Subtle impact: airbags' effect on driving behavior.

Airbags' effect on driving behavior

Airbags save lives. At least that's the conventional wisdom, and why airbags have been mandated by the federal government. In a front-end collision, airbags do significantly reduce fatalities - by 24 percent over seat belts, according to a study by the Insurance Institute for Highway Safety.

But, says Steven Peterson, professor of economics at Virginia Commonwealth University, "An airbag allows me to drive more aggressively but not face any more risk." In fact, drivers of airbag-equipped cars get into and cause more accidents, negating the safety benefits for drivers and increasing the risk to others.

Peterson and his colleagues George Hoffer and Edward Millner tested the so-called offsetting behavior hypothesis in the October 1995 issue of The Journal of Law and Economics. The study found that airbag-equipped cars for model years 1989-1993 had higher personal injury claims and collision claims than non-airbag models for the same years.

The authors also examined all fatal driving accidents in Virginia from 1993 involving post-1989 model year passenger vehicles, and discovered that drivers with an airbag were more likely to be killed than drivers without one. In 48 percent of the single-car accidents in which only the driver was killed, that person was driving an airbag-equipped car. But cars with an airbag account for only 44 percent of post-1989 cars. Most single-car accidents are head-on collisions, and airbags are supposed to reduce fatalities in those cases by 24 percent. Based on these probabilities, drivers protected by an airbag should represent only 33 percent of those fatalities.

In fatal accidents involving a car with an airbag and a car without one, the driver behind an airbag was at fault nearly three-quarters of the time. The passengers and the driver of the other car usually bore the brunt of the impact.

"The driver with an airbag walked away most of the time. But the passengers and the folks in the other car didn't," says Peterson.

These results are also consistent with "buyer sorting," which holds that drivers who are more likely to get into accidents will buy safer cars disproportionately. However, if that were the case, says Peterson, researchers would expect to find higher accident rates in the first models to adopt airbags, as the most dangerous drivers purchased the safest cars. But the study found no such trend for personal injury and collision claims, strongly suggesting that good drivers go bad - and bad drivers get worse - behind an airbag.

"Maybe insurance companies should place a surcharge on premiums rather than offering a discount for airbag-equipped cars," says Peterson.