit and several more sets of signalized crossings. Wouldn’t that just cause more congestion? Wouldn’t it foist an unconscionable delay upon drivers? When they ran simulations, they found that the new system added only two minutes to the total trip during peak times. Instead of one large queue at a signal, the wait would be redistributed among a set of lights. Importantly, the new system carries the added benefit of being much safer as well, as it involves less sudden braking at high speed.

“for Easter Sunday”: There are other strange dynamics at work; after running simulations, Laval rejected a plan to double the capacity of the Country Bear Jamboree. “People had the perception it was popular because it had such long lines,” he said. “It was really just because it had limited capacity. It’s a common misperception.”

because it is expensive: See, for example, Daniel Machalaba, “Paying for VIP Treatment in a Traffic Jam,” Wall Street Journal, June 21, 2007.

as the toll goes up: As Moshe Ben-Akiva, director of the Intelligent Transportation Systems program at the Massachusetts Institute of Technology, described it to me, the challenge with dynamic pricing is that the price changes depending on your objective: “You may want to charge people for time they actually save. That will mean if congestion builds up on the toll road, you reduce the price. On the other hand, you may want to maintain a certain level of speed on the toll road. If congestion builds up you may want to increase the toll so as to not have stop-and-go traffic on the toll road. There is some confusion going on right now as to what strategy is best.”

by changing their plans: Ronald Koo and Younbin Yim, “Commuter Response to Traffic Information on an Incident,” September 1, 1998, California Partners for Advanced Transit and Highways (PATH), Working Papers: Paper UCB-ITS PWP-98-26;

have some information: In one experimental study, for example, eighteen subjects had to choose between two roads, one of which was faster only if an equal number of people chose the opposite road. The subjects would receive a higher payoff for successfully choosing the quickest route. As it happens, over the long run most people split evenly onto the two roads. But there were “daily” fluctuations, and, more important, these were still happening after two hundred trials. The reason is that people continually tried to outguess each other with better strategies (it turned out drivers did better when they simply chose the same route each time) or find out if the other road was in fact better. Interestingly, in a second trial, drivers were given information about the travel time of the route they did not take, meaning they did not have to change roads to know what the conditions were. The fact that drivers had this information had only a “small effect” on the fluctuation between the two roads from day to day. See Reinhard Selten, Michael Shreckenberg, Thomas Pitz, Thorsten Chmur, and Sebastian Kube, “Experiments and Simulations on Day-to-Day Route Choice-Behaviour,” April 2003, CESifo Working Paper Series No. 900; available at

flocked to the highway: Virginia Groark, “Dan Ryan Traffic Flow Changes by Minute—Like Chicago Weather,” Chicago Tribune, April 5, 2006.

shown the best routes: See Moshe Ben-Akiva, Andre De Palma, and Isam Kays, “Dynamic Network Models and Driver Information Systems,” Transportation Research A, vol. 25A, no. 5 (1991), pp. 251-66.

in two-way traffic: Sarah Murray, “The Green Way to Keep on Trucking,” Financial Times, March 13, 2007.

no longer rise tomorrow: Tim Harford, The Undercover Economist (Oxford: Oxford University Press, 2005), p. 138.

to the same problem: There is an interesting analogy in all this between traffic and the stock market. In theory, as individual investors are able to more closely track the real-time fluctuation of stock prices via the Internet, having access to more and more bits of information about companies, they should be better able to make informed decisions that more quickly translate into stock prices, and market volatility should go down (see Daniel Gross, “Where Have All the Stock Bubbles Gone?” Slate, January 3, 2006). But Brad Barber and Terrance Odean have suggested several potential problems that may arise as a result of many more people having access to inexpensive, almost-instantaneous stock trading via the Internet, including the availability of “faster feedback” that may prompt investors to focus too much on recent performance. Those trying to profit from short-term “momentum cycles,” they write, may actually increase volatility. (They note that individual stocks have increased in volatility over the past several decades, for reasons that they say are not well understood.) Brad M. Barber and Terrance Odean, “The Internet and the Investor,” The Journal of Economic Perspectives, vol. 15, no. 7 (Winter 2001), pp. 41-54.

“once the prediction is broadcast”: Inrix, for example, predicted, ahead of the big I-5 highway closure in Seattle, that traffic would not be as bad as people were making it out to be (for the “disappearing traffic” reasons already mentioned). And it was not. Not everyone heard Inrix’s prediction, however, or at least they did not have enough faith in it against the wall of dire predictions of traffic mayhem. See Danny Westneat, “Math Whiz Had I-5’s number,” Seattle Times, August 22, 2007.

real-time, the better: See I. Kaysi, “Frameworks and Models for the Provision of Real-Time Driver Information” (Ph.D. thesis, Department of Civil Engineering, Massachusetts Institute of Technology, 1992).

travel times and congestion: See, for example, Daniel Florian, “Simulation-Based Evaluation of Advanced Traveler Information Services (ATIS)” (dissertation, Massachusetts Institute of Technology, 2004). For a useful review of previous studies, see David Levinson, “The Value of Advanced Traveler Information Systems for Route Choice,” Transportation Research Part C, vol. 11 (2003), pp. 75-87.

as more people have it: See Levinson, ibid.

for the savvy taxi driver: Other studies, however, have suggested that as more people have information about traffic conditions, traffic can actually get worse. The reason goes back to the noncooperative nature of the traffic network. If everyone is told at once that route A is better than route B, and people self-interestedly and immediately all move to route A, it will no longer be good. People who study networks call these “concentration” and overreaction problems. This is where imperfect information can be worse than no information at all: If no one is told anything, the outcome will be random—each route might be good or bad. It all depends on how quickly people get the information and the choices they make. Ideally, the roads would then be like, for instance, the rows of customs inspectors’ queues at an airport. Everyone can see how much each window is being used at once. If a new window opens up, people can exit every other queue and fill up the new one so that the new queue is as long as the others. The system is in equilibrium. Does it always work so well for the individual, however? You may have moved to the line a bit too slowly and found yourself farther back than you were in the queue you left. You had the information, but did you make the right decision? See H. S. Mahmassani and R. Jayakrishnan, “System Performance and User Response Under Real-Time Information in a Congested Traffic Corridor,” Transportation Research A, vol. 25, no. 5 (1991), pp. 293-307. See also R. Arnott, A. de Palma, and R. Lindsey, “Does Providing Information to Drivers Reduce Traffic Congestion?” Transportation Research A, vol. 25, no. 5 (1991), 309-18, and A. M. Bell, W. A. Sethares, and J. A. Bucklew, “Coordination Failure as a Source of Congestion,” IEEE Transactions on Signal Processing, vol. 51. no. 3, March 2003.

congestion has been passed: In a simulation by David Levinson, a professor of civil engineering at the University of Minnesota, travelers could save the most time through real-time information when traffic conditions were at 95 percent of the available capacity. This is the moment, he suggested, before queues have begun to form and the options begin to dwindle. From Levinson, “Value,” op cit.

huge majority of the traffic: In the Puget Sound study, interestingly, it was found that 5 percent of the tolled networks generated 50 percent of the hypothetical revenue for the study. Data from an e-mail exchange with Matthew Kitchen.

10 percent of the roads: See S. Lammer, B. Gehlsen, and Dirk Helbing, “Scaling Laws in the Spatial Structure of Urban Road Networks,” Physica A, vol. 363, no. 1 (2006), pp. 89-95.

because they are the fastest: A similar dynamic, interestingly, exists in ant-trail formation. As noted in the book Self-Organization in Biological Systems, ants tend to congregate on the paths that lead to the richest food sources or are the fastest: “The shortest path enables ants to minimize the time spent traveling between nest and food source, takes less time to complete, and therefore allows ants to consume their food more quickly, minimizing the risk that a good source of food will be discovered and monopolized by a larger or more aggressive neighboring colony. Shorter paths also mean lower transportation costs.” Attractive trails are visited by more ants, who lay more pheromones, which attracts even more ants, in a “feedback mechanism.” When a trail branches, ants will choose the branch that has been chosen by more ants. See Scott Camazine, Jean-Louis Denéoubourg, Nigel R. Franks, et al., Self-Organization in Biological Systems (Princeton: Princeton University Press, 2001), particularly Chapter 13.

havoc with local roads: In England, for example, rural towns have seen traffic surge on roads that are essentially one-lane tracks, as SatNav-equipped drivers looking for shortcuts are sent on routes that “look good on paper,” as it were, but are ill-prepared to deal with a large influx of new drivers. See David Mill-ward, “End of the Road for Unreliable SatNavs,” Daily Telegraph, June 11, 2006.

was still the best: I kept having this experience. In Phoenix, I tried repeatedly to find alternate routes when I ran into congestion, and the phone, always pleasant, kept advising, “No alternate routes available.”

traffic in things: As pointed out by transportation researcher G. F. Newell, many people are resistant to treating vehicle transportation like any other good. “Economic theory is seriously flawed as applied to transportation,” he wrote, “because most economists treat transportation like a consumer good that can be sold to the highest bidder, but they don’t ask: ‘What does society want?’” He added, “I don’t know either.” See G. F. Newell, “Memoirs on Highway Traffic Flow Theory in the 1950s,” Operations Research, vol. 50, no. 1 (January-February 2002), pp. 173-78.

Chapter Seven: Why Dangerous Roads Are Safer

New York Times observed darkly: Paul J. K. Friedlanden, “H-Day Is Coming to Sweden,” New York Times, August 20, 1967. See also “Sweden May Shift Road Traffic to the Right to Curb Accidents,” New York Times, November 12, 1961; “All Goes Right as Sweden Shifts Her Traffic Pattern,” New York Times, September 4, 1967; “Swedes Face the Trauma of Shifting to Right Side,” New York Times, April 10, 1966; and “Swedes Adjust, Some Grumpily, to Switching Traffic to the Right,” New York Times, September 5, 1967.

year before the changeover: See R. Näätänen and H. Summala, Road-User Behavior and Traffic Accidents (New York: Elsevier, 1976), pp. 139-40.

half that of conventional intersections: The speed and conflict information for roundabouts comes from Timothy J. Gates and Robert E. Maki, “Converting Old Traffic Circles to Modern Roundabouts: Michigan State University Case Study,” in ITE Annual Meeting Compendium (Washington, D.C.: Institue for Transportation Engines, 2000).

about 90 percent: R. A. Retting, B. N. Persaud, P. E. Garder, and D. Lord, “Crash and Injury Reduction Following Installation of Roundabouts in the United States,” American Journal of Public Health, vol. 91, no. 4 (April 2001), pp. 628-31.

about to hit: See Kenneth Todd, “Traffic Control: An Exercise in Self-Defeat,” Regulation Magazine, vol. 27, no. 3 (Fall 2004).

free of junctions): See “The Impact of Driver Inattention on Crash/Near-Crash Risk: An Analysis Using the 100-Car Naturalistic Driving Study Data,” DOT HS 810-594, U.S. Department of Transportation, April 2006, p. 118.

“allow it on the roads”: Jake Voelcker, in his article “A Critical Review of the Legal Penalties for Drivers Who Kill Cyclists or Pedestrians,” makes the useful point that “Health and Safety regulations would not permit thousands of one-tonne steel and glass machines with exposed moving parts to repeatedly pass feet or inches away from unprotected workers on the shop floor at well over 10 m/s (HSE 1998, Sect. 11). Yet this is the situation in our towns and cities today. Why are drivers allowed to impose this danger on pedestrians without more strict prosecution of liability?” Retrieved from

no posts: V. P. Kallberg, “Reflector Posts—Signs of Danger?” Transportation Research Record, vol. 1403, pp. 57-66.

than when it is not: See, for example, S. Comte, A. Várhelyi, and J. Santos, “The Effects of ATT and Non-ATT Systems and Treatments on Driver Speed Behaviour,” Working Paper R 3.1.1 in the MASTER project, VTT Communities & Infrastructure (VTT, Finland), August 1997.

it confuses traffic people too: See Raymond A. Krammes, Kay Fitzpatrick, Joseph D. Blaschke, and Daniel B. Fambro, Speed: Understanding Design, Operating, and Posted Speed, Report No. 1465-1 (Austin, TX: Texas Dept. of Transportation, March 1996).

“time-consuming effort”: See David Shinar, Psychology on the Road: The Human Factor in Traffic Safety (New York: Wiley, 1978), p. 87.

in the period studied: Neal E. Wood, “Shoulder Rumble Strips: A Method to Alert ‘Drifting’ Drivers,” Pennsylvania Turnpike Commission, Harrisburg, Pennsylvania, January 1994.

nor is it always easy to locate: Think for a moment about when you come across a hill on a freeway. It is rarely very steep, but then again, it is not flat. Notice how the road gently unspools before you as you near the crest of the hill. The road has been designed so that if there is an unexpected obstacle lurking over that hill, the average driver should be able to see it and have enough time to react and stop. This seems like a smart idea. But how high should the imaginary obstacle be? What would make the road “safe”? Ezra Hauer, a retired Canadian professor of engineering, has observed that early on, highway engineers settled on a four-inch obstacle—a hypothetical “dead dog.” They did not know whether three-inch obstacles might also be dangerous, or even how many people were hitting four-inch roadkill as they came over a hill. All they really knew was that building the road so that drivers could stop in time for a three-inch obstacle would require more excavating, and thus more money. Little decisions like this may seem trivial, but in a larger sense they literally help shape the way our world looks to us (and how people behave in it). And so for every highway on a hill in America, the road was designed so the average driver could stop in time for a four-inch “dead dog.” In the absence of real information about how, why, and when obstacles on the road lead to crashes, this was, at the very least, prudent engineering, Hauer argues, based on the most efficient construction costs. But over time, something strange happened. Cars began to get lower. Suddenly, drivers could not see the four-inch obstacle in the given time. So the “dead dog” grew two inches taller—even though, Hauer says, “no link has been found between the risk of collisions with small fixed objects on crest curves and the available sight distance.” New roads were built with the new standard (and on existing roads, the driver had just better pray there were no four-inch dogs lying around). Things have since gotten even more complicated. The popularity of SUVs and pickup trucks in the United States means there is “some evidence,” as Ray Krammes told me, that cars are now getting higher. Is it time to lower the dead dog? See Ezra Hauer, “Safety in Geometric Design Standards,” Toronto, Ontario, 1999. Retrieved from

in the United States alone): Steve Moler, “Stop. You’re Going the Wrong Way!” Public Roads, vol. 66, no. 2 (September-October 2002).

moving smoothly triples: The literature on weaving sections is surprisingly enormous, but for a good summary of weaving-section research and dynamics, see Richard Glad, John C. Milton, and David K. Olson, Weave Analysis and Performance: The Washington State Case Study (Olympia, Wash.: 2001).

safer and more efficient: See, for example, Richard W. Glad, Milton, and Olson, ibid.

be less safe: This information comes from an unpublished paper by Ezra Hauer, “Lane Width and Safety” (review of literature for the Interactive Highway Safety Design Model, 2000); accessed at

not statistically significant. See Karin M. Bauer, Douglas W. Harwood, Karen R. Richard, and Warren E. Hughes, “Safety Effects of Using Narrow Lanes and Shoulder-Use Lanes to Increase the Capacity of Urban Freeways,” Transportation Research Record: Journal of the Transportation Research Board, vol. 1897 (2004). On a side note concerning the phrase “statistically significant,” Ezra Hauer cautions that statisticians and policy makers often take the phrase “statistically not significant,” when referring to a traffic-safety study, to mean there would be no cost or benefit to implementing or not implementing some policy or another. Hauer points as one example to a series of studies examining the adoption of “right turn on red” laws; all showed higher crash rates after right turn on red was adopted. None were “statistically significant,” but all “pointed in the same direction”: Allowing right turns on red led to more crashes. See Hauer, “The Harm Done by Tests of Significance,” Accident Analysis & Prevention, vol. 36 (2004), pp. 495-500.

