Traffic_ Why We Drive The Way We Do Part 13

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, Proceedings of the Royal Society: Biological Science, v. 270 (1511), January 22, 2003, pp. 13946. v. 270 (1511), January 22, 2003, pp. 13946.

"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, National Geographic, July 2007. July 2007.

ongoing labor dispute: Sharon Bernstein and Andrew Blankstein, "2 Deny Hacking Into L.A.'s Traffic Light System," Los Angeles Times, Los Angeles Times, January 9, 2007. 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 Emergence (New York: Scribner, 2001), p. 96. (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, Los Angeles Times, October 17, 2007. 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, a.n.a.lytical, and Field Observations," Transportation Research Record, Transportation Research Record, No. 76, Annual Meeting of the Transportation Research Board, Was.h.i.+ngton, D.C., 1997, pp. 5663. No. 76, Annual Meeting of the Transportation Research Board, Was.h.i.+ngton, D.C., 1997, pp. 5663.

to help move the fewer cars: The city of Amsterdam, for example, has inst.i.tuted 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 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, 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 City (New York: Doubleday, 1988), p. 61. (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, Transportation Research Part F: Traffic Psychology and Behaviour, vol. 7, no. 6 (November 2004), pp. 395404. 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," vol. 7, no. 6 (November 2004), pp. 395404. 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, Behavioral Sciences and the Law, vol. 19 (2001), pp. 26583. vol. 19 (2001), pp. 26583.

"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 a.n.a.lysis & Prevention, Accident a.n.a.lysis & Prevention, vol. 36 (2004), pp. 63747. vol. 36 (2004), pp. 63747.

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 a.s.sociate with vehicular traffic all sorts of phantom phenomena a.n.a.logous 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 a.n.a.lyzed only by crude approximations." G. F. Newell, "Memoirs on Highway Traffic Flow Theory in the 1950s," Operations Research, Operations Research, vol. 50, no. 1 (JanuaryFebruary 2002), pp. 17378. vol. 50, no. 1 (JanuaryFebruary 2002), pp. 17378.

"puzzles remain unsolved": See Carlos Daganzo, "A Behavioral Theory of Multi-lane Traffic Flow, Part I: Long h.o.m.ogeneous Freeway Sections," Transportation Research Part B: Methodological, Transportation Research Part B: Methodological, vol. 36, no. 2 (February 2002), pp. 13158. vol. 36, no. 2 (February 2002), pp. 13158.

"heterogeneity of driver behavior": In his superb book Critical Ma.s.s, Critical Ma.s.s, 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, 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 Ma.s.s Critical Ma.s.s (New York: Farrar, Straus and Giroux, 2004), p. 160. (New York: Farrar, Straus and Giroux, 2004), p. 160.

when they followed pa.s.senger 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 Inst.i.tute, June 2000.

Los Gatos effect: Carlos F. Daganzo, "A Behavioral Theory of Multi-Lane Traffic Flow," Part I: Long h.o.m.ogeneous Freeway Sections." Transportation Research Part B: Methodological, vol. 36, no 2 (Febryary 2002), pp 13158.

traveling at 55 miles per hour: In 1985, the Highway Capacity Manual, 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, 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 2004 Status of the Nation's Highways, Bridges and Transit: Conditions and Performance (Was.h.i.+ngton, D.C.: 2004), U.S. Department of Transportation, pp. 416. 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. (Was.h.i.+ngton, D.C.: 2004), U.S. Department of Transportation, pp. 416. 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 pa.s.s 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. Ca.s.sidy, 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 enhanced the flow of traffic through troublesome bottlenecks. See J. Kwon and P. Varaiya, "Effectiveness of High-Occupancy Vehicle (HOV) Lanes in the San Francis...o...b..y Area," July 2006, available at the flow of traffic through troublesome bottlenecks. See J. Kwon and P. Varaiya, "Effectiveness of High-Occupancy Vehicle (HOV) Lanes in the San Francis...o...b..y Area," July 2006, available at http://www.sci.csuhayward.edu/~jkwon/, and Michael J. Ca.s.sidy, Carlos F. Daganzo, Kitae Jung, and Koohong Chung, "Empirical Rea.s.sessment 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. Ca.s.sidy, and R. L. Bertini, Department of Civil and Environmental Engineering and Inst.i.tute 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 Ca.s.sidy, "Complications at Off-Ramps," Access Access magazine, January 2003, pp. 2731. magazine, January 2003, pp. 2731.

