Traffic (57 page)

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

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

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

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

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

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

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

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

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

50 years of driving: Data retrieved on May 5, 2007, from
http://hazmat.dot.gov/riskrngmt/riskcompare.htm
.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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