“to the road they see”: See Hauer, “Lane Width and Safety,” op cit.

already on the road: See Robert E. Dewar and Paul L. Olson, Human Factors in Traffic Safety (Tucson: Lawyers and Judges Publishing, 2002), p. 429. David Shinar writes of the “double jeopardy” of misidentified signing. “Misidentified signs compromise safety by taking more time from the driving task and leading drivers to make incorrect decisions. But signs that are interpreted as opposite of their intended meaning mislead the drivers who seem to respond to them as quickly as they do to signs that they identify correctly. Indicating that in these infrequent cases the drivers are sure, but wrong.” See Shinar, Traffic Safety and Human Behavior (Amsterdam: Elsevier, 2007), p. 168.

not put them up: See Supplemental Advance Warning Devices: A Synthesis of Highway Practice, National Cooperative Highway Research Program Synthesis 186 (Washington, D.C.: National Academy Press, 1993), p. 38.

fewer deer had crossed: See T. M. Pojar, D. F. Reed, and T. C. Reseigh, “Effectiveness of a Lighted, Animated Deer Crossing Sign,” Journal of Wildlife Management, vol. 39, no. 1 (1975), pp. 87-91.

“deer-vehicle collision”: See K. M. Gordon, S. H. Anderson, B. Gribble, and M. Johnson, “Evaluation of the FLASH (Flashing Light Animal Sensing Host) System in Nugget Canyon, Wyoming,” Report No. FHWA-WY-01/03F, University of Wyoming, Wyoming Cooperative Fish and Wildlife Research Unit (Laramie, Wy.: July 2001).

MOOSE SIGNS AHEAD: The moose story comes from Robert Finch, “Moose Signs Ahead,” Orion, July-August 2007, p. 7.

“they’ll behave like that”: Monderman’s suspicion of traffic signs was not necessarily a radical stance. The Manual on Uniform Traffic Control Devices, the bible of American traffic engineers, itself has a warning about warning signs: “The use of warning signs,” it notes, “should be kept to a minimum as the unnecessary use of warning signs tends to breed disrespect for all signs.”

is cognitive dissonance: Whether a driver actually gets the ticket may depend on several factors, as a study by Thomas Stratmann and Michael Makowsky argued. “The farther the residence of a driver from the municipality where the ticket could be contested,” they wrote, “the higher is the likelihood of a speeding fine, and the larger the amount of the fine. The probability of a fine issued by a local officer is higher in towns when constraints on increasing property taxes are binding, the property tax base is lower, and the town is more dependent on revenues from tourism.” From Michael Makowsky and Thomas Stratmann, “Political Economy at Any Speed: What Determines Traffic Citations?,” January 31, 2007; available at

dawn of the car itself: According to the research of one historian, the speed bump was first introduced in Chatham, New Jersey, on April 22, 1906. As reports noted, the paved stone in the road was meant to combat “automobile scorchers,” as speeders were then known. See Peter Applebome, “Making a Molehill Out of a Bump,” New York Times, April 19, 2006.

are to violate them: Drivers, it turns out, already tend to treat stop signs like “Slow” signs. A study by Michael DeCesare that looked at a sample of 2,390 vehicles at several intersections in the northeastern United States found that only 14 percent of the group came to a complete stop. Most drivers simply “paused,” and those that did come to a complete stop often did so only because there were already other cars crossing through the intersection. Interestingly, no cars completely violated the stop signs, which implies that stop-sign visibility was not an issue. See “Behavior at Stop Sign Intersections: A Matter of Convenience and Threat of Danger,” paper presented at the Annual Meeting of the Eastern Sociological Society, Boston, 1999.

to make up time: See, for example, Gerald L. Ullman, “Neighborhood Speed Control—U.S. Practices,” ITE Compendium of Technical Papers (1996), pp. 111-15, and Richard F. Beaubein, “Controlling Speeds on Residential Streets,” ITE Journal, April 1989, pp. 37-39.

time to speed: Reid Ewing, “U.S. Experience with Traffic Calming,” Institute of Transportation Engineers Journal, August 1997, p. 30.

to these trips: Crysttal Atkins and Michael Coleman, “Influence of Traffic Calming on Emergency Response Times,” Institute of Transportation Engineers Journal, August 1997.

“fatigue of getting upstairs”: Charles Dickens, “Street Accidents,” All the Year Round, vol. 8 (1892; repr.), p. 499.

often without supervision: For a good history of the woonerven, see Michael Southworth and Eran Ben-Joseph, Streets and the Shaping of Towns and Cities (New York: McGraw-Hill, 1996).

acting accordingly in the moment: Interestingly, this idea has had precedents here and there in the history of traffic engineering. In July 1927, the American magazine Nation’s Traffic reported on a novel signal system at a four-way intersection that featured white lights instead of the traditional amber. When the lights in all four directions shone white, it signified that cars in all four directions could make left turns. Instead of mayhem during the evening rush hour, the writer reported, “We saw four streams of traffic making left turns at the same time…without the scraping of a fender.” The local police chief made an interesting observation: “We have taught these people to sort of care for themselves.” From Gordon Sessions, Traffic Devices: Historical Aspects Thereof (Washington, Institute of Traffic Engineers, 1971), p. 50.

the less we see: This is particularly true at roundabouts. An observational study in Finland found that drivers entering a roundabout were less likely to look to the right and more likely to violate the right-of-way of cyclists crossing to the right. See Heikki Summala and Mikko Rasanen, “Top-Down and Bottom-Up Processes in Driver Behavior at Roundabouts and Crossroads,” Transportation Human Factors, vol. 2, no. 1 (2000), pp. 29-37.

around 20 miles per hour: When I presented this theory to Daniel Lieberman, a professor of biological anthropology at Harvard University’s Skeletal Biology Lab, he answered, via e-mail: “I would agree with you that natural selection would have to have permitted the skeleton to survive falls from running and other such natural events, but we were never designed to be hit by 1-ton cars going at 60 MPH (a lot of momentum). But is running the highest natural force a body experiences? Not sure. We also got hit on the head, attacked by saber-tooths, etc. But it is clearly the case that running is a common way to injure ourselves since we are naturally awkward unstable creatures more likely to fall than quadrupeds, and more likely to get injured by a fall (farther to go). So you might indeed be right.”

running a red light: In 2000, for example, more than one thousand people were killed in crashes caused by someone running a red light, according to the Federal Highway Administration. Figure retrieved from

people on foot: This raises the question of what happens at intersections without “Walk”/“Don’t Walk” signals. Picture the mayhem as ill-behaved pedestrians cross willy-nilly without being told when to do so. At the time of this writing, it was possible to see this in New York City (although plans were afoot to install pedestrian signals). Simply go to Park Avenue, anywhere from Forty-sixth Street to Fifty-sixth Street. There you will notice that not only are the traffic lights smaller but there are no pedestrian crossing signals (called “ped heads”). For unique structural reasons owing to a commuter train running underneath the street, traffic authorities for years were unable to install the necessary foundation for a standard signal. So are pedestrians hit by cars more frequently at these corners? A five-year “crash map” put together by the city DOT showed that there were no more pedestrians struck in that section of Park Avenue than in the areas immediately to the north and south that had ped heads. This suggests that pedestrians on those blocks were forced to more actively assess the danger posed by cars. The crash map was put together by the New York City Department of Transportation’s Pedestrian Projects office and was supplied to me by Michael King. To fully assess the actual risk faced by pedestrians at those sections of Park Avenue versus other areas, and the reasons why, a comprehensive study would have to be undertaken to determine pedestrian volumes and analyze the causative factors of the crashes. If more pedestrians are struck at those corners, the reason might also have to do with the below-standard traffic signals for vehicles. As Michael Primeggia, the deputy commissioner at the city’s Department of Transportation, noted to me in a conversation, vehicle crashes are higher at those corners; particularly “right-angle collisions,” which are often attributed to a car’s failure to stop at a red.

their own green light: This is why engineers often install the “leading pedestrian interval,” or LPI, which gives an “exclusive phase” of a few seconds or so to the walker, to give him a head start and allow him to assert his authority in the crosswalk. This, of course, slows vehicular traffic flow. The most radical example of a pedestrian-only phase is the so-called Barnes dance, named after New York City’s longtime traffic commissioner, in which pedestrians are given the “Walk” signal in both directions and cars in all directions must wait. The Barnes dance was not actually invented in New York City, as is often thought, but in Barnes’s previous posting of Denver. After he unveiled an all-way pedestrian phase, a local scribe wrote, “Barnes has made the people so happy they’re dancing in the streets” hence the Barnes dance. See Henry Barnes, The Man with Red and Green Eyes (New York: Dutton, 1965), p. 116.

for the health of pedestrians: D. F. Preusser, W. A. Leaf, K. B. Debartla, and R. D. Blomberg, The Effects of Right-Turn-on-Red on Pedestrians and Bicycle Accidents, NHTSA-DOT/HS-806/182 (Dunlap and Associates, Darien, Conn.: October 1981).

law than while not: In a study that looked at a year’s worth of pedestrian and bicycle fatalities (1997), drivers were found to be “at least partly culpable” in 71 percent of the cases. See Charles Komanoff, “Killed by Automobile: Death in the Streets in New York City, 1994-1997,” March 1999. In 2004, nearly one-third of all pedestrians killed in New York City were killed in the crosswalk of an intersection. Of all the pedestrian fatalities, the majority (114, or 67.5 percent) were not attributed to any action by the pedestrian, while the categories that reasonably indicate pedestrian blame (“darting, running, or stumbling into road,” “improper crossing of roadway or intersection,” “failure to obey traffic control devices, traffic officers, traffic laws, etc.,” and “walking, playing, working in roadway”) total 48 of 169 fatalities, or roughly 28 percent. See Claire E. McKnight, Kyriacos Mouskos, Camille Kamga, et al., NYMTC Pedestrian Safety Study, Institute for Transportation Systems, City University of New York; prepared for the New York Metropolitan Transportation Council, February 27, 2007.

must navigate several lanes: The undisputed king of marked crosswalk studies is Charles Zegeer, at the University of North Carolina. See Charles V. Zegeer, J. Stewart, and H. Huang, Safety Effects of Marked Versus Unmarked Crosswalks at Uncontrolled Locations: Executive Summary and Recommended Guidelines, 1996-2001 (Washington, D.C.: Federal Highway Administraion, March 2002); available at

make things safer: See David R. Ragland and Meghan Fehlig Mitman, “Driver/Pedestrian Understanding and Behavior at Marked and Unmarked Crosswalks,” U.C. Berkeley Traffic Safety Center, Paper UCB-TSC-RR-2007-4, July 1, 2007; See also Meghan Fehlig Mitman and David R. Ragland, “What They Don’t Know Can Kill Them,” U.C. Berkeley Traffic Safety Center, Paper UCB-TSC-TR-2007-2, April 1, 2007;

a good thing for pedestrians: Conversely, knowing traffic laws such as right-of-way can be dangerous. A study in Finland that looked at collisions between cars and bicycles found that while only 11 percent of cars reported seeing the bicyclist before the crash, some 68 percent of cyclists reported seeing the car—and 92 percent of those who noticed the car assumed it would yield the right-of-way. See Summala and Rasanen, “Top-Down and Bottom-Up Processes,” op. cit.

of their own safety: One reason for this is the “multiple-threat collision,” in which one driver stops but a driver in the next lane does not, most likely because his view of that pedestrian is blocked. This was described to me in a conversation with Charlie Zegeer at the University of North Carolina, a traffic-safety researcher who has spent more time than anyone studying the problems of getting pedestrians across the road safely. See also Zegeer, Stewart, and Huang, Safety Effects, op. cit.

in the face of oncoming traffic: M. Winnet, S. Farmer, J. Anderson, and R. Lockwood, “An Evaluation of the Effect of Removing White Centre Lines,” report prepared for the Wiltshire County Council by CEEMA Ltd. and TRL Limited.

to drive faster: This is an old saw in traffic engineering. In the 1922 book Good Roads, for example, author James McConaghie notes that “it has been found that by placing a series of lines on the pavement, dividing the space up into its maximum number of traffic lanes, a greater speeding up of traffic has been the result.” Quoted in Sessions, Traffic Devices, p. 104.

