is the better option: Esa Ranta, Hannu Rita, and Kai Lindstrom, "Compet.i.tion Versus Cooperation: Success of Individuals Foraging Alone and in Groups," American Naturalist, American Naturalist, vol. 142, no. 1 (July 1993), pp. 4258. vol. 142, no. 1 (July 1993), pp. 4258.

spot to a destination: Mark Schlueb, "To Get to Game or Show, Parking May Be Tricky," Orlando Sentinel, Orlando Sentinel, December 1, 2006. 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 Spatial Information Theory: A Theoretical Basis for GIS (Berlin: Springer, 1997), pp. 297311, and Lorin J. Staplin and Edward K. Sadalla, "Distance Cognition in Urban Environments," (Berlin: Springer, 1997), pp. 297311, and Lorin J. Staplin and Edward K. Sadalla, "Distance Cognition in Urban Environments," Professional Geographer, Professional Geographer, vol. 33 (1981), pp. 30210. vol. 33 (1981), pp. 30210.

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

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

subsidized parking spots: Bruce Schaller, "Free Parking, Congested Streets," March 1, 2007; available at http://www.schallerconsult.com/pub/index.htm.

"as has cycle parking s.p.a.ce": City of Copenhagen, Traffic and Environmental Plan 2004, Traffic and Environmental Plan 2004, p. 16. p. 16.

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

metered street spots: Donald C. Shoup, "Cruising for Parking," Transport Policy, Transport Policy, vol. 13 (2006), pp. 47986. vol. 13 (2006), pp. 47986.

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

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

all urban traffic collisions: See Paul C. Box, "Curb Parking Findings Revisited," Transportation Research Circular 501 Transportation Research Circular 501 (Washington, D.C.: Transportation Research Board, 2000). (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 20053147 Fact Sheet 20053147 (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." (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 s.p.a.ces Outnumber Drivers 3-to-1, Drive Pollution and Warming," Purdue University News Service, September 11, 2007. Douglas M. Main, "Parking s.p.a.ces 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 California's Global Gateway: Trends and Issues (San Francisco: Public Policy Inst.i.tute of California, 2004), p. 62. (San Francisco: Public Policy Inst.i.tute 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 pa.s.sengers 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 doc.u.mentary New York Underground New York Underground ( (American Experience).

like population growth: See Lewis M. Fulton, Robert B. Noland, Daniel J. Meszler, and John V. Thomas, "A Statistical a.n.a.lysis of Induced Travel Effects in the U.S. Mid-Atlantic Region," Journal of Transportation and Statistics, Journal of Transportation and Statistics, vol. 3, no. 1 (2000), pp. 114. 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," vol. 3, no. 1 (2000), pp. 114. 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, Transportation Research A, vol. 31 (1997), pp. 20518. Robert B. Noland, a scientist at Imperial College London, has compiled an extensive bibliography of "induced demand" research; it's available at vol. 31 (1997), pp. 20518. Robert B. Noland, a scientist at Imperial College London, has compiled an extensive bibliography of "induced demand" research; it's available at http://www.vtpi.org/induced_bib.htm.

on the affected roads: See S. Cairns, S. Atkins, and P. Goodwin, "Disappearing Traffic? The Story So Far," Munic.i.p.al Engineer, Munic.i.p.al Engineer, vol. 151, no. 1 (March 2002), pp. 1322. There was an interesting example of this phenomenon in New York City. When Christo's vol. 151, no. 1 (March 2002), pp. 1322. There was an interesting example of this phenomenon in New York City. When Christo's The Gates 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 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 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. 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 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. 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 why congestion is bad is quite fluid, often depending on the needs of a political cla.s.s. 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," congestion is bad is quite fluid, often depending on the needs of a political cla.s.s. 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, Journal of Transport History, vol. 27, no. 2 (September 2006), pp. 97113. vol. 27, no. 2 (September 2006), pp. 97113.

"less crowded roads elsewhere": Brian D. Taylor, "Rethinking Traffic Congestion," Access Access (October, 2002), pp 816. (October, 2002), pp 816.

boosts productivity: Timothy F. Harris and Yannis M. Ioannides, "Productivity and Metropolitan Density," Dept. of Economics, Tufts University, 2000, http://ase.tufts.edu/econ/papers/200016.pdf.

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

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

close to $12 billion: This, and the $108 billion figure, come from Gabriel Roth, ed., Street Smart: Compet.i.tion, Entrepreneurship, and the Future of Roads Street Smart: Compet.i.tion, Entrepreneurship, and the Future of Roads (New Brunswick: Transaction Publishers, 2006), p. 7. (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 inst.i.tutions 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, Transportation Science, vol. 39 (2005), pp. 44650. vol. 39 (2005), pp. 44650.

