Sometimes a perfectly good theory can sound nuts. Take this one: Safer cars make the roads less safe.
Sounds as loony as the one about how you're better off not wearing a seat belt, right?
But the first statement is, in fact, a lot more credible -- and it leads to some interesting debate about driving behavior, accident rates and, ultimately, how insurance rates are calculated.
It's called the Peltzman Effect, a generally accepted principle that suggests that as people feel safer they take on greater risk. People have a set tolerance level for risk and adjust their behavior accordingly. Build a high-impact football helmet, and players will ram their heads harder. Improve car safety, and people will drive faster.
The danger comes when the added risk cancels out the benefits of the safety measures or, worse, adds new and greater risks. In football, for example, evidence is mounting that the fierce head butts of the modern game are causing long-term brain damage.
And it's increasingly clear that we feel safe enough in our cars to consume a meal, phone a friend or argue with our passengers at 75 mph.
So what if I crash?
University of Chicago economist Sam Peltzman conceived the theory in 1975 after finding that accident rates had remained stagnant in the 1960s following the introduction of federal auto safety regulations. When drivers felt protected, they drove more recklessly, Peltzman concluded, putting pedestrians, cyclists and others at greater risk.
In the years since, vehicular fatality rates have dropped dramatically even as safety laws have mounted, refuting the notion that the Peltzman Effect offsets the benefits as a whole.
"There is some evidence that safety features that people get direct feedback from do cause them to drive less carefully, and the best example is studded snow tires," says Russ Rader, spokesman for the Insurance Institute for Highway Safety. "But there's no evidence that this is widespread with things that don't give drivers direct feedback, like airbags" and electronic stability control.
In 1980, three years before the first state mandatory seat belt law went into effect, 51,091 people were killed in auto crashes in the U.S., a rate of 3.345 per 100 million vehicle miles traveled (VMT). In 2010, an estimated 32,788 were killed, a rate of 1.09 deaths per VMT. (For a graphic illustration of how times have changed, check out this test crash of a 1959 Chevy with a 2009 Chevy. Hint: the driver of one would have been killed instantly; the driver of the other would have sustained a knee injury.)
"If it were affecting drivers significantly, then we would not have seen the dramatic reductions in crashes and fatalities that have occurred over the last 50 years, since auto safety regulations were first implemented," Rader says.
A knife at your throat
The Peltzman Effect has been difficult to prove, given the number of variables that exist both in cars and on the roads, yet experts still joke that the safest cars would be those with unrestrained drivers facing a dagger on the steering column.
In 2007, two university economists turned to what they considered an objective, highly controlled laboratory: NASCAR. After parsing track data from 1972 to 1993, the researchers confirmed the Peltzman Effect. As cars became safer, racers drove more recklessly. Safer cars equaled more crashes.
The total number of injuries also decreased, however, although not by as much if drivers had not compensated with riskier behavior. (In fact, researchers cited a dual benefit to NASCAR given that crashes increase viewership.)
But everyday drivers don't get prize money. They get auto insurance discounts just for having the safety devices aboard. They get the chance to take more chances another day. And they get a better shot at surviving the accidents that technology can't avoid.
So what happens off the racetrack? Here, too, multiple studies have found that drivers tend to behave in a riskier or more aggressive fashion when they believe themselves better protected -- either with anti-lock brakes, four-wheel drive, studded snow tires, or simply larger vehicles.
The Peltzman Effect Gone Wild
That spells trouble for everyone else, particularly those in small cars that sustain greater damage in a collision with a pickup or SUV.
In a 2008 study at West Virginia University analyzing national fatal crash data from 1995 through 2006, researchers found that SUVs were 2.7 times more likely to cause an accident than passenger cars.
In addition, researchers are now starting to find that semi-automated safety devices, such as those that monitor distance from another vehicle, threaten to breed a dangerous complacency behind the wheel. "It could be the Peltzman Effect gone wild," says Janos Wimpffen, owner of Sports Car Racing Research Associates, a transportation consultancy.
"If everyone had fairly fragile, small cars, it's likely that their driving behavior would be somewhat more defensive. They would understand that were they to get into an accident the consequences would be more severe," Wimpffen says. "The opposite of that is people who have very big cars may take greater risks."