insufficiently wide bike lanes: See D. L. Harkey and J. R. Stewart, “Evaluation of Shared-Use Facilities for Bicycles and Motor Vehicles,” Transportation Research Record 1578, Transportation Research Board, Washington, D.C., 1997. For a less scientifically rigorous but no less interesting report, see Pete Ownes, “The Effect of Cycle Lanes on Cyclists’ Road Space,” Warrington Cycle Campaign, October 2005. Other studies have made the point that bicycle lanes reduce the amount of vehicle “displacement”—that is, how much they veer toward the center line or even into the other lane—and that bicycles themselves stay on a straighter path in the presence of lanes. See Bonnie J. Kroll and Melvin R. Ramey, “Effects of Bike Lanes on Driver and Bicyclist Behavior,” Journal of Transportation Engineering, vol. 103, no. 2 (March-April 1977), pp. 243-56, and S. R. McHenry and M. J. Wallace, Evaluation of Wide Curb Lanes as Shared Lane Bicycle Facilities, Report FHWA/MD-85/06, Maryland Department of Transportation, Baltimore, August 1985.

system was more dangerous!: The Laweiplein information comes from an unpublished study by Jeroen van Doome and Jelmer Herder of the Leeuwarden Technical College. The data is still preliminary and, as in all such studies, it can be difficult to immediately attribute reasons for increases or decreases in crashes. There may still be lingering “novelty effects” in the scheme, as well as a possibility of a “regression to the mean,” whereby statistical entities such as crash statistics possess a natural tendency to fluctuate. More time will be needed to fully assess the scheme. The reader might well wonder whether the safety and traffic improvements made in Drachten could have been achieved by simply converting the space to a conventional roundabout. But the Leeuwarden report notes that the traffic improvements at Drachten outperform what would be expected using modeling for a “conventional roundabout.” Hamilton-Baillie pointed out to me in an e-mail that the geometry of the scheme differs from that of a conventional roundabout: “By narrowing the entrances and exits—they are 6 meters wide—there’s very little flaring. It doesn’t seem to be a problem for traffic to just allow pedestrians and bicycles to just filter through.” The Laweiplein design, he maintains, avoids some of the problems of how to accommodate pedestrians and bicycles, a common criticism of roundabout schemes. On the idea that users thought the system was more dangerous, when it was statistically not, there is evidence that this kind of distortion is not uncommon. In a study conducted on the University of North Carolina at Chapel Hill campus, a group of students were surveyed as to what they thought the most dangerous areas on campus were for pedestrians. Some locations that people thought were “safe” had actually had a number of crashes, even more so than areas they labeled “dangerous.” See R. J. Schneider, R. M. Ryznar, and A. J. Khattak, “An Accident Waiting to Happen: A Spatial Approach to Proactive Pedestrian Planning,” Accident Analysis & Prevention, vol. 36, no. 2 (March 2004), pp. 193-211.

made on bicycles: From “Cycling for Everyone: The Key to Political and Public Support,” by John Pucher, Rutgers University. Document retrieved from April 8, 2007.

for minor injuries: The Kensington High Street statistics are found in Graeme Swinburne, “Report on Road Safety in Kensington High Street,” Royal Borough of Kensington and Chelsea, London.

“for no inconsiderable time”: Charles Dickens, Sketches by Boz (1835; repr. London: Penguin Classics, 1996), p. 92.

“you need freeways”: Walter Kulash, of Glatting Jackson, described to me a similar tension in terms of traffic flow. “One thing we have learned,” he said, “is that streets are always a bundle of competing interests. There is always going to be less of one thing if there is more of another thing. If there is more seclusion and streets are by their very layout incapable of carrying any through traffic…then a negative is going to pop up somewhere else. And that negative is unbearable arterial streets.”

twelfth-deadliest road in America: Scott Powers, “Colonial One of Nation’s Most Dangerous Roads,” Orlando Sentinel, November 21, 2004. The U.S. 19 information is taken from a survey conducted by NBC’s Dateline; see Josh Mankiewicz, “Dangerous Roads,” Dateline, June 7, 2005.

would have deemed safer: For the details of Eric Dumbaugh’s studies I have drawn on several sources. The first is his unpublished Ph.D. dissertation: “Safe Streets, Livable Streets: A Positive Approach to Urban Roadside Design” (Georgia Institute of Technology, August 2005). I also used a related article: Eric Dumbaugh, “Safe Streets, Livable Streets,” Journal of the American Planning Association, vol. 71, no. 3 (Summer 2005), pp. 283-300.

26 to 30 miles per hour: National Highway Traffic Safety Administration, “Literature Review on Vehicle Travel Speeds and Pedestrian Injuries,” DOT HS 809 021, October 1999.

by some 10 percent: See, for example, M. Martens, S. Comte, and N. Kaptein, “The Effects of Road Design on Speed Behavior: A Literature Review,” Technical Research Centre of Finland VTT, Espoo, 1997. Moreover, a survey of street segments in Connecticut, Massachusetts, and Vermont revealed that on-street parking itself seems to have a safety benefit. The researchers write: “Our results suggest that on-street parking can also help to create a safer environment. While this statement seems to contradict most of the existing research, the reality is that lower speed roads (less than 35 mph) with on-street parking have far less severe and fatal crashes. In fact, lower speed streets without parking had a severe and fatal crash rate more than two times higher than the streets with parking. We also showed conclusively that drivers tended to travel slower in the presence of features such as on-street parking and small building setbacks. Slower vehicle speeds provide pedestrians, cyclists, and drivers more time to react, and when a crash does occur, the chance of it being life-threatening is greatly reduced.” See Wesley Marshall, Norman Garrick, and Gilbert Hansen, “Reassessing On-Street Parking,” paper presented at the Transportation Research Board meeting, January 2008, Washington, D.C.

“roadside conditions”: Richard F. Weingroff, “President Dwight D. Eisenhower and the Federal Role in Highway Safety” (Washington, D. C.: Federal Highway Administration, 2003), retrieved at

they felt it was safer: N. J. Ward and G. J. S. Wilde, “Driver Approach Behaviour at an Unprotected Railway Crossing Before and After Enhancement of Lateral Sight Distances: An Experimental Investigation of a Risk Perception and Behavioural Compensation Hypothesis,” Safety Science, vol. 22 (1996), pp. 63-75.

raise property values: See, for example, S. E. Maco and E. G. McPherson, “A Practical Approach to Assessing Structure, Function, and Value of Street Tree Populations in Small Communities,” Journal of Arboriculture, vol. 29, no. 2 (March 2003).

from roadsides for decades: In a 1941 Chicago planning study titled Subdivision Regulation, for example, the author, Harold Lautner, wrote: “While it has been customary in the past to plant street trees between the street curb and the pedestrian walk, an alternate procedure is now recommended as preferable in some cases. Trees planted along the street curb increase the severity of motor accidents and in turn are easily subjected to traffic injury…and except on very wide streets, curb planted trees crowd in upon the traveled way. To plant street trees on the property side of pedestrian walks, away from the pavement and traffic, seems more desirable, particularly on residential streets” (emphasis in original). This would, of course, not only increase the speed of passing traffic, posing more of a risk to pedestrians, but would also remove a potential barrier to a car striking a pedestrian. From Southworth and Ben-Joseph, Streets and the Shaping of Towns and Cities, op. cit., p. 88.

Chapter Eight: How Traffic Explains the World

same space as New York City: This figure is taken from Richard L. Forstall, Richard P. Green, and James B. Pick, “Which Are the Largest: Why Published Populations for Major Urban Areas Vary So Greatly.” Accessed from the University of Illinois-Chicago “City Futures” conference Web site,

same lane as the cyclists: Dinesh Mohan, The Road Ahead: Traffic Injuries and Fatalities in India (New Delhi: Transportation Research and Injury Prevention Programme, Indian Institute of Technology; 2004), pp. 1-30.

but before: Lu Huapu, Shi Qixin, and Masato Iwasaki, “A Study on Traffic Characteristics at Signalized Intersections in Beijing and Tokyo,” Tsinghua University, Proceedings of EASTS (The 2nd Conference of the Eastern Asia Society for Transportation Studies).

would mean “stop”: This story is discussed in Keesing’s Research Report, The Cultural Revolution in China (New York: Scribner, 1967), p. 18.

“can he actually overtake”: Kenneth Tynan, The Diaries of Kenneth Tynan (New York: Bloomsbury, 2002), p. 101.

the entire street: The journalist Jan Wong, writing about Beijing in the 1980s, reported that “even state-owned cars were so rare that most Beijing intersections lacked traffic lights. Stop signs were non-existent. At night, cars were required to douse headlights to avoid blinding cyclists. With only a handful of vehicles on the road, no one worried about one car smashing into another in the dark.” See Jan Wong’s China (Toronto: Doubleday Canada, 1999), p. 212.

as a social good?: For a good discussion of Mao’s “lawlessness” concept, see Chapter 10 of Zhengyuan Fu, Autocratic Tradition and Chinese Politics (Cambridge: Cambridge University Press, 1993).

public morality and civic culture: See, for example, Wen-shun Chi, Ideological Conflicts in Modern China: Democracy and Authoritarianism (New York: Transaction Publishers, 1986), p. 56.

“superior to them”: This quote comes from “Moral Embarrassment,” Shanghai Star, August 11, 2001.

“rights by litigation”: Albert H. Y. Chen, “Toward a Legal Enlightenment: Discussions in Contemporary China on the Rule of Law,” UCLA Pacific Basin Law Journal, vol. 17 (2000).

drive on the right: The information about which side of the road different countries drive on was obtained from Peter Kincaid’s exhaustive treatise The Rule of the Road: An International Guide to History and Practice (New York: Greenwood Press, 1986).

violation of the standard: The flashing of headlights in Europe also seems to be bluntly effective at getting people to move over. As a study of Austrian highway behavior showed, while demographic factors explained which drivers tended to drive faster and tailgate more aggressively (men driving expensive cars, as you might expect), there was also what the author called an “instrumental function”—the urge to “dominate” other drivers seemed to be the most effective way to encourage them to move over. “It was found that drivers who approach to under ten meters behind the camera car were more likely to displace the driver ahead,” the authors wrote. “Furthermore, drivers who approached faster displaced others more effectively.” Klaus Atzwanger and B. Ruso, in Vision in Vehicles VI (Amsterdam: Elsevier Science B.V., 1999), p. 197.

confusing array of laws: See, for example, the Web site maintained by John Carr,

rights have been violated: George McDowell, an economist at Virginia Tech, has offered the fascinating theory that a country’s traffic behavior is reflected in its economic system. In the United States, the supposed “free market” is, he argues, instead an “open market,” in which “rules, both formal and informal, govern behavior. Opportunistic behavior is expected and even encouraged but within a strict set of parameters.” In China, however, he argues, the system is better described as a “free market,” where “the only rule is caveat emptor.” The Chinese system of what he calls “advantage” means that horns are used less as a means to signal “road rage” but more to “notify other vehicles that you are there and will not give way.” Advantage “is gained,” he writes, “exploited by the person who gained it, and accepted by the person bested.” In the United States this acceptance is less likely to occur. See George R. McDowell, “The Market as Traffic: An Economic Metaphor,” Journal of Economic Issues, vol. 38 (2004), pp. 270-74.

acts more personally: American roads are also more crowded than the expensive Italian autostrada. This brings up the issue that it may be more difficult for drivers to “get over” and meet the demands of the driver to the rear; there is also the larger issue that giving up an entire lane to a few people wishing to go fast, with all the lane changing that entails, can be poor use of the traffic network.

fairness and equality: According to the political scientist Robert Putnam, this dynamic is more prevalent in the southern regions of Italy. These, he argued, have historically lacked a strong civic culture, being dominated instead by feudalistic patronage relationships and an “amoral familism”—worry about yourself and trust that everyone will look after themselves. Instead of “horizontal” networks of reciprocal relations and trust among the community, Putnam argues, the south has been dominated by more vertical, patron-client-style relationships. From Robert Putnam, Making Democracy Work: Civic Traditions in Modern Italy (Princeton: Princeton University Press, 1993).

jaywalking: The historian Peter Norton, in an exemplary article, traces the etymology of the word to at least 1909, well before the 1917 Boston usage registered by the second edition of the Oxford English Dictionary in 1989. Norton traces the rise of the word in the popular imagination as pedestrians saw gradually eroded their longstanding right to a shared use of city streets, in favor of a historically unprecedented edict, as described by one writer, upon the arrival of the automobile: “The streets are for vehicle traffic, the sidewalks for pedestrians.” Jaywalking, in essence, marginalized and even criminalized what had been standard urban behavior. This was done ostensibly in the name of safety, but as Norton notes, its real aim was to clear urban streets for the increased circulation of vehicular traffic (other, potentially more effective, safety measures like speed “governors” for cars were overridden by motoring interests). Peter D. Norton, “Street Rivals: Jaywalking and the Invention of the Motor Age Street,” Technology and Culture, vol. 48 (April 2007), pp. 331-59.

in which he was raised: Aksel Sandemose, A Fugitive Crosses His Tracks (New York: Alfred A. Knopf, 1936).

rules of grammar: Sanford W. Gregory Jr. compared traffic behavior in Egypt to a “verdant grammar,” one not “yet ripened by centuries of social-interactive maturation.” The arrival of mass driving in Egypt, he suggests, happened too quickly for Western traffic patterns to be institutionalized, so instead a kind of pidgin or creole language was formed, with distinct rules, as is often the case “when mature speakers of diverse dominant language groups meet.” Without time to create a formal order of its own, Egypt’s drivers invented a brutally effective slang of sorts. Gregory commented that this seemed based more on eye contact and informal signals than in the West. See Gregory, “Auto Traffic in Egypt as a Verdant Grammar,” Social Psychology Quarterly, vol. 48, No. 4 (December 1985), pp. 337-48.

each side of the street: This story is mentioned in William Muray, City of the Soul: A Walk in Rome (New York: Crown, 2003), p. 26.

Mythological status: H. V. Morton, in his 1957 travelogue A Traveler in Rome, observed, while riding in a taxi: “The cars around us, which were traveling just as fast as we were, swerved aside by one of those instinctive Italian motoring movements not unlike birds in formation who part and form again” (1957; repr., New York: Da Capo, 2002), p. 135.

one-fifth of the traffic: Michele Faberi, Marco Martuzzi, and Franco Pirrami, Assessing the Health Impact and Social Costs of Mopeds: Feasibility Study in Rome (Rome: World Health Organization, 2004), p. xvii.

fewer riders wear helmets: The helmet-use rates come from F. Servadei, C. Begliomini, E. Gardini, M. Giustini, F. Taggi, and J. Kraus, “Effect of Italy’s Motorcycle Helmet Law on Traumatic Brain Injuries,” Injury Prevention, vol. 9, no. 3 (2003), pp. 257-60.

collisions with cars: Giuseppe Latorre, Giuliano Bertazzoni, Donato Zotta, Edward Van Beeck, and Gualtiero Ricciardi, “Epidemiology of Accidents Among Users of Two-Wheeled Motor Vehicles: A Surveillance Study in Two Italian Cities,” European Journal of Public Health, vol. 12, no. 2 (2002), pp. 99-103.

