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Our Need for Speed

Seat Belts, Air Bags and Anti-Lock Brakes Have Made Cars Safer, But There's One Problem Engineers Can't Solve: the Driver

August 29, 2004|Sanjiv Bhattacharya | Sanjiv Bhattacharya's last story for the magazine was about a simulated Mars space station.

In 1981 the German Transportation Ministry conducted an experiment into the effectiveness of anti-lock braking systems, only to discover that no brakes can stop the hurtling imbecility of human nature.

The ministry fitted half of the 91-car Munich taxi fleet with anti-lock brakes, which at the time were considered a major leap in road safety. Then it monitored the fleet for three years using accelerometers, which measure G-forces, and undercover passengers. Every care was taken to avoid corruption of the data--the drivers were switched among the cars, for example, and they were not told which cars had anti-lock brakes nor how they would be monitored. The results were clear. Not only did drivers of ABS-equipped vehicles have slightly more accidents, on average, they also tended to brake harder, accelerate faster and create more traffic conflicts. In other words, the wonder brakes did nothing for road safety, but rather had the opposite effect: They encouraged drivers to speed up and be more reckless.

Granted, German cabbies represent only a small number of all road users, but nevertheless their behavior raises a number of questions about road safety, psychology and, ultimately, the way human beings are wired. Does this happen with all car safety features? Do we thwart them, albeit inadvertently? Maybe this is the tension of evolution--as science urges us to higher ground, our grubby animal nature tugs the other way. But why does the animal so often win?

According to Gerald Wilde, a Dutch psychologist now living in Ontario, Canada, the Munich experiment is best examined through the prism of risk. In his 1994 book "Target Risk"--since updated to "Target Risk 2" in 2001 and with a third installment on the way--he argues that the cab drivers were exhibiting "risk homeostasis," or our tendency as a species to maintain an optimum level of risk in our lives. The theory holds that when we feel safer because of anti-lock brakes, condoms or childproof bottle tops, to cite just a few examples, humans compensate with riskier behavior, such as driving faster, having sex with more strangers or being less vigilant in monitoring children's access to medicine. The result is the same in many scenarios--the accident rate remains relatively unaffected despite the best efforts of scientists and legislators to reduce it. For Wilde, "safety features" are nothing of the sort.

The numbers are compelling. In the United States between 1923 and 1996, the number of annual road deaths per 100,000 residents has not shown the steady decline one might expect, but rather has fluctuated at about 23, on average. Though there has been a net decrease in accidents since the early 1970s, the graph is jagged, and the fluctuations bear no apparent correlation to the advent of seat belts, air bags or anti-lock brakes. This is not to say that cars today aren't safer, because they are. Per mile driven, the fatality rate has dropped twelvefold in the same period. But today we drive more miles, crowd the freeways with more cars and drive faster--so many of us are still dying, per capita, as often as we did in the Jazz Age.

The logic seems intuitive at first: A perception of safety encourages risk-taking, just as a sense of danger encourages caution. In an uninsured, rusty jalopy with a busted windshield and dodgy brakes, a driver usually is on full alert, if only to watch for cops. But tuck that driver into a new Volvo, surrounded by state-of-the-art air bags, comforted by a small insurance deductible and reassured by the tug of the seat belts, and there's a decent chance he'll wind up in a hedge, or worse.

Studies show that a sense of safety lulls us into danger, hampering the effectiveness of pedestrian crosswalks and low-nicotine cigarettes. It also explains why the number of flooding deaths per capita in America hardly changed between 1906 and 1985, despite the construction of stronger levees in at-risk flood plains. Many people moved into the flood plains thinking that the new levees made them safe. When floods did occur, their impact was much greater.

The lull, however, is only one factor in keeping our risk level high. Another is our appetite for thrills and brinkmanship, as shown by the Munich taxi drivers. A study in 2000 by a graduate student at Western Oregon University showed that recently improved parachute rip cords did not reduce the number of skydiving accidents. Instead, a new spate of accidents emerged, caused by skydivers pulling the rip cord too late. The end result was that the accident level remained unchanged.

Perhaps this is the work of natural selection, the ruthless culling that permits survivors to label the dead as unfit. Or alternatively, risk homeostasis may be stalling our evolutionary ascent. No matter how "safe" our systems, we have the weight of human fallibility dragging us down.

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