J. G. Wardrop: J. G. Wardrop, "Some Theoretical Aspects of Road Traffic Research," Proceedings of the Inst.i.tute of Civil Engineers, Part II Proceedings of the Inst.i.tute of Civil Engineers, Part II (1952) pp. 32578. (1952) pp. 32578.

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

really makes the head spin: When I asked Anna Nagurney, an expert in networks at the University of Ma.s.sachusetts 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 Selfish Routing and the Price of Anarchy (Cambridge, Ma.s.s.: MIT Press, 2005). (Cambridge, Ma.s.s.: 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 http://ssrn.com/abstract=424244.

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, Journal of Transport Economics and Policy, January 1995, pp. 732. 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. January 1995, pp. 732. 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, Journal of Transportation and Statistics, vol. 1, no. 3 (October 1998), pp. 124. vol. 1, no. 3 (October 1998), pp. 124.

rates and speeds: William T. Hughes Jr. and C. F. Sirmans, "Traffic Externalities and Single-Family House Prices," Journal of Regional Science, Journal of Regional Science, vol. 32, no. 4 (1992), pp. 487500. vol. 32, no. 4 (1992), pp. 487500.

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, American Journal of Respiratory and Critical Care Medicine, vol. 164 (2001), pp. 217780. 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? vol. 164 (2001), pp. 217780. 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 gra.s.sland birds in Ma.s.sachusetts 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 Gra.s.sland Bird Patterns in a Suburbanizing Landscape," Environmental Management, Environmental Management, vol. 29 (2002), pp. 782800, and R. T. T. Forman, et al., vol. 29 (2002), pp. 782800, and R. T. T. Forman, et al., Road Ecology: Science and Solutions 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 (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, 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. 1317. eds. C. L. Irwin, P. Garrett, and K. P. McDermott (Raleigh: Center for Transportation and the Environment, North Carolina State University, 2006), pp. 1317.

less able to afford cars: See Donald Appleyard, M. Sue Gerson, and Mark Lintell, Livable Urban Streets: Managing Auto Traffic in Neighborhoods, 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 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 http://www.transalt.org/press/releases/061004trafficshumantoll.htm.

were taxing the poor: It follows that poorer areas also suffer more exposure to the exhaust of pa.s.sing 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, Science, December 13, 1968. December 13, 1968.

oft-invoked "tragedy": Shi-Ling Hsu, "What Is Is a Tragedy of the Commons? Overfishing and the Campaign Spending Problem," February 21, 2005, bepress Legal Series, Working Paper 463; a Tragedy of the Commons? Overfishing and the Campaign Spending Problem," February 21, 2005, bepress Legal Series, Working Paper 463; http://law.bepress.com/expresso/eps/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, Wall Street Journal, August 28, 2007. August 28, 2007.

all those fuel taxes: Mark Delucchi of the Inst.i.tute 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?" Inst.i.tute 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, Wall Street Journal, August 1819, 2007. August 1819, 2007.

"90 percent of the time": Martin Wachs, "Fighting Traffic Congestion with Information Technology," Issues in Science and Technology, Issues in Science and Technology, vol. 19 (2002), pp. 4350. vol. 19 (2002), pp. 4350.

two Canadian researchers: See K. Mucsi and A. M. Khan, "Effectiveness of Additional Lanes at Signalized Intersections," Inst.i.tute of Transportation Engineers Journal, Inst.i.tute of Transportation Engineers Journal, January 2003, pp. 2630. 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." January 2003, pp. 2630. 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 overpa.s.ses, 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 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 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 http://www.abmb.com/cfi.htm.

an estimated 12.7 percent: This number is taken from H. Teng and J. P. Masinick, "An a.n.a.lysis 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 Sch.e.l.ling, Micromotives and Macrobehavior Micromotives and Macrobehavior (New York: W.W. Norton, 2006), p. 125. (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, National Post, July 18, 2007. 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 s.p.a.ce." From Harford, The Undercover Economist The Undercover Economist (Oxford: Oxford University Press, 2004), p. 88. (Oxford: Oxford University Press, 2004), p. 88.

more people want to use them?: William Vickrey, "Pricing in Urban and Suburban Transport," American Economic Review, American Economic Review, vol. 53 (1963). Reprinted in Richard Arnott, Kenneth Arrow, Anthony B. Atkinson, and Jacques H. Dreze., eds., vol. 53 (1963). Reprinted in Richard Arnott, Kenneth Arrow, Anthony B. Atkinson, and Jacques H. Dreze., eds., Public Economics: William Vickrey Public Economics: William Vickrey (Cambridge: Cambridge University Press, 1994). (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 www.economics.missouri.edu/working-papers/2005/wp0519_harstad.pdf.