(and getting away with it): R. B. Cialdini, L. J. Demaine, B. J. Sagarin, D. W. Barrett, K. Rhoads, and P. L. Winter, “Managing Social Norms for Persuasive Impact,” Social Influence, vol. 1 (2006), pp. 3-15.

behavior either way: There have been several studies of jaywalking and model behavior. See, for instance, Monroe Lefkowitz, Robert R. Blake, and Jane Srygley Mouton, “Status Factors in Pedestrian Violation of Traffic Signals,” Journal of Abnormal and Social Psychology, vol. 51 (1955), pp. 704-06, and Brian Mullen, Carolyn Copper, and James E. Driskell, “Jaywalking as a Function of Model Behavior,” Personality and Social Psychology Bulletin, vol. 16, no. 2 (1990), pp. 320-30.

are famously orderly: Joe Moran makes the point that people in England have been “complaining about the disintegration of queue discipline for almost as long as they have been lauding the queue as the essence of British decency—perhaps because this myth carries such symbolic weight that it cannot be sustained by the necessarily messier reality.” From Joe Moran, Queuing for Beginners (London: Profile Books, 2007), p. 92.

more in theory than reality: Liu Shinan argues that Chinese do queue up when queuing itself is the norm: “We queue where we are accustomed to queue, for example, at a cinema booking office or at the cashier’s counter in a supermarket. In many places where we are not accustomed to queue, however, we do not queue—for example, in front of an elevator or subway door.” Liu Shinan, “Behavior of Tourists Has No Quick Fix,” China Daily,November 10, 2006.

to be slight: One study found the correlation between “service quality” and tipping to be just 0.07 percent. See Michael Conlin, Ted O’Donohue, and Michael Lynn, “The Norm of Restaurant Tipping,” Journal of Economic Behavior and Organization, vol. 52 (2003), pp. 297-321. For an excellent overview of the quite extensive academic literature on tipping, I recommend the work of Ofer Azar, an economist at Ben-Gurion University of the Negev in Israel, particularly “The Social Norm of Tipping: A Review,” Journal of Applied Social Psychology, vol. 37, no. 2 (2007), pp. 380-402.

“obeying the law”: See Amir Licht, “Social Norms and the Law: Why People Obey the Law,” a working paper available at

to nearly 84,000: Sheng-Yong Wang, Gui-Bo Chi, Chun-Xia Jing, Xiao-Mei Dong, Chi-Peng Wu, and Li-Ping Li, “Trends in Road Traffic Crashes and Associated Injury and Fatality in the People’s Republic of China, 1951-1999,” Injury Control and Safety Promotion, vol. 10, nos. 1-2 (2003), pp. 83-87.

roughly 49 million: New York Times, July 22, 1951.

Smeed’s law: R. J. Smeed, “Some Statistical Aspects of Road Safety Research,” Journal of the Royal Statistical Society, Series A (General), vol. 112, no. 1 (1949), pp. 1-34.

as low as 10 percent: Vinand M. Nantulya and Michael R. Reich, “The Neglected Epidemic: Road Traffic Injuries in Developing Countries,” British Medical Journal, May 2002, pp. 1139-41.

a staggering 80 percent: Mohan, The Road Ahead, op. cit. pp. 1-30.

onto the same thoroughfare: In a discussion paper for the World Bank, Christopher Willoughby notes that “the current problems of motorization seem not generally to result from its occurring at lower per capita income levels, or more rapidly, than in the countries which coped with it reasonably satisfactorily in earlier years; it also grew very fast there for prolonged periods, especially in France (and Germany). The problems tend to be connected rather with the higher concentration of national population, economic activity and motorization itself in one or a very few major cities, at times when those cities are also increasing in size and population much more rapidly than was the case in Europe or Japan.” From Christopher Willoughby, “Managing Motorization,” Discussion Paper TWU-42, World Bank; available at:

nearly 100 percent: For a fascinating discussion of history of automobile insurance in China and recent reforms, see J. Tim Query and Daqing Huang, “Designing a New Automobile Insurance Pricing System in China: Actuarial and Social Considerations,” Casualty Actuarial Society Forum, Winter 2007.

to West Germany’s 130: Flaura K. Winston, Craig Rineer, Rajiv Menon, and Susan P. Baker, “The Carnage Wrought by Major Economic Change: Ecological Study of Traffic Related Mortality and the Reunification of Germany,” British Medical Journal, vol. 318 (June 19, 1999), pp. 1647-50.

begin to accelerate: See Richard Dahl, “Heavy Traffic Ahead: Car Culture Accelerates,” Environmental Health Perspectives, April 2005.

Maureen Cropper shows: Elizabeth Kopits and Maureen Cropper, “Traffic Fatalities and Economic Growth,” Accident Analysis & Prevention, vol. 37 (2005), pp. 169-78.

terms of traffic safety: Based on statistics from the International Traffic Safety Data and Analysis Group; retrieved on January 13, 2007, from

some 160 deaths per 10,000 vehicles: World Report on Road Traffic Injury Prevention (Geneva: World Health Organization and World Bank, April 4, 2004).

“to use the buses”: BBC, February 28, 2001. Accessed from:

slightly higher in Belgium): Pocket World in Figures 2007 (London: Economist, 2007).

risk of traffic fatalities: See Theodore E. Keeler, “Highway Safety, Economic Behavior, and Driving Environment,” American Economic Review, vol. 84, no. 3 (1994), pp. 684-93, and Reid Ewing, Richard A. Schieber, and Charles V. Zegeer, “Urban Sprawl as a Risk Factor in Motor Vehicle Occupant and Pedestrian Fatalities,” American Journal of Public Health, vol. 93, no. 9 (2003), pp. 1541-45.

Belgium had 522: World Report on Road Traffic Injury Prevention, op. cit., p. 198.

fairness of the process: Tom R. Tyler, Why People Obey the Law (Princeton, N.J.: Princeton University Press, 2006).

The information on Belgium’s traffic enforcement comes from Lode Vereeck and Lieber Deben, “An International Comparison of the Effectiveness of Traffic Safety Enforcement Policies,” unpublished paper, Limburg University, Belgium, 2003.

lowest crash rates in the world: Retrieved from the International Road Traffic and Accident Database (IRTAD), at

after-tax income: Before 1999, fines were based on pretax income, says Heikki Summala of the Traffic Research Unit at the University of Helsinki. This means fines have dropped between 20 and 60 percent, but at the same time minimum fines were raised, so revenue has in fact increased. E-mail correspondence with Heikki Summala, November 9, 2007.

Jaakko Rytsölä: The Finnish speeding ticket information comes from Steve Stecklow, “Finnish Drivers Don’t Mind Sliding Scale, but Instant Calculation Gets Low Marks,” Wall Street Journal, January 2, 2001.

return to shortly: A Finnish public-opinion poll in 2001 found that 66 percent of male drivers and 73 percent of male nondrivers felt the fine system was fair, while 77 percent of female drivers and 78 percent of female nondrivers thought it fair. The data comes from a study (in Finnish): T. Lappi-Seppälä, “Public Opinion and the 1999 Reform of the Day-Fine System,” National Research Institute of Legal Policy, Publication No. 195, Helsinki, 2002. Thanks to Heikki Summala for providing the numbers.

rather stagnant: In 2003, for example, according to Eurostat, it grew just .50 percent. Data obtained from Had the GDP risen, there may have been an increase in fatalities, reflecting the higher amounts of driving due to economic vitality—but it certainly would not have been by enough to offset the huge reductions in fatalities.

been in a crash): E. Lagarde, M. Chiron, and S. Lafont. “Traffic Ticket Fixing and Driving Behaviours in a Large French Working Population,” Journal of Epidemiology and Community Health, vol. 58 (2004), pp. 562-68.

hundreds of traffic fatalities: Alexandre Dorozynski, “French Elections Can Kill,” British Medical Journal, November 3, 2001, p. 1021.

The lesson is: At least one analysis posits that income equality is related in a linear fashion to traffic fatalities; e.g., in both poor, and, to a lesser extent, wealthy countries, the traffic fatality rate may be affected by the level of income equality. Perhaps not surprisingly, the Scandinavian countries, among the leaders in income equality, also rank near the top in traffic safety. See Nejat Anbarci, Monica Escaleras, and Charles Register, “Income, Income Inequality and the ‘Hidden Epidemic’ of Traffic Fatalities,” No. 5002, Working Papers from Department of Economics, College of Business, Florida Atlantic University. Retrieved from

and traffic fatalities: This relationship is argued in, among other sources, D. Treisman, “The Causes of Corruption: A Cross-National Study,” Journal of Public Economics, no. 76 (June 2000), pp. 399-457.

income and traffic fatalities: See Nejat Anbarci, Monica Escaleras, Monica Register, and Charles A. Register, “Traffic Fatalities and Public Sector Corruption,” Kyklos, vol. 59, no. 3 (August 2006), pp. 327-44; available at

of Europe’s road fatalities: See “Fools and Bad Roads,” Economist, March 22, 2007.

rewards inefficient firms: For a good review of the various debates over corruption and growth, see P. Bardhan, “Corruption and Development: A Review of Issues,” Journal of Economic Literature, vol. 35 (September 1997), pp. 1320-46.

beneath the acceptable “minimum”: See Daniel Kaufmann, “Corruption: The Facts,” Foreign Policy, no. 107 (Summer 1997), pp. 114-31.

because of corruption: The most extreme case of this may be Lagos, the largest city in Nigeria and predicted to be among the world’s largest cities in the next decade. The average commuter in Lagos is said to face myriad challenges. These begin with the crumbling roads and infrastructure, which have scarcely been repaired since being erected in the oil boom of the 1970s; they themselves are a kind of symbol of the endemic corruption of Nigeria, where close to $400 billion in oil revenues were sequestered out of the country in a forty-year period. Other challenges include arbitrary fees charged at will by bus drivers and their quasi-official associates, the agberos, not to mention the numerous unofficial roadblocks, manned by gangs of unemployed “area boys,” that drivers must navigate. The multiple levels of corruption present in—and contributing to—Lagos’s epic “go-slows” were demonstrated in an astonishing story told by the journalist George Packer. While riding on the streets of Lagos, Packer’s driver was stopped by an agbero, who demanded money to help the driver negotiate another bribe, with the official traffic police. The traffic cop intervened, if only to collect the bribe—not doing so, it seemed, would actually make the police officer look as if he were derelict in his duty. See George Packer, “The Megacity: Decoding the Chaos of Lagos,” New Yorker, November 26, 2006. See also Adewale Ajayi, Nigerian Tribune, March 2, 2007; and Osise Dibosa, “Olubunmi Peters and Ferma,” This Day, June 12, 2007.

take their place: Benjamin A. Olken and Patrick Barron, “The Simple Economics of Extortion: Evidence from Trucking in Aceh,” NBER Working Paper No. 13145, National Bureau of Economic Research, June 2007.

“work repairing potholes”: Robert Guest, “The Road to Hell Is Unpaved,” Economist, December 19, 2002.

“actual driving skill”: The Delhi driving-license experiment is detailed in Marianne Bertrand, Simeon Djankov, Rema Hanna, and Sendhil Mullainathan, “Does Corruption Produce Unsafe Drivers?” NBER Working Paper No. 12274, National Bureau of Economic Research, June 2006.

“clarity of purpose”: This line comes from Pavan K. Varma, Being Indian (London: Penguin Books, 2005), p. 79.

some 150,000 tickets: Raymond J. Fisman and Edward Miguel, “Cultures of Corruption: Evidence from Diplomatic Parking Tickets,” NBER Working Paper No. W12312 (June 2006). Retrieved at

the city of London: Retrieved from Channel Four News Online, tops+45m/569892.

pays the charge: Nicola Woolcock, “Nations Unite to Join a Boycott of Congestion Charge,” Times (London), February 21, 2007.

norms regarding them: This is why we can often see compliance with traffic laws differing even within a country. In Italy, corruption is more endemic in the south than the north, for reasons, as mentioned in an earlier note, having to do with varying degrees of civic culture. And so as the state seems to gradually wither away the farther south you go, so too does the traffic behavior come to have less to do with the law. In 2000, a national helmet law was passed for motorcyclists of any age. Afterward, usage rates in the north were reported as high as 95 percent. In the south, however, they were only as high as 70 percent, and as low as 50 percent. For corruption levels, see Alfredo del Monte and Erasmo Papagni, “The Determinants of Corruption in Italy: Regional Panel Data Analysis,” European Journal of Political Economy, vol. 23 (June 2007), pp. 379-96. For helmet-use rates, see F. Servadei, C. Begliomini, E. Gardini, M. Giustini, F. Taggi, and J. Kraus, “Effect of Italy’s Motorcycle Helmet Law on Traumatic Brain Injuries,” Injury Prevention, vol. 9, no. 3 (2003), pp. 257-60.

casualties there will be: See D. Parker, J. T. Reason, A. S. R. Manstead, and S. G. Stradling, “Driving Errors, Driving Violations and Accident Involvement,” Ergonomics, vol. 38 (1995), pp. 1036-48.

more women in government: Anand Swamy, Stephen Knack, Young Lee, and Omar Azfar, “Gender and Corruption,” Center for Development Economics, Department of Economics, Williams College, 2000.

