Fred Mannering, Ph.D.,
Title: Analysis of Drivers' Risk Compensation Response to Vehicle Safety Features
Abstract: The past decade has seen incredible advancements in vehicle safety technologies. For example, front and side airbag systems, antilock braking systems, traction control, and electronic stability control have become pervasive features in a significant portion of our nation's vehicle fleet. From a technical perspective, the expectation would be that the introduction of these features would greatly reduce the likelihood of accidents in general and injury-causing accidents in particular. But aggregate accident data do not necessarily show this. Fatalities have stayed nearly constant in recent decades. And, in 2005, the number of fatalities per mile driven increased for the first time in nearly 20 years (although the fatality rate again declined slightly in 2006).
One possible explanation for why the consistently high number of fatalities and fatality rates have not substantially declined is that drivers are using the safety features to drive more aggressively, thus offsetting safety impacts of these features.
The offset hypothesis predicts that individuals will adapt to innovations that improve safety by becoming less vigilant about safety. Previous tests of this hypothesis to highway safety have used aggregated data which limit predictability because such data cannot account for self-selectivity (the tendency of high-risk or low-risk drivers being more or less likely to own a vehicle with enhanced safety features). Our research tests the offset hypothesis by using disaggregate data to analyze the effect of airbags and antilock brakes on automobile safety.
Using a simultaneous discrete modeling approach, we statistically model the probability of individuals having an injury-producing accident, and owning a vehicle with airbags and/or antilock brakes. We find that airbags and antilock brakes have no statistically significant effect on the likelihood of an accident or its injury severity, suggesting that drivers are trading off enhanced safety for speedier trips.
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