one-third less time: The rice experiment (proposed by Paul Haase) was the winning entry in a contest sponsored by the Was.h.i.+ngton DOT for the best way to visualize "throughput maximization" Susan Gilmore, "Rice Is Nice When Trying to Visualize Highway Traffic," Seattle Times, Seattle Times, December 29, 2006. 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 compet.i.tion between driving forces and dissipative interactions leads to self-organized structures: Indeed, there is a strong a.n.a.logy between the formation of traffic jams on the highway and the formation of particle cl.u.s.ters 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, 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. 56978. On the other hand, G. F. Newell, a seminal traffic flow researcher, once cautioned that "some researchers try to a.s.sociate with vehicular traffic all sorts of phantom phenomena a.n.a.logous to the effects in gases. They don't exist." G. F. Newell, "Memoirs on Highway Traffic Flow Theory in the 1950s," eds. S. P. Hoogendoorn, S. Luding, P. H. L. Bovy, M. Schreckenberg, and D. E. Wolf (Berlin: Springer, 2005), pp. 56978. On the other hand, G. F. Newell, a seminal traffic flow researcher, once cautioned that "some researchers try to a.s.sociate with vehicular traffic all sorts of phantom phenomena a.n.a.logous to the effects in gases. They don't exist." G. F. Newell, "Memoirs on Highway Traffic Flow Theory in the 1950s," Operations Research, Operations Research, vol. 50, no. 1 (JanuaryFebruary 2002), pp. 17378. vol. 50, no. 1 (JanuaryFebruary 2002), pp. 17378.

"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, Reviews of Modern Physics, vol. 73, no. 4 (2001), pp. 10671141. vol. 73, no. 4 (2001), pp. 10671141.

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, California Department of Transportation Journal, vol. 2 (MayJune 2002), pp. 4247. vol. 2 (MayJune 2002), pp. 4247.

1,320 vehicles per hour: Robert Herman and Keith Gardels, "Vehicular Traffic Flow," Scientific American, Scientific American, vol. 209, no. 8 (December 1963). 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 pa.s.senger 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. k.o.c.kelman and Raheel A. Shabih, "Effect of Vehicle Type on the Capacity of Signalized Intersections: The Case of Light-Duty Trucks," Journal of Transportation Engineering, Journal of Transportation Engineering, vol. 126, no. 6 (1999), pp. 50612. vol. 126, no. 6 (1999), pp. 50612.

stop on red: See, for example, Matt Helms, "Wait Just Two Seconds Before You Start," Free Press, Free Press, June 18, 2007. 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, Was.h.i.+ngton, 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, Journal of Transportation Engineering, vol. 131, no. 6 (2005), pp. 397407. vol. 131, no. 6 (2005), pp. 397407.

wreak progressive havoc: See Philip Ball, "Slow, Slow, Quick, Quick, Slow," Nature, Nature, April 17, 2000. For the original research, see T. Nagatani, "Traffic Jams Induced by Fluctuation of a Leading Car," April 17, 2000. For the original research, see T. Nagatani, "Traffic Jams Induced by Fluctuation of a Leading Car," Physical Review E, Physical Review E, vol. 61 (2000), pp. 353440. vol. 61 (2000), pp. 353440.

effects of a shock wave: See P. Breton, A. Hegy, B. De Schutter, and H. h.e.l.lendoorn, "Shock Wave Elimination/Reduction by Optimal Coordination of Variable Speed Limits," Proceedings of the IEEE Fifth International Conference on Intelligent Transportation Proceedings of the IEEE Fifth International Conference on Intelligent Transportation Systems (ITSC '02), Singapore, pp. 22530, September 2002. Systems (ITSC '02), Singapore, pp. 22530, September 2002.