Chapter Nine: Why You Shouldn’t Drive with a Beer-Drinking Lawyer

our brains as we drive: Research has shown that the various aspects of driving, everything from following a traffic rule (e.g., specifying a one-way street) to navigating a set of directions to anticipating the actions of other drivers, seem to trigger discrete activity in a variety of brain regions and networks. Researchers at University College London, for example, have monitored drivers as they “drove” the detailed recreation of London found in the popular video game The Getaway. See H. J. Spiers and E. A. Maguire, “Neural Substrates of Driving Behaviour,” NeuroImage, vol. 36 (2007), pp. 245-55.

fifty thousand times a year: P. G. Martin and A. L. Burgett, “Rear-End Collision Events: Characterization of Impending Crashes,” Proceedings of the First Human-Centered Transportation Simulation Conference (Iowa City: University of Iowa, 2000).

walks away alive: See Jack Stuster, “The Unsafe Driving Acts of Motorists in the Vicinity of Large Trucks,” U.S. Department of Transportation, Federal Highway Administration, Office of Motor Carriers and Highway Safety, February 1999.

should probably fear: See L. J. Armony, D. Servan-Schreiber, J. D. Cohen, and J. E. LeDoux, “An Anatomically-Constrained Neural Network Model of Fear Conditioning,” Behavioral Neurocience, vol. 109 (1995), pp. 246-56.

dangerous nature of trucks: Opinion surveys of car drivers tend to find mostly negative opinions of truck drivers’ behavior. See, for example, Robert S. Moore, Stephen LeMay, Melissa L. Moore, Pearson Lidell, Brian Kinard, and David McMillen, “An Investigation of Motorists’ Perceptions of Trucks on the Highways,” Transportation Journal, January 5, 2001.

responsibility in the crash: Daniel Blower, “The Relative Contribution of Truck Drivers and Passenger Vehicles to Truck-Passenger Vehicle Traffic Crashes,” report prepared for the U.S. Department of Transportation, Federal Highway Administration, Office of Motor Carriers, June 1998.

is actually the case): This may be the “availability heuristic” at work again. Large trucks, in part because they are driven longer distances and tend to be on the road at the same time as most motorists, seem to be more prevalent than they really are. A Canadian study found that while motorists believed that the number of trucks on the roads was rising, the number actually dropped during the period in question (while the number of cars grew). See Gordon G. Baldwin, “Too Many Trucks on the Road?” Transportation Division, Statistics Canada, Ottawa.

“risk as analysis”: Paul Slovic, Melissa L. Finucane, Ellen Peters, and Donald G. MacGregor, “Risk as Analysis and Risk as Feelings: Some Thoughts About Affect, Reason, Risk, and Rationality,” Risk Analysis, vol. 24, no. 2 (2004), pp. 311-23.

50 years of driving: Data retrieved on May 5, 2007, from

the lifetime probability: P. Slovic, B. Fischhoff, and S. Lichtenstein, “Accident Probabilities and Seat Belt Usage: A Psychological Perspective,” Accident Analysis & Prevention, vol. 13 (1978), pp. 281-85.

“the danger of leaving home”: William H. Lucy, “Mortality Risk Associated with Leaving Home: Recognizing the Relevance of the Built Environment,” American Journal of Public Health, vol. 93, no. 9 (September 2003), pp. 1564-69.

eleven times that: This figure was provided to me by Per Garder, a professor of civil and environmental engineering at the University of Maine. Using the required risk exposure levels as quoted by the Occupational Safety and Health Administration (in “Occupational Exposure to Asbestos,” Federal Register 59:40964-41161, 1994, and OSHA Preambles, “Blood Borne Pathogens,” 29 CFR 1910.1030, Federal Register 56:64004, 1991: 29206), Garder notes that the risk of dying over a lifetime in manufacturing and service employment, respectively, “must be less than 1. 8 and 1.0 deaths per 1,000 employees.” By those standards, Garder extrapolates if 1 person in a 1,000 were “allowed” to die in traffic over an average of 77 years of life, 1 person in 77,000 would thus be allowed to die in America this year in a traffic accident. Using America’s population of 300 million, 1 in 77,000 would be 3,896 people. But the fatality figure was over 11 times that. In other words, if traffic were an industry—whether heavy manufacturing or service—it would have been shut down a long time ago.

every thirty-two minutes: Fatality statistics were taken from Traffic Safety Facts 2004 (Washington, D.C.: National Highway Traffic Safety Administration, 2005).

3 out of every 1,000: Clifford Winston, Vikram Maheshri, and Fred Mannering, “An Exploration of the Offset Hypothesis Using Disaggregate Data: The Case of Airbags and Antilock Brakes,” Journal of Risk Uncertainty, vol. 32 (2006), pp. 83-99.

raises the crash risk: M. G. Lenné, T. J. Triggs, and J. R. Redman, “Time of Day Variations in Driving Performance,” Accident Analysis & Prevention, vol. 29, no. 4 (1997), pp. 431-37, and G. Maycock, “Sleepiness and Driving: The Experience of U.K. Car Drivers,” Accident Analysis & Prevention, vol. 29, no. 4 (1997), pp. 453-62.

day to be on the road: As David Klein and Julian Waller noted, the posting of holiday traffic fatalities presents several problems. “Although absolute numbers may serve a purpose in indicating the raw impact of highway crashes on the nation or on a community,” they write, “their use provides only a partial indication of magnitude and often a misleading indication of trends. First, fatality figures ignore the 1. 5 to 3 million annual non-fatal injuries—which may represent a social cost far higher than the 56,000 fatalities. Second, the ‘holiday death toll’ may give drivers an unjustified feeling of anxiety on holiday weekends and a false sense of security on weekdays if it persuades them that the holiday incidence is substantially higher than on weekdays.” From Klein and Waller, “Causation, Culpability and Deterrence in Highway Crashes,” prepared for the Department of Transportation, July 1970, p. 27.

week before or after: C. M. Farmer and A. F. Williams. “Temporal Factors in Motor Vehicle Crash Deaths,” Injury Prevention, vol. 2 (2005), pp. 18-23.

should be about $8,000: Steven D. Levitt and Jack Porter, “How Dangerous Are Drinking Drivers?,” Journal of Political Economy, vol. 109, no. 6 (2001), pp. 1198-1237. The authors rely on a clever statistical trick that does not require knowing the actual number of drinking and sober drivers on the road (a number that would be extremely hard to come by in any case) but, rather, uses an extrapolation taken from the relative proportion of sober and drunk drivers involved in two-car crashes. Levitt and Porter generate their relative risk numbers by looking at two-car crashes and “the relative frequency of accidents involving two drinking drivers, two sober drivers, or one of each.” This information, they argue, “is sufficient to separately identify both the relative likelihood of causing a fatal crash on the part of drunk and sober drivers and the fraction of drivers on the road who have been drinking.”

doubling of the speed: H. C. Joksch, “Velocity Change and Fatality Risk in a Crash: A Rule of Thumb,” Accident Analysis & Prevention, vol. 25, no. 1 (1993), pp. 103-04.

doing 30 miles per hour: Allan F. Williams, Sergey Y. Krychenko, and Richard A. Retting, “Characteristics of Speeders,” Journal of Safety Research, vol. 37 (2006), pp. 227-32.

get into more crashes: See, for example, Williams, Kyrychenko, and Retting. “Characteristics of Speeders,” ibid.

additional 5 kilometers per hour: See C. N. Kloeden, A. J. McLean, V. M. Moore, and G. Ponte, “Travelling Speed and the Risk of Crash Involve ment,” NHMRC Road Accident Research Unit, University of Adelaide, November 1997.

“relatively high speed drivers”: David Solomon, Accidents on Main Rural Highways Related to Speed, Driver, and Vehicle (Washington, D.C.: U.S. Department of Commerce, Bureau of Public Roads, 1964).

flow in smooth harmony: The speed-variance argument was most famously taken up by Charles Lave, “Speeding, Coordination, and the 55 MPH Limit,” American Economic Review, vol. 75, no. 5 (December 1985), pp. 1159-64. Interestingly, in a point that has not been emphasized by those later citing Lave, he writes: “Although I have found no statistically discernible effect from speed, per se, this does not necessarily imply that it is safe to raise the speed limit, for we do not know what effect a higher limit would have on the speed variance.” If the speed limit is 65 miles per hour but many people are driving 75, it does not necessarily follow that raising it to 75 miles per hour will reduce speed variance or make things safer. Do we want the drivers who feel comfortable at a lower level forced to go faster? Do we want Grandma and Grandpa driving 75 miles per hour?

held by young males: T. Horberry, L. Hartley, K. Gobetti, F. Walker, B. Johnson, S. Gersbach, and J. Ludlow, “Speed Choice by Drivers: The Issue of Driving Too Slowly,” Ergonomics, vol. 47, no. 14 (November 2004), pp. 1561-70.

at low speeds: For elaboration on this point, see Kloeden, McLean, Moore, and Ponte, “Travelling Speed,” op. cit.

involved a stopped vehicle: Ronald K. Knipling, “IVHS Technologies Applied to Collision Avoidance: Perspectives on Six Target Crash Types and Countermeasures,” technical paper presented at the Safety and Human Factors session of 1993 IVHS America Annual Meeting, Washington, D.C., April 14-17, 1993.

not hold for individuals: Gary A. Davis, “Is the Claim That ‘Variance Kills’ an Ecological Fallacy?,” Accident Analysis & Prevention, vol. 34 (2002), pp. 343-46. With the Solomon curve, Davis argues that one cannot determine the individual driver’s crash risk by looking at the whole. Solomon’s curve, maintains Davis, is a purely mathematical effect that says little about how the world works, “like saying an object is heavy because it weighs more.” Another problem with the Solomon curve is that it does not explain causes. If twenty cars slowing for traffic congestion—and thus going below the median speed—were struck by ten cars traveling at the median and ten cars traveling above the median, the resulting “curve” would indeed suggest that slower drivers were the most at risk of being in a crash. But looking at each crash individually, one would conclude that the faster-moving cars had actually been the source of the risk for the slower-moving cars. As an example of a ecological fallacy, the statistician David Freedman has compared the income levels of U.S. states against the percentage of foreign-born residents in each. Doing this, one could make a statistically robust “correlation” that says foreign-born residents of the United States earn more than native-born residents, when actually the opposite is true. See David A. Freedman, “Ecological Inference and the Ecological Fallacy,” in International Encyclopedia of the Social & Behavioral Sciences, vol. 6, ed. N. J. Smelser and Paul B. Baltes (New York: Pergamom, 2001), pp. 4027-30.

in the same direction: E. C. Cerrelli, “1996 Traffic Crashes, Injuries, and Fatalities—Preliminary Report,” Report No. DOT HS 808 543, National Highway Traffic Safety Administration, March 1997. I was alerted to this finding by an excellent report summarizing the various speed issues. See Jack Stuster and Zail Coffman (1998), Synthesis of Safety Research Related to Speed and Speed Limits, FHWA-RD-98-154 (Washington, D.C.: Federal Highway Administration, 1998).

whose teams had lost: D. A. Redelmeier and C. L. Stewart, “Do Fatal Crashes Increase Following a Super Bowl Telecast?” Chance, vol. 18, no. 1 (2005), pp. 19-24.

have been drinking: R. G. Smart, “Behavioral and Social Consequences Related to the Consumption of Different Beverage Types,” Journal of Studies on Alcohol, vol. 57 (1996), pp. 77-84.

at .08 to .1 percent: R. P. Compton, R. D. Blomberg, H. Moskowitz, M. Burns, R. C. Peck, and D. Fiorentino, “Crash Risk of Alcohol Impaired Driving,” Proceedings of the 16th International Conference on Alcohol, Drugs and Traffic Safety, CD-ROM (Montreal, Société de l’Assurance Automobile du Québec, 2002).

BAC of zero: R. F. Borkenstein, R. F. Crowther, R. P. Shumate, W. B. Ziel, and R. Zylman, “The Role of the Drinking Driver in Traffic Accidents,” Bloomington, Indiana, Department of Police Administration and Indiana University, 1964.

“handling” a small intake: See, for example, Leonard Evans, Traffic Safety (Bloomfield Hills: Science Serving Society, 2004), p. 246.

shown up in other studies: P. L. Zador, S. A. Krawchuk, and R. B. Voas, Relative Risk of Fatal and Crash Involvement by BAC, Age and Gender (Rockville, Md.: Westat, April 2000).

statistically less safe: Paul M. Hurst, David Harte, and William Frith, “The Grand Rapids Dip Revisited,” Accident Analysis & Prevention, vol. 26, No. 5 (1994), pp. 647-54.

ratio is even higher: Evans, Traffic Safety, op. cit., p. 44.

the rate is .36: David Gerard, Paul S. Fischbeck, Barbara Gengler, and Randy S. Weinberg, “An Interactive Tool to Compare and Communicate Traffic Safety Risks: Traffic STATS,” Center for the Study and Improvement of Regulation, Carnegie Mellon University, Transportation Research Board 07-1332, November 2006.

to prove that they are: They also kill others more often. A study in the United Kingdom found, for example, that pedestrians were roughly 1.5 times more likely to die when they were hit by a male driver than a female driver. Car Make and Model: The Risk of Driver Injury and Car Accident Rates in Great Britain: 1994, Transport Statistics Report (London: HMSO, 1995).

more likely to drink: National Institute on Alcohol Abuse and Alcoholism. “Drinking in the United States: Main Findings from the 1992 National Longitudinal Alcohol Epidemiologic Survey (NLAES),” U.S. Alcohol Epidemiologic Data Reference Manual, vol. 6 (Bethesda, Md.: National Institute of Health, 1998).

less likely to wear helmets: C. Peek-Asa and J. F. Kraus, “Alcohol Use, Driver, and Crash Characteristics Among Injured Motorcycle Drivers, Journal of Trauma, vol. 41 (1996), pp. 989-93.

those who are sober: See, for example, R. D. Foss, D. J. Beirness, and K. Sprattler, “Seat Belt Use Among Drinking Drivers in Minnesota,” American Journal of Public Health, vol. 84, no. 11 (1994), pp. 1732-37.

attributed to the driver: Emmanuel Lagarde, Jean-François Chastang, Alice Gueguen, Mireille Coeuret-Pellicer, Mireille Chirion, and Sylviane Lafont, “Emotional Stress and Traffic Accidents: The Impact of Separation and Divorce,” Epidemiology, vol. 15, no. 6 (November 2006).

and gender differences): G. Whitlock, R. Norton, T. Clark, R. Jackson, and S. MacMahon, “Motor Vehicle Driver Injury and Marital Status: A Cohort Study with Prospective and Retrospective Driver Injuries,” Injury Prevention,vol. 10 (2004), pp. 33-36.

