Buckle up or slow down? New estimates of offsetting behavior and their implications for automobile safety regulation

This study provides a detailed examination of the determinants of motor vehicle fatalities and offers a new assessment of the effects of automobile safety regulation. An empirical analysis is difficult because drivers are unlikely to remain passive in the face of changes in their safety environment. This offsetting behavior hypothesis is cast in a broad framework that brings together elements from the economics and cognition literatures. This approach allows us to highlight key maintained assumptions in previous analyses and to consider how econometric evidence can inform discussions about highway safety policy. The econometric estimates reveal that, while imprecisely estimated, offsetting behavior is quantitatively important and attenuates the effects of safety regulation on total motor vehicle fatalities. Cognitive elements, the relative costs of repairs, and the functional form of the estimating equation are shown to play prominent roles in the analysis of safety regulation. Our estimates imply that current highway policy initiatives-mandating restraint systems and relaxing restrictions on the maximum speed limit-are likely to have only a modest net effect on reducing motor vehicle fatalities.