trip times declined: Highways Agency, M25 Controlled Motorways: Summary Report, M25 Controlled Motorways: Summary Report, November, 2004. 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 The Physics of Traffic: Empirical Freeway Pattern Features, Engineering Applications, and Theory (Berlin: Springer, 2004), p. 69. (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, Computational Science and Its Applications: ICCSA 2005, vol. 3481 (2005), pp. 86369. vol. 3481 (2005), pp. 86369.

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, ITS Berkeley Online Magazine, vol. 1, no. 2 (Winter 2005). 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 Inst.i.tute, Center for Transportation Studies, University of Minnesota, April 2006. 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 Inst.i.tute, 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, Physical Review E, vol. 69 (2004). 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, Scientific American, October 1997, pp. 5863. October 1997, pp. 5863.

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, Technological Forecasting and Social Change, vol. 47 (1994), pp. 7588. vol. 47 (1994), pp. 7588.

thirty minutes each way: M. Wachs, B. D. Taylor, N. Levine, and P. Ong, "The Changing Commute: A Case-study of the Jobs-Housing Relations.h.i.+p over Time," Urban Studies, Urban Studies, vol. 30, no. 10 (1993), pp. 171129. vol. 30, no. 10 (1993), pp. 171129.

jobs were located: See David Levinson and Ajay k.u.mar, "The Rational Locator," Journal of the American Planning a.s.sociation, Journal of the American Planning a.s.sociation, vol. 60, no. 3 (1994), pp. 31943. 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, Was.h.i.+ngton, D.C. vol. 60, no. 3 (1994), pp. 31943. 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, Was.h.i.+ngton, D.C.

jacking up the numbers: D. Levinson and Y. Wu, "The Rational Locator Reexamined," Transportation, Transportation, vol. 32 (2005), pp. 187202. vol. 32 (2005), pp. 187202.

prompts more driving: See Nancy McGuckin, Susan Liss, and Bryant Gross, "Do More Vehicles Make More Miles?" National Household Travel Survey National Household Travel Survey (Was.h.i.+ngton, D.C.: Federal Highway Administration, 2001). (Was.h.i.+ngton, 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, Access Magazine, no. 25 (Fall 2004). See also Scott F. Festin, no. 25 (Fall 2004). See also Scott F. Festin, Summary of National and Regional Travel Trends: 19701995 Summary of National and Regional Travel Trends: 19701995 (Was.h.i.+ngton, D.C.: U.S. Department of Transportation, Federal Highway Administration, 1996). (Was.h.i.+ngton, 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 Commuting in America III (Was.h.i.+ngton, D.C.: Transportation Research Board, 2006), p. 2. (Was.h.i.+ngton, 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, 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. 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, 19902000," Research on Women's Issues in Transportation, Report of a Conference, Vol. 2 Research on Women's Issues in Transportation, Report of a Conference, Vol. 2 (Was.h.i.+ngton, D.C.: Transportation Research Board, 2004). (Was.h.i.+ngton, 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, Was.h.i.+ngton, 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, Seattle Times, August 2, 2007. August 2, 2007.

more often than men do: See Research on Women's Issues in Transportation: Report of a Conference Research on Women's Issues in Transportation: Report of a Conference (Was.h.i.+ngton, D.C.: Transportation Research Board, National Research Council, 2005), p. 30. (Was.h.i.+ngton, 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, New York Times, September 11, 2007. September 11, 2007.

by some 30 percent: See U.S. Environmental Protection Agency, Travel and Environmental Implications of School Siting, 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, 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, Morning Peak Trip by Purpose, 1999. 1999.

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

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

typical rush hours: See Highway Statistics 2005 Highway Statistics 2005 (Was.h.i.+ngton, D.C.: Office of Highway Policy Information, Federal Highway Administration). (Was.h.i.+ngton, 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, Transportation, vol. 28, no. 4 (2001), pp. 31746. vol. 28, no. 4 (2001), pp. 31746.