Spain to California: See, for example, T. Reuda-Domingo and P. Lardelli-Claret, “The Influence of Passengers on the Risk of the Driver Causing a Car Collision in Spain: Analysis of Collisions from 1990 to 1999,” Accident Analysis & Prevention, vol. 36 (2004), pp. 481-89, and Judy A. Geyer and David R. Ragland, “Vehicle Occupancy and Crash Risk,” UCB-TSC-RR-2004-16, Berkeley, Institute of Transportation Studies, 2004; paper accessed at

if there’s a passenger: Actually, if one is involved in a crash, a passenger is still a good bet. The added mass, it has been suggested, could reduce a driver’s fatality risk in a frontal collision by 7. 5 percent. See Leonard Evans, “Causal Influence of Car Mass and Size on Driver Fatality Risk,” American Journal of Public Health, vol. 91, no. 7 (July 2001), pp. 1076-81.

passengers in the car: Geyer and Ragland, “Vehicle Occupancy,” op. cit.

with passengers onboard: Li-Hui Chen, Susan P. Baker, Elisa R. Braver, and Guohua Li, “Carrying Passengers as a Risk Factor for Crashes Fatal to 16-and 17-Year-Old Drivers,” Journal of the American Medical Association, vol. 283 (2000), pp. 1578-82.

held for female drivers): B. G. Simons-Morton, N. Lerner, and J. Singer, “The Observed Effects of Teenage Passengers on Risky Driving Behavior of Teenage Drivers,” Accident Analysis & Prevention, vol. 37 (2005), pp. 973-82.

their male comrades: Ronald Kotulak, “Increase in Women Doctors Changing the Face of Medicine,” Jerusalem Post, August 2, 2007.

alcohol-related fatal crash: Information on crashes in Montana and New Jersey is drawn from Rajesh Subramanian, “Alcohol-Related Fatalities and Fatality Rates by State, 2004-2005,” DOT HS 810 686, National Highway Traffic Safety Administration, December 2006: available at

found on rural roads: Growing Traffic in Rural America: Safety, Mobility and Economic Challenges in America’s Heartland (Washington, D.C.: Road Information Program, March 2005).

any other road: ibid.

(nearly 75 percent in 2005): Chicago Tribune, January 12, 2005.

or even while driving: Laura K. Barger, Brian E. Cade, Najib F. Aya, et al., “Extended Work Shifts and the Risk of Motor Vehicle Crashes Among Interns,” New England Journal of Medicine, vol. 352, no. 2 (January 13, 2005).

vehicle on the road: This does not have to do entirely with the vehicle, of course. As Charles Kahane of the National Highway Traffic Safety Administration points out, pickup trucks, at least historically, have tended to be driven more often in rural environments and more often by men—two risk-inflating variables. See Charles J. Kahane, “Vehicle Weight, Fatality Risk and Crash Compatibility of Model Year 1991-99 Passenger Cars and Light Trucks,” National Highway Traffic Safety Administration Report DOT HS 809 662, October 2003.

other kind of vehicle: See, for example, Gerard, Fischbeck, Gengler, and Weinberg, “An Interactive Tool,” op. cit.

pickups also impose: Several hundred people per year in the United States are also killed riding in the unprotected cargo beds of pickup trucks. See C. L. Anderson, P. F. Agran, D. G. Winn, and S. Greenland, “Fatalities to Occupants of Cargo Areas of Pickup Trucks,” Accident Analysis & Prevention, vol. 32, no. 4 (2000), pp. 533-40.

on drivers of other vehicles: See Marc Ross and Tom Wenzel, “The Effects of Vehicle Model and Driver Behavior on Risk,” Accident Analysis & Prevention, vol. 37 (2005), pp. 479-94.

more energy in a crash: See Marc Ross, Denna Patel, and Tom Wenzel, “Vehicle Design and the Physics of Traffic Safety,” Physics Today, January 2006, pp. 49-54.

drivers of smaller cars: Leonard Evans, “Mass Ratio and Relative Driver Fatality Risk in Two-Vehicle Crashes,” Accident Analysis & Prevention, vol. 25 (1993), pp. 609-16.

“was maintained very well”: Thanks to Gabriel Bridger for pointing this out. See for results.

in the New Yorker: Malcolm Gladwell, “Big and Bad,” New Yorker, January 12, 2004.

Wenzel have pointed out: Tom Wenzel and Marc Ross, “Are SUVs Really Safer Than Cars? An Analysis of Risk by Vehicle Type and Model,” Lawrence Berkeley National Laboratory Seminar, July 30, 2002, Washington, D.C. Similarly, the Chevrolet Camaro (or Pontiac Firebird) and Chevy Corvette are equally risky to their own drivers, but the Corvette poses less risk to others. The researchers suspect it may be because of the Corvette’s fiberglass body and lower profile, both of which might cause less damage to others.

the statistically safest demographic?: Sometimes the statistics confound expectations. Take the Volvo V70 station wagon and the two-door BMW 3 Series. The first car conjures visions of staid Scandinavian safety and innocuous suburban commuting, while the image of the latter is of a small sports car piloted by the typically aggressive “Beemer” driver. Yet according to the Insurance Institute for Highway Safety, from 2002 through 2005, the U.S. fatality rate (per million registered vehicle years) for both cars was identical. I have no way of qualifying the difference, and there are a raft of potential statistical problems, but this leads to all kinds of speculation: Did the BMW have better crash protection? Was the safer driving of the Volvo owner offset by inferior handling? Perhaps Volvo wagons carried more passengers or logged more miles? Are BMW drivers better drivers? Or was it just a statistical fluke? As Marc Ross remarked to me in an e-mail correspondence, the relatively small number of fatalities in either car means that any variations in how the data is handled can easily throw off the results. There are a host of small factors that can corrupt the data, he explained: “For example, how long was the model in question on the road in the first year. If the model came out early, then the ‘exposure’ to crashes was relatively long in that first year. If the model came out late, the exposure was short in that first year. A different complication is that models that don’t sell so well tend to stay on the dealer’s lot, but some of them get registered [for tax reasons] by the dealer but aren’t being driven while they stay on the lot.” Therefore they have less exposure to traffic risk than might appear.

more than women: See, for example, Pew Research Center, “As the Price of Gas Goes Up, the Nation’s Odometer Slows Down,” August 8, 2006; available at

wear seat belts less often: V. Vasudevan and S. Nambisan, Safety Belt Usage Surveys: Final Project Report (Las Vegas: Transportation Research Center, University of Nevada, Las Vegas, 2006).

trucks without seat belts: Jeremy Diener and Lilliard E. Richardson, “Seat Belt Use Among Rural and Urban Pickup Truck Drivers,” Report 4-2007, Institute of Public Policy, University of Missouri, July 2007.

involved in a fatal crash: See National Highway Traffic Safety Administration, “Alcohol Involvement in Fatal Motor Vehicle Traffic Crashes, 2003,” DOT HS 809 822, March 2005.

versus white ones?: S. Newstead and A. D’Elia, “An Investigation into the Relationship Between Vehicle Colour and Crash Risk,” Monash University Accident Research Centre, Report 263, 2007.

rental cars: In a conversation, Sheila “Charlie” Klauer noted that in the VTTI’s aforementioned 100-car naturalistic study, both younger and older drivers of leased cars were involved in more risky driving events than the owners of private vehicles. “The leased vehicle drivers were involved in just slightly more events than were the private vehicle drivers. It was consistent,” she said. “It’s kind of a rental car phenomenon, that’s what we’re hypothesizing. I think we are all a little bit more reckless when we’re in a rental car than in our own car.” I was unable to find any study in the U.S. that had tackled this question head-on, although the multiplicity of drivers any rental car has and the varieties of exposure would make it difficult to gauge risk. A study in Jordan did report a higher crash rate among rental cars, though this was complicated by the fact that younger drivers (a riskier group to begin with) seemed to be overrepresented among car renters. See Adli H. Al-Balbissi, “Rental Cars Unique Accident Trends,” Journal of Transportation Engineering, vol. 127, no. 2 (March-April 2001), pp. 175-77.

(less regard for life?): Guy Stecklov and Joshua R. Goldstein, “Terror Attacks Influence Driving Behavior in Israel,” Proceedings of the National Academy of Science, vol. 101, no. 40 (2004), pp. 14551-56.

than in the front: Evans, Traffic Safety, op. cit., p. 56.

some 28,500 lives: C. Hunter Sheldon, Journal of the American Medical Association, November 5, 1955.

from seat belts: John Adams notes that from 1970 to 1978, in a sample of major Western countries that adopted seat-belt laws during the period, “the group of countries that had not passed seat-belt laws experienced a greater decrease [in fatalities] than the group that had passed laws.” In the United Kingdom, he writes, the drop in fatalities in 1983, the first full year after the belt law was passed, was “nothing remotely approaching” the predicted decline of one thousand deaths a year. The only segment of fatalities that dropped dramatically, he notes, was fatalities during the “drink-drive hours” of early Saturday and Sunday mornings—in response, he argues, to a stepped-up campaign against drunk driving. The drop in fatalities at other times, he suggests, was no higher than the annual 3 percent decrease already taking place. “No studies have been done to explain why,” he writes, “after the seat-belt law came into effect in Britain, seat belts were so extraordinarily selective in saving the lives of those who are over the alcohol limit and driving between 10 at night and 4 in the morning.” See John Adams, “Britain’s Seat-Belt Law Should Be Repealed,” draft of a paper for publication in Significance, March 2007.

colors would make more sense): R. G. Mortimer, “A Decade of Research in Rear Lighting: What Have We Learned?,” in Proceedings of the Twenty-first Conference of the American Association for Automotive Medicine (Morton Grove, Ill.: AAAM, 1977), pp. 101-22.

improved reaction times: See, for example, J. Crosley and M. J. Allen, “Automobile Brake Light Effectiveness: An Evaluation of High Placement and Accelerator Switching,” American Journal of Optometry and Archives of American Academy of Optometry, vol. 43 (1966), pp. 299-304. For a good history of brake lights and the various issues involved, see D. W. Moore and K. Rumar, “Historical Development and Current Effectiveness of Rear Lighting Systems,” Report No. UMTRI-99-31, 1999, University of Michigan Transportation Research Institute, Ann Arbor.

cut by 50 percent: The trial is described in John Voevodsky, “Evaluation of a Deceleration Warning Light for Reducing Rear-End Automobile Collisions,” Journal of Applied Psychology, vol. 59 (1974), pp. 270-73.

to around 15 percent: Charles Farmer, “Effectiveness Estimates for Center High Mounted Stop Lamps: A Six-Year Study,” Accident Analysis & Prevention, vol. 28, no. 2 (1996), pp. 201-08.

crashes by 4.3 percent: See Suzanne E. Lee, Walter W. Wierwille, and Sheila G. Klauer, “Enhanced Rear Lighting and Signaling Systems: Literature Review and Analyses of Alternative System Concepts,” DOT HS 809 425, National Highway Traffic Safety Administration, March 2002.

inventors had hoped: Critics of the chimsil have attributed its underwhelming impact in part to the idea that drivers do not necessarily brake when they see brake lights illuminated. The chimsil, this critique goes, offers more information, but more of the same information. It says nothing, for example, about how quickly a car is decelerating or whether it has, in fact, stopped—a key consideration given the majority of rear-end collisions involving stopped cars. The work of R. G. Mortimer has provided the most thoroughgoing critique of the chimsil. See, for example, R. G. Mortimer, “The High-Mounted Brake Light: The 4% Solution,” Society of Automotive Engineers Technical Paper 1999-01-0089, 1999.

by someone else: L. Evans and P. Gerrish, “Anti-lock Brakes and Risk of Front and Rear Impact in Two-Vehicle Crashes,” Accident Analysis & Prevention, vol. 28 (1996), pp. 315-23.

non-ABS drivers did: Elizabeth Mazzae, Frank S. Barickman, and Garrick J. Forkenbrock, “Driver Crash Avoidance Behavior with ABS in an Intersection Incursion Scenario on Dry Versus Wet Pavement,” Society of Automotive Engineers Technical Paper, 1999-01-1288, 1999.

braking the wrong way: A. F. Williams. and J. K. Wells, “Driver Experience with Antilock Brake Systems,” Accident Analysis & Prevention, vol. 26 (1994), pp. 807-11.

“close to zero”: Charles J. Kahane, “Preliminary Evaluation of the Effectiveness of Antilock Brake Systems for Passenger Cars,” NHTSA Report No. DOT HS 808 206, December 1994.

“has never been explained”): Insurance Institute for Highway Safety, Status Report, vol. 35, no. 4 (April 15, 2000).

guide, it will not: Nick Bunkley, “Electronic Stability Control Could Cut Fatal Highway Crashes by 10,000,” New York Times, April 6, 2007. One key difference to note with ESC versus ABS is that ESC functions on its own—it does not need to be used “correctly,” as in the case of ABS.

railroad safety improvements: Charles Francis Adams, in his 1879 book Notes on Railroad Accidents, wrote: “It is a favorite argument with those who oppose the introduction of some of these improvements, or who make excuses for want of them, that their servants are apt to become more careless from the use of them, in consequence of the extra security which they are believed to afford; and it is desirable to consider how much truth there is in this assertion.” As it happens, Adams did not subscribe to this early offset hypothesis: “The risk is proved by experience to be very much greater without them than with them; and, in fact, the negligence and mistakes of servants are found to occur most frequently, and generally with the most serious results, not when the men are over-confident in their appliances or apparatus, but when, in the absence of them, they are habituated to risk in the conduct of the traffic.” Interestingly, though, in a passage that still applies today, he noted that accidents at grade crossings, then as now, seemed to happen under what would be presumed to be the least likely, or “safest,” of conditions: “The full average of accidents of the worst description appear to have occurred under the most ordinary conditions of weather, and usually in the most unanticipated way. This is peculiarly true of accidents at highway grade crossings. These commonly occur when the conditions are such as to cause the highway travelers to suppose that, if any danger existed, they could not but be aware of it.” From Charles Francis Adams, Notes on Railroad Accidents (New York: G. P. Putnam’s Sons, 1879).

