Traffic (49 page)

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

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
http://www.sci.csuhayward.edu/~jkwon/
, 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.