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 Inst.i.tute for Transportation Engineers, "Trip Generation of Coffee Shops with Combination Drive-Through and Sit-Down Facilities" retrieved from http://www.cowyite.org/technical/.

left turn during rush hour: Starbucks also antic.i.p.ates 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 Starbucked (New York: Little, Brown, 2007). (New York: Little, Brown, 2007).

stalled queues of cars: Andrew Downie, "Postcard: Brazil," Time, 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." 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, Commuting in America III, p. 109. p. 109.

those without one: "Poverty and Mobility in America," NPTS Brief NPTS Brief (Was.h.i.+ngton, D.C.: U.S. Department of Transportation, Federal Highway Administration, December 2005). (Was.h.i.+ngton, 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 a.s.sociation, Journal of the American Planning a.s.sociation, vol. 72, no. 3 (Summer 2006), pp. 27984. vol. 72, no. 3 (Summer 2006), pp. 27984.

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, Science, vol. 306, no. 5702 (December 2004), pp. 177678. vol. 306, no. 5702 (December 2004), pp. 177678.

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 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. 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, Transportation Research Part A: Policy and Practice, vol. 39, nos. 23 (2005), pp. 183203. vol. 39, nos. 23 (2005), pp. 183203.

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: http://ssrn.com/abstract=408220.

grown the most: Robert H. Frank, Falling Behind Falling Behind (Berkeley: Univ. of California Press, 2007), p. 82. (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, Scientific Perspectives on Enjoyment, Suffering, and Well-Being, ed. D. Kahneman, E. Diener, and N. Schwartz (New York: Russell Sage Foundation, 1999), pp. 30329. ed. D. Kahneman, E. Diener, and N. Schwartz (New York: Russell Sage Foundation, 1999), pp. 30329.

more p.r.o.ne 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. Was.h.i.+ngton, 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, Journal of Transportation and Statistics, vol. 2, no. 2 (Dec. 1999), as well as David Brownstone and Kenneth A. Small, "Valuing Time and Reliability: a.s.sessing the Evidence from Road Pricing Demonstrations," vol. 2, no. 2 (Dec. 1999), as well as David Brownstone and Kenneth A. Small, "Valuing Time and Reliability: a.s.sessing the Evidence from Road Pricing Demonstrations," Transportation Research Part A: Policy and Practice, Transportation Research Part A: Policy and Practice, vol. 39, no. 4 (2005), pp. 27993. vol. 39, no. 4 (2005), pp. 27993.

"h.e.l.l every day": Jonathan Clements, "Money and Happiness? Here's Why You Won't Laugh," Wall Street Journal, Wall Street Journal, August 16, 2006. August 16, 2006.

higher rate than are pa.s.senger cars: T. Cohn, "On the Back of the Bus," Access, Access, vol. 21 (1999), pp. 1721. vol. 21 (1999), pp. 1721.

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 a.n.a.lysis & Prevention, Accident a.n.a.lysis & Prevention, vol. 26 (1994), pp. 18193; G. Evans, M. Palsane, and S. Carrere, "Type A Behavior and Occupational Stress: A Cross-cultural Study of Blue-Collar Workers," vol. 26 (1994), pp. 18193; 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, Journal of Personality and Social Psychology, vol. 52 (1987), pp. 100207; and Gary W. Evans and S. Carrere, "Traffic Congestion, Perceived Control, and Psychophysiological Stress Among Urban Bus Drivers," vol. 52 (1987), pp. 100207; and Gary W. Evans and S. Carrere, "Traffic Congestion, Perceived Control, and Psychophysiological Stress Among Urban Bus Drivers," Journal of Applied Psychology, Journal of Applied Psychology, vol. 76 (1991), pp. 65863. vol. 76 (1991), pp. 65863.

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, European Journal of Social Psychology, vol. 18, 1988, pp. 42942. vol. 18, 1988, pp. 42942.