“the highway death rate”: Sam Peltzman, “The Effects of Automobile Safety Regulation,” Journal of Political Economy, vol. 83, no. 4 (August 1976), pp. 677-726.

reason to feel less safe: Decades later, people are still sifting through the data, trying to refute or defend Peltzman’s hypothesis. He has been questioned for, among other things, including motorcyclists in his count of nonoccupant fatalities—that is, along with pedestrians and cyclists—as if they were a similar beast. (Annual motorcycle registrations were also growing, it has been argued, and many motorcyclists, in any case, die in single-vehicle crashes, which are presumably not the result of car drivers acting more aggressively.) See, for example, Leon S. Robertson, “A Critical Analysis of Peltzman’s ‘The Effects of Automobile Safety Regulation,’” Journal of Economic Issues,vol. 2, no. 3 (September 1977), pp. 587-600. Others have suggested that people may not have been driving more aggressively but simply more—driving more in the newer cars because they felt safer (arguably a form of behavioral adaptation itself). See Robert B. Noland, “Traffic Fatalities and Injuries: Are Reductions the Result of ‘Improvements’ in Highway Design Standards?,” paper submitted to Annual Meeting of the Transportation Research Board, November 10, 2000. A study by a pair of Harvard economists that paid specific attention to how many people were actually using seat belts (again, something that can only be guessed at) found no evidence for a Peltzman effect. The authors did, however, conclude that fatalities had not dropped by nearly as much as government regulators had predicted. See Alma Cohen and Liran Einav, “The Effects of Mandatory Seat Belt Laws on Driving Behavior and Traffic Fatalities,” Discussion Paper No. 341, Harvard Law School, November 2001; downloaded on February 12, 2007, from Peltzman was also criticized for not separating, or “disaggregating,” the regulated vehicles from the nonregulated vehicles (to see, for example, if the cars with safety upgrades were overrepresented in fatal pedestrian crashes). This argument was made by Leon Robertson and Barry Pless, “Does Risk Homeostasis Theory Have Implications for Road Safety,” British Medical Journal, vol. 324 (May 11, 2002), pp. 1151-52.

to be riskier drivers: This point is made explicit in the discussion of the fictional Fred earlier in the chapter, but see, too, P. A. Koushki, S. Y. Ali, and O. AlSaleh, “Road Traffic Violations and Seat Belt Use in Kuwait: Study of Driver Behavior in Motion,” Transportation Research Record, vol. 1640 (1998), pp. 17-22; see also T. B. Dinh-Zarr, D. A. Sleet, R. A. Shults, S. Zaza, R. W. Elder, J. L. Nichols, R. S. Thompson, and D. M. Sosin, “Reviews of Evidence Regarding Interventions to Increase the Use of Safety Belts,” American Journal of Preventive Medicine, vol. 21, no. 4, Supp. 1 (2001), pp. 48-65, and D. F. Preusser, A. F. Williams, and A. K. Lund, “The Effect of New York’s Seat Belt Use Law on Teenage Drivers,” Accident Analysis & Prevention, vol. 19 (1987), pp. 73-80.

not wearing their belts: Evans, Traffic Safety, op. cit., p. 89.

“frequently get into accidents”: Russell S. Sobel and Todd M. Nesbit, “Automobile Safety Regulation and the Incentive to Drive Recklessly: Evidence from NASCAR,” Southern Economic Journal, vol. 74, no. 1 (2007).

suits and helmets: This point is made by Stephen J. Dubner and Steven D. Levitt in “How Many Lives Did Dale Earnhardt Save?” New York Times, February 19, 2006. They note that if NASCAR drivers had died at the same rate as American drivers in general in a five-year period, fifteen drivers should have died—instead, none did. This raises the interesting point that Earnhardt’s death became something of a spur for greater safety on NASCAR racetracks, where no single death in the general population of drivers seems capable of prompting a similar response.

fatalities by some 25 percent: A. J. McLean, B. N. Fildes, C. J. Kloeden, K. H. Digges, R. W. G. Anderson, V. M. Moore, and D. A. Simpson, “Prevention of Head Injuries to Car Occupants: An Investigation of Interior Padding Options,” Federal Office of Road Safety, Report CR 160, NHMRC Road Accident Research Unit, University of Adelaide and Monash University Accident Research Centre.

seat belts and air bags: Sam Peltzman, “Regulation and the Natural Progress of Opulence,” lecture presented at the American Enterprise Institute, September 8, 2004, AEI-Brookings Joint Center for Regulatory Studies, Washington, D.C.

Simpson has suggested: Joe Simpson, writing about “super-share ice screws” and other technological innovations, notes that “one would have thought these welcome developments would have made the sport considerably safer. Unfortunately climbers now throw themselves onto ice climbs that would have been unheard-of only a decade ago.” He then draws a comparison to his car, a “rust bucket of a Mini” that “left you with no illusions as to what a small cube of twisted metal it could instantly become if you hit anything.” As a result, he writes, “I drove with a modicum of caution.” From The Beckoning Silence (Seattle: Mountaineers Books, 2006), p. 105.

for more “safety”: The Mount McKinley information comes from a fascinating study by R. Clark and Dwight R. Lee, “Too Safe to Be Safe: Some Implications of Short- and Long-Run Rescue Laffer Curves,” Eastern Economic Journal, vol. 23, no. 2 (Spring 1997), pp. 127-37. It is true that many more people were climbing the mountain by the century’s end, but it is also true that many more climbers were needing to be rescued. In 1976 alone, the study notes, there were thirty-three rescues, one out of every eighteen climbs—almost as many as the total number prior to 1970.

no-pull fatality: Vic Napier, Donald Self, and Carolyn Findlay, “Risk Homeostasis: A Case Study of the Adoption of a Safety Innovation on the Level of Perceived Risk,” paper submitted to the American Society of Business and Behavioral Sciences meeting, Las Vegas, February 22, 2007.

our willingness for risk: O. Adebisi and G. N. Sama, “Influence of Stopped Delay on Driver Gap Acceptance Behavior,” Journal of Transportation Engineering, vol. 3, no. 115 (1989), pp. 305-15.

fatal crashes goes down: Daniel Eisenberg and Kenneth E. Warner, “Effects of Snowfalls on Motor Vehicle Collisions, Injuries, and Fatalities,” American Journal of Public Health, vol. 95, no. 1 (January 2005), pp. 120-24.

perfect risk “temperature”: Robertson and Pless, “Does Risk Homeostasis Theory Have Implications for Road Safety,” op. cit.

the lookout for cars: For a Palo Alto report, see Alan Wachtel and Diana Lewiston, “Risk Factors for Bicycle-Motor Vehicle Collisions at Intersections,” ITE Journal, September 1994. See also L. Aultmann-Hall and M. F. Adams. “Sidewalk Bicycling Safety Issues,” Transportation Research Record, no. 1636, 1998, pp. 71-76. For a fascinating and in-depth discussion of bicycle risk and safety issues, see Jeffrey A. Hiles, “Listening to Bike Lanes,” September 1996; retrieved on November 14, 2006, at

than those without them): See, for example, Lasse Fridstrom, “The Safety Effect of Studded Tyres in Norwegian Cities,” Nordic Road and Transport Research, no. 1 (2001), as well as Veli-Pekka Kallberg, H. Kanner, T. Makinen, and M. Roine, “Estimation of Effects of Reduced Salting and Decreased Use of Studded Tires on Road Accidents in Winter,” Transportation Research Record, vol. 1533 (1995).

drivers of larger cars: Paul Wasielewski and Leonard Evans, “Do Drivers of Small Cars Take Less Risk in Everyday Driving?,” Risk Analysis, vol. 5, no. 1 (1985), pp. 25-32.

higher speeds and more lanes: D. Walton and J. A. Thomas, “Naturalistic Observations of Driver Hand Positions,” Transportation Research Part F: Traffic Psychology and Behavior, vol. 8 (2005), pp. 229-38.

lower feelings of risk: D. Walton and A. Thomas, “Measuring Perceived Risk: Self-reported and Actual Hand Positions of SUV and Car Drivers,” Transportation Research Part F: Traffic Psychology and Behaviour, vol. 10, issue 3 (May 2007).

talking on a cell phone: Lesley Walker, Jonathan Williams, and Konrad Jamrozik, “Unsafe Driving Behaviour and Four Wheel Drive Vehicles: Observational Study,” British Medical Journal, vol. 333, issue 17558 (July 8, 2006), p. 71.

“car in front”: Sten Fossser and Peter Christensen, “Car Age and the Risk of Accidents,” TOI Report 386, Institute of Transport Economics, Norway, 1998.

more than old cars: This was suggested to me in a conversation with Kim Hazelbaker, senior vice president of the Insurance Institute for Highway Safety, May 19, 2007.

drive it more often: When I asked Leonard Evans, one of the leading authorities on traffic safety in the United States, what kind of car he drove, his answer made an impression on me. “In terms of a certain mind-set I drive a very unsafe car,” he said. “It’s about the least expensive, lightest car that my former employer manufactured: the Pontiac Sunfire.” It is well over a decade old.

and killed in war: Shaoni Bhattacharya, “Global Suicide Toll Exceeds War and Murder,” New Scientist, September 8, 2004.

struck by lightning: John Mueller, “A False Sense of Insecurity,” Regulation, vol. 27, no. 3 (Fall 2004), pp. 42-46.

stricter cell phone laws): Frank McKenna, a professor of psychology at the University of Reading, points out that people have commonly resisted previous traffic and other health safety measures, ranging from wearing seat belts to restricting workplace smoking, on the grounds that they impinge upon “freedoms.” There is also, in public policy, a tendency to avoid legislating behaviors that do not violate John Stuart Mill’s “harm principle”—that is, this thinking maintains that laws should be passed only to “prevent harm to others,” not for the “physical or moral” good of any individual. As McKenna argues, even though drunk driving and not wearing seat belts were once considered legitimate behavior, the social costs of these behaviors, as with workplace smoking, were eventually recognized. This raises the question, however, of why speeding, which can cause “harm to others,” is so widely tolerated. It may be that, as has been argued in this book, people are often simply not aware of their speed, or of the potential risks they are assuming in driving at a high speed. This may help contribute to a perceived lack of “legitimacy” on the part of authorities in trying to mount stricter enforcement campaigns. Police are faced with a well-known quandary: Be too lenient in enforcing strict speed limits, and drivers’ speeds will creep up; be too strict, and “they risk strain on public acceptability.” McKenna concludes that the current public acceptance of regularly driving above speed limits may at some point look as retrograde as workplace smoking: “It is noted that the perceived legitimacy of action can change considerably over time and interventions that would not be perceived as legitimate at one point in time may be considered uncontroversial at a later point in time.” See Frank P. McKenna, “The Perceived Legitimacy of Intervention: A Key Feature for Road Safety,” AAA Foundation for Traffic Safety, 2007.

drive rather than fly: “Consequences for Road Traffic Fatalities of the Reduction in Flying Following September 11, 2001,” Michael Sivak and Michael Flannagan, Transportation Research Part F: Traffic Psychology and Behavior,vol. 7, nos. 4-5 (July-September 2004), pp. 301-05.

assigned to counterterrorism: Carl Ingram, “CHP May Get to Hire 270 Officers,” Los Angeles Times, June 2, 2004, p. B1. In the article, one police officer points out that Timothy McVeigh was caught on a “routine traffic stop.” Eerily enough, Mohammed Atta, the ringleader of the September 11 participants, was ticketed once for speeding and once for driving without a license; the license he finally got was suspended when he failed to appear in court.

raising speed limits: Elihu D. Richter, Lee S. Friedman, Tamar Berman, and Avraham Rivkind, “Death and Injury from Motor Vehicle Crashes: A Tale of Two Countries,” American Journal of Preventative Medicine, vol. 29, no. 5 (2005), pp. 440-50. The authors implicate several other differences, including the steep rise in ownership of SUVs and other light trucks in the United States in the 1990s, as well as higher rates of driving under the influence of alcohol.

would have been killed: This point was raised in a letter by Leonard Evans in response to the previous article. American Journal of Preventative Medicine, vol. 30, no. 6 (2006), p. 532.

“psychophysical numbing”: D. Fetherstonhaugh, P. Slovic, S. Johnson, and J. Friedrich, “Insensitivity to the Value of Human Life: A Study of Psychophysical Numbing,” Journal of Risk and Uncertainty, vol. 14, no. 3 (1997), pp. 282-300.

of a terrible disease: Karen E. Jenni and George Lowenstein, “Explaining the ‘Identifiable Victim Effect,’” Journal of Risk Uncertainty, vol. 14 (1997), pp. 235-37.

only one more child: Paul Slovic, “If I Look at the Mass I Will Never Act: Psychic Numbing and Genocide,” Judgement and Decision Making, vol. 2, no. 2 (April 2007), pp. 1-17.

all who died: One exception to this is found at, which has tracked fatalities and crashes in the New York metropolitan area.

“dread” and “novelty”: B. Fischhoff, P. Slovic, S. Lichtenstein, S. Read, and B. Combs, “How Safe Is Safe Enough? A Psychometric Study of Attitudes Towards Technological Risks and Benefits,” Policy Sciences, vol. 9 (1978), pp. 127-52.

