Traffic

by Tom Vanderbilt

  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 http://www.visualexpert.com/Resources/reactiontime.htm.

  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 Strate
gy 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; http://repositories.cdlib.org/its/tsc/UCB-TSC-TR-2007-10.

  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 http://www.psy.ucsd.edu/~sanstis/Foot.htm. 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 www.angel.elte.hu/wave/.

  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 Mil
ler, “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 http://www.nieuwsuitamsterdam.nl/English/2007/11/green_wave.htm.