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, Journal of Consumer Research, vol. 31 (2004), pp. 31323. vol. 31 (2004), pp. 31323.

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 www.richardclegg.org/pubs/rgc_utsg2005.doc.

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, Wall Street Journal, February 5, 2007. February 5, 2007.

jump by 5 percent: Philip Bagwell, The Transport Revolution The Transport Revolution (London: Rout-ledge, 1988), p. 375. (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, Access, vol. 26 (2005), pp. 1015. vol. 26 (2005), pp. 1015.

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 ma.s.sive 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 cla.s.sic "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 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. 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," it is expensive: See, for example, Daniel Machalaba, "Paying for VIP Treatment in a Traffic Jam," Wall Street Journal, Wall Street Journal, June 21, 2007. June 21, 2007.

as the toll goes up: As Moshe Ben-Akiva, director of the Intelligent Transportation Systems program at the Ma.s.sachusetts Inst.i.tute 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 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." 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; http://repositories.cdlib.org/its/path/papers/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 http://ssrn.com/abstract=393841.

flocked to the highway: Virginia Groark, "Dan Ryan Traffic Flow Changes by Minute-Like Chicago Weather," Chicago Tribune, Chicago Tribune, April 5, 2006. 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, Transportation Research A, vol. 25A, no. 5 (1991), pp. 25166. vol. 25A, no. 5 (1991), pp. 25166.

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

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

to the same problem: There is an interesting a.n.a.logy 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, 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," 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, The Journal of Economic Perspectives, vol. 15, no. 7 (Winter 2001), pp. 4154. vol. 15, no. 7 (Winter 2001), pp. 4154.

"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, Seattle Times, August 22, 2007. 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, Ma.s.sachusetts Inst.i.tute of Technology, 1992).

travel times and congestion: See, for example, Daniel Florian, "Simulation-Based Evaluation of Advanced Traveler Information Services (ATIS)" (dissertation, Ma.s.sachusetts Inst.i.tute 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, Transportation Research Part C, vol. 11 (2003), pp. 7587. vol. 11 (2003), pp. 7587.

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. 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. Mahma.s.sani and R. Jayakrishnan, "System Performance and User Response Under Real-Time Information in a Congested Traffic Corridor," 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. Mahma.s.sani and R. Jayakrishnan, "System Performance and User Response Under Real-Time Information in a Congested Traffic Corridor," Transportation Research A, Transportation Research A, vol. 25, no. 5 (1991), pp. 293307. See also R. Arnott, A. de Palma, and R. Lindsey, "Does Providing Information to Drivers Reduce Traffic Congestion?" vol. 25, no. 5 (1991), pp. 293307. See also R. Arnott, A. de Palma, and R. Lindsey, "Does Providing Information to Drivers Reduce Traffic Congestion?" Transportation Research A, Transportation Research A, vol. 25, no. 5 (1991), 30918, and A. M. Bell, W. A. Sethares, and J. A. Bucklew, "Coordination Failure as a Source of Congestion," vol. 25, no. 5 (1991), 30918, and A. M. Bell, W. A. Sethares, and J. A. Bucklew, "Coordination Failure as a Source of Congestion," IEEE Transactions on Signal Processing, IEEE Transactions on Signal Processing, vol. 51. no. 3, March 2003. vol. 51. no. 3, March 2003.

congestion has been pa.s.sed: 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, Physica A, vol. 363, no. 1 (2006), pp. 8995. vol. 363, no. 1 (2006), pp. 8995.

because they are the fastest: A similar dynamic, interestingly, exists in ant-trail formation. As noted in the book Self-Organization in Biological Systems, 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 Deneoubourg, Nigel R. Franks, et al., 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 Deneoubourg, Nigel R. Franks, et al., Self-Organization in Biological Systems Self-Organization in Biological Systems (Princeton: Princeton University Press, 2001), particularly Chapter 13. (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, Daily Telegraph, June 11, 2006. 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, Operations Research, vol. 50, no. 1 (JanuaryFebruary 2002), pp. 17378. vol. 50, no. 1 (JanuaryFebruary 2002), pp. 17378.

Chapter Seven: Why Dangerous Roads Are Safer.

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

year before the changeover: See R. Naatanen and H. Summala, Road-User Behavior and Traffic Accidents Road-User Behavior and Traffic Accidents (New York: Elsevier, 1976), pp. 13940. (New York: Elsevier, 1976), pp. 13940.

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 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 ITE Annual Meeting Compendium (Washington, D.C.: Inst.i.tue for Transportation Engines, 2000). (Washington, D.C.: Inst.i.tue 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, American Journal of Public Health, vol. 91, no. 4 (April 2001), pp. 62831. vol. 91, no. 4 (April 2001), pp. 62831.