(like nuclear power): In New York City, an undercurrent of public opinion says that bicycles are “dangerous.” Neighborhoods have fought against the addition of bike lanes for this very reason. Yet one could count the number of people killed by bicycles in New York City each year on one hand, with a few fingers left over, while many times that number of people are killed or severely injured by cars. When I met with Ryan Russo, an engineer with the New York City Department of Transportation, I could not help but hear the echo of several of the reasons why we misperceive risk. “It’s silent and it’s rare,” he told me, when I asked about New Yorkers’ antipathy toward cyclists. “As opposed to cars, which make noise and are prevalent. You don’t see it because it’s smaller, you don’t hear it approach because it’s silent, and you don’t expect it because it’s not prevalent.” A close call with a cyclist, no matter how less dangerous statistically, stands out as the greater risk than a close call with a car, even though—or in fact precisely because—pedestrians are constantly having near-hazardous encounters with turning cars in crosswalks.

seem to be misperceived: A classic case, pointed out by Leonard Evans, is the specter of “vehicle recalls.” Every month or so, the news announces that some particular model of car has a potential defect. These recalls haunt us, raising our hackles with a constant stream of exploding tires and potentially faulty brakes. The cumulative result of this, Evans suggested, is that we may come to feel that the greatest threat to a driver’s safety is the improper functioning of his or her vehicle. “They will say on the news there are ‘no injuries reported,’” Evans said. We may feel relieved; the system works. “But the previous night there might have been a thousand people injured in crashes. And we’re told it’s the recall that is important.”

those killed by lightning): An analysis by AAA found 10,037 incidents of “violent and aggressive driving” between January 1, 1990, and August 31, 1996, that led to the deaths of 218 people. An estimated 37 percent of those cases involved a firearm. Cited by David K. Willis of AAA in Road Rage: Causes and Dangers of Aggressive Driving; Hearings Before the Subcommittee on Surface Interpretation of the House Committee on Transportation and Infrastructure, 105th Congress, 1st Session, 1997. As Michael Fumento has pointed out, in the same time span that these 218 “aggressive driving” deaths were registered, some 290,000 people were killed on the road. See Fumento, “‘Road Rage’ vs. Reality,” Atlantic Monthly, August 1998.

than pistol-packing drivers: Traces of the sleeping pill Ambien, not taken as prescribed, have been showing up in the bloodstreams of drivers involved in crashes. See Stephanie Saul, “Some Sleeping Pill Users Range Far Beyond Bed,” New York Times, March 8, 2006. But many other drugs of the kind that typically warn users not to “operate heavy machinery” while taking them also show up in the bodies of drivers (who apparently forget that cars are heavy machinery); for example, dextromethorphan, a synthetic analogue of codeine that appears frequently in over-the-counter medicines. See Amy Cochems, Patrick Harding, and Laura Liddicoat, “Dextromethorphan in Wisconsin Drivers,” Journal of Analytical Toxicology, vol. 31, no. 4 (May 2007), pp. 227-32.

if they pick the numbers: This phenomenon was described by psychologist Ellen Langer, who called it the “illusion of control.” See E. J. Langer, “The Illusion of Control,” Journal of Personality and Social Psychology, vol. 32, no. 2 (1975), pp. 311-28.

real dangers cars present: Consider, for example, the fact that, in the United States at least, hardly any children walk to school anymore—the figure has dropped from 48 percent in 1969 to under 15 percent in 2001. One perceived reason is “stranger danger.” But abductions, by strangers or family members, the U.S. Department of Justice has noted, make up only 2 percent of violent crimes against juveniles. Riding in the family car, and not “stranger danger,” is the greatest risk to people aged four to thirty-seven in the United States (and many other places). The car is actually a risk before it even leaves the driveway. In 2007, more than two hundred children were killed in the United States in “nontraffic fatalities,” a grim category that includes everything from “backover” incidents (typically in “safe” SUVs) to the hyperthermia of children unintentionally left in cars. For abduction statistics, see D. Finklehor and R. Ormrod, “Kidnapping of Juveniles: Patterns from NIBRS,” Juvenile Justice Bulletin, June 2000. Children’s walk-to-school rates come from Reid Ewing, Christopher V. Forinash, and William Schroeer, “Neighborhood Schools and Sidewalk Connections: What Are the Impacts on Travel Mode Choice and Vehicle Emissions?,” TR News, vol. 237 (March-April 2005). School bus fatality risks are taken from Ann M. Dellinger and Laurie Beck, “How Risky Is the Commute to School,” TR News, vol. 237 (March-April 2005).

more dangerous it is: This information comes from a study by William Lucy, a University of Virginia professor of urban planning. His findings are based on two key mortality indices: chance of being killed by a stranger and risk of being killed in traffic. See Lucy, “Mortality Risk Associated with Leaving Home: Recognizing the Relevance of the Built Environment,” American Journal of Public Health, vol. 93, no. 9 (September 2003), pp. 1564-69.

(roughly 22 miles per hour): In 2006, there were 14 traffic fatalities recorded in Bermuda, though that number was set to rise to 20 in 2007. See Tim Smith, “Call for Greater Police Presence to Tackle Road Deaths ‘Epidemic,’” Royal Gazette, November 24, 2007. This is actually quite a high number for a country with a population of some 66,000 (not including the many tourists who visit). Typically, however, 80 percent of these fatalities involve the riders or passengers of motorbikes, and a high percentage of those involve tourists who are either unfamiliar with the roads (or the bikes) or presumably have been drinking. Tourists in Bermuda are estimated to be almost six times at risk for being injured on a motorbike than are local residents. See M. Carey, M. Aitken, “Motorbike Injuries in Bermuda: A Risk for Tourists,” Annals of Emergency Medicine, vol. 28, Issue 4, pp. 424-29. Other studies have shown tourists to be overrepresented in car crashes. See C. Sanford, “Urban Medicine: Threats to Health of Travelers to Developing World Cities,” Journal of Travel Medicine, vol. 11, no. 5 (2004), pp. 313-27. John Adams brought up the Bermuda example in his book Risk and Freedom: The Record of Road Safety (Cardiff: Transport Publishing Projects, 1985), p. 2. He quotes, in turn, Herman Kahn, The Next 200 Years (New York: William Morrow, 1976), p. 168.

cars and cyclists: Based on a conversation with city manager Judie Zimomra and police department records specialist Bob Conklin. Zimomra noted that there were traffic fatalities in the 1990s, but subsequent enforcement and engineering efforts have proven successful. The lesson: Speed is important, but hardly the only issue.

lowers crash risks: C. N. Kloeden, A. J. McClean, and G. Glonek, “Reanalysis of Travelling Speed and Risk of Crash Involvement in Adelaide, South Australia,” Australian Transport Safety Bureau Report CR 207, April 2002.

Adams calls “hypermobility”: See John Adams, “Hypermobility: Too Much of a Good Thing?,” Royal Society for the Arts Lecture, November 21, 2001. Retrieved at

roughly half the crashes: See Cherian Varghese and Umesh Shankar, “Restraint Use Patterns Among Fatally Injured Passenger Vehicle Occupants,” DOT HS 810 595, National Highway Traffic Safety Administration, May 2006.

slow level of 35 miles per hour: From a report prepared by Michael Paine, based on data taken from the U.S. National Highway Traffic Safety Administration from 1993 to 1997; retrieved from

(among other things): An observational study of a random sample of drivers in New York City found that those talking on a hands-free device were more likely to engage in other distracting activities (e.g., smoking, eating, grooming) than those speaking on a handheld cell phone. As the researchers observed, the drivers “may be trading one automobile-related risk for another.” See “Driving Distractions in New York City,” Hunter College, November 2007.

Epilogue: Driving Lessons

to pass the front: For an excellent discussion of the physics of oversteering and understeering, as well as driving in general, see Barry Parker, The Isaac Newton School of Driving: Physics and Your Car (Baltimore: Johns Hopkins University Press, 2003).

to maintain our course?: W. O. Readinger, A. Chatziastros, D. W. Cunningham, J. E. Cutting, and H. H. Bülthoff, “Gaze-Direction Effects on Drivers’ Abilities to Steer a Straight Course,” TWK Beiträge zur 4. Tübinger Wahrnehmungskonferenz, ed. H. H. Bülthoff, K. R. Gegenfurtner, H. A. Mallot, R. Ulrich. Knirsch, Kirchentellinsfurt, 149 (2001). Available at

“doing so at all”: See W. O. Readinger, A. Chatziastros, D. W. Cunningham, H. H. Bülthoff, and J. E. Cutting, “Gaze-Eccentricity Effects on Road Position and Steering,” Journal of Experimental Psychology: Applied, vol. 8, no. 4 (2002), pp. 247-58.

“might be your English teacher”: Actually, the traditional model of high school driver’s ed—usually classroom instruction plus on-road time—has been largely discredited. The reasons have less to do with the worth or validity of learning the rules of the road than with the fact that such programs, rather than helping to produce safer drivers, just seem to put more unsafe drivers on the road at a younger age. A number of studies have come to this conclusion, but see, in particular, J. Vernick, G. Li, S. Ogaitis, E. MacKenzie, S. Baker, and A. Gielen, “Effects of High School Driver Education on Motor Vehicle Crashes, Violations, and Licensure,” American Journal of Preventive Medicine, vol. 16, no. 1 (1999), pp. 40-46; M. F. Smith, “Research Agenda for an Improved Novice Driver Education Program: Report to Congress, May 31, 1994,” DOT HS 808 161, National Highway Traffic Safety Administration, retrieved from; and I. Roberts and L. Kwan, “School Based Driver Education for the Prevention of Traffic Crashes,” Cochrane Database of Systematic Reviews, no. 2 (2006).

skills needed to drive: Thanks to Leonard Evans for this reference.

stock-car drivers: A. F. Williams and B. O’Neill, “On-the-Road Driving Records of Licensed Race Drivers,” Accident Analysis & Prevention, vol. 6 (1974), pp. 263-70.

“not going fast enough”: Thanks to Leonard Evans for Andretti Quote.

to go next: Vision researchers studied the eye and head movements of Formula 3 racer Tomas Scheckter as he drove on the Mallory Park circuit in Leceistershire, England. They suggested that Scheckter, because he had learned the layout of the track, actually moved his head in the direction in which he wanted to go before he adjusted his steering. See Michael F. Land and Benjamin W. Tatler, “Steering with the Head: The Visual Strategy of a Racing Driver,” Current Biology, vol. 11 (2001), pp. 1215-20.

to avoid a crash: For an excellent summary of the research, see Lisa D. Adams, “Review of the Literature on Obstacle Avoidance Maneuvers: Braking Versus steering,” Report No. UMTRI-94-19, University of Michigan Transportation Research Institute, Ann Arbor, August 1994.

the only thing to do: Jeffrey Muttart raises the idea of “operant conditioning” in “Factors That Influence Drivers’ Response Choice Decisions in Video Recorded Crashes,” Society of Automotive Engineers Journal, 2005.

to their full power: See Rodger J. Koppa and Gordon G. Hayes, “Driver Inputs During Emergency or Extreme Vehicle Maneuvers,” Human Factors, vol. 18, no. 4 (1976), pp. 361-70.

the obstacle is moving: D. Fleury, F. Fernandez, C. Lepesant, and D. Lechner, “Analyse typologique des manoeuvres d’urgence en intersection,” Rapport de recherche INRETS, no. 62 (1988), quoted in Lisa D. Adams, 1994.

to the point where we do nothing: Michael A. Dilich, Dror Kopernik, and John M. Goebelbecker, “Evaluating Driver Response to a Sudden Emergency: Issues of Expectancy, Emotional Arousal, and Uncertainty,” Safety Brief, vol. 20, no. 4 (June 2002). A frequent occurrence in driving simulator studies that seek to evaluate how drivers respond to unexpected obstacles or hazards is that a small number of subjects often have “no response.” A French study, for example, in which drivers on a test track had to react to an inflatable “dummy car,” found that 4 percent of subjects did nothing, simply “freezing.” See Christian Collett, Claire Petit, Alain Priez, and Andre Dittmar, “Stroop Color-Word Test, Arousal, Electrodermal Activity and Performance in a Critical Driving Situation,” Biological Psychology, vol. 69 (2005), pp. 195-203.

car was going to do: D. Lechner and G. Maleterre, “Emergency Maneuver Experimentation Using a Driving Simulator,” Society of Automotive Engineers Technical Paper No. 910016, 1991; referenced in Dilich, Kopernik and Goebelbecker, op. cit.

“living room on wheels”: Micheline Maynard, “At Chrysler, Home Depot Still Lingers,” New York Times, October 30, 2007.

warnings he or she might disregard: See, for example, M. P. Manser, N. J. Ward, N. Kuge, and E. R. Boer, “Influence of a Driver Support System on Situation Awareness and Information Processing in Response to Lead Vehicle Braking,” Proceedings of the Human Factors and Ergonomics Society Forty-eighth Annual Meeting (New Orleans, Human Factors and Ergonomics Society, 2004), pp. 2359-63, and “Crash Warning System Interfaces,” DOT HS 810 697, January 2007.

be able to react accordingly: This is one of the problems that plague automation. Barry Kantowitz at the University of Michigan notes that automation “works fine up to a certain point, and then it fails utterly and completely.” He uses the example of a plane crash in which the autopilot, in attempting to correct for an imbalance in fuel, tipped the plane to the point where the autopilot couldn’t control it any longer. “So essentially it did the equivalent of ringing a bell and telling the pilot, ‘Okay, you take over now,’” he says. “You have a pilot who’s unaware there’s a problem. He’s ‘out of the loop.’ He has to very quickly figure out what the hell happened.” But when people fail, they have what he calls a “graceful degradation. They fail slowly instead of abruptly. They can cope with it a little better.” Design theorist Donald Norman gives a driving example in his book The Design of Future Things: A friend was driving with adaptive cruise control. This is the device that measures the distance away in time, in speed, of the vehicle in front, and keeps the car automatically at a safe distance. But, Norman notes, his friend suddenly moved to exit the freeway, forgetting the ACC was on. The car, thinking it suddenly had clear road ahead, chose to accelerate at the very moment it should have been decelerating. Automation is supposed to relieve the driver of having to pay attention, but in this case, if the driver hadn’t been paying attention there would have likely been a severe crash. Norman argues that while full automation would be safer than human manual driving, the “difficulty lies in the transition towards full automation, when different vehicles will have different capabilities, when only some things will be automated, and when even the automation that is installed will be limited in capability.” See Donald Norman, The Design of Future Things (New York: Basic Books, 2007), p. 116.

memory playing tricks): A group of psychologists at the University of Nottingham showed subjects a series of eight-second film clips of “dangerous” and “safer” situations that had been digitally manipulated to play at a range of faster or slower speeds (but always for eight seconds). Subjects were more likely to have judged the “dangerous” films as having been sped up. “If real dangerous events are remembered as if time slowed down,” the authors write, “this will create an expectation that videos of such events should run slowly…. Becausethe actual speed of the video does not slow down, viewers will judge films of dangerous events as having been sped up.” See Peter Chapman, Georgina Cox, and Clara Kirwan, “Distortion of Drivers’ Speed and Time Estimates in Dangerous Situations,” in Behavioral Research in Road Safety (London: Transport for London, 2005), pp. 164-74.