"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, Science, vol. 312, no. 5782 (June 30, 2006), pp. 190810. vol. 312, no. 5782 (June 30, 2006), pp. 190810.

makes them think it is: We are also quite capable of changing the way we feel about something-or the way we think 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' att.i.tudes 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' att.i.tudes 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 att.i.tudes 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," 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' att.i.tudes 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' att.i.tudes 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 att.i.tudes 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, Social Psychology Quarterly, vol. 59 (1996), pp. 36474. vol. 59 (1996), pp. 36474.

less than 15 percent: Brian Taylor, "Rethinking Traffic Congestion," Access, Access, Fall 2002, pp. 8-16. 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 s.p.a.ces closest 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," 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, Chain Reaction, vol. 4 (2003), pp. 1819. 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," vol. 4 (2003), pp. 1819. 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, Journal of Arboriculture, vol. 25, no. 3 (May 1999), pp. 12941. vol. 25, no. 3 (May 1999), pp. 12941.

bell-curve arrangement: This idea was first suggested, as far as I can discern, at the following Web site: http://vandersluys.ca/?p=7914.

not necessarily being chosen: Velkey's findings matched those predicated by two engineering professors in a "probabilistic model." See C. Richard Ca.s.sady and John E. Kobza, "A Probabilistic Approach to Evaluate Strategies for Selecting a Parking s.p.a.ce," Transportation Science, Transportation Science, vol. 32, no. 1 (January 1998), pp. 3042. vol. 32, no. 1 (January 1998), pp. 3042.

to walk somewhere: Travel Behaviour Research Baseline Survey 2004: Sustainable Travel Demonstration Towns Travel Behaviour Research Baseline Survey 2004: Sustainable Travel Demonstration Towns (SUSTRANS and Socialdata, 2004). Retrieved from (SUSTRANS and Socialdata, 2004). Retrieved from http://www.sustrans.org.uk/webfiles/travelsmart/STDT%20Research%20FINAL.pdf.

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. 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, "s.e.x-Related Differences and Similarities in Geographic and Environmental Spatial Abilities," Annals of the a.s.sociation of American Geographers, Annals of the a.s.sociation of American Geographers, vol. 89 (1999), pp. 51534. vol. 89 (1999), pp. 51534.

as the distance did: A. J. Velkey, C. Laboda, S. Parada, M. L. McNeil, and R. Otts, "s.e.x Differences in the Estimation of Foot Travel Time," paper presented at the annual meeting of the Eastern Psychological a.s.sociation, 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 s.p.a.ce is. See Sigrid Schmitz, "Gender Differences in Acquisition of Environmental Knowledge Related to Wayfinding Behavior, Spatial Anxiety and Self-Estimated Environmental Competencies," s.e.x Roles: A Journal of Research, s.e.x Roles: A Journal of Research, July 1999. July 1999.

"optimal foraging": For a good introduction to optimal foraging, see T. Schoener, "A Brief History of Optimal Foraging Ecology," in Foraging Behavior, Foraging Behavior, ed. A. C. Kamil, J. R. Krebs, and H. R. Pulliam (New York: Plenum Press, 1987), pp. 567. See also Jeffrey A. Kurland and Stephen J. Beckerman, "Optimal Foraging and Hominid Evolution: Labor and Reciprocity," ed. A. C. Kamil, J. R. Krebs, and H. R. Pulliam (New York: Plenum Press, 1987), pp. 567. See also Jeffrey A. Kurland and Stephen J. Beckerman, "Optimal Foraging and Hominid Evolution: Labor and Reciprocity," American Anthropologist, American Anthropologist, vol. 87, no. 1 (March 1985), pp. 7393. vol. 87, no. 1 (March 1985), pp. 7393.

the effort of looking: This example is given in an interesting paper by Elizabeth Newell, a biologist at Hobart and William Smith Colleges, t.i.tled "The Energetics of Bee Foraging." Retrieved from http://www.life.umd.edu/Faculty/inouye/Pollination%20Exercises/Beth's.htm.