Issn 1045-6333 the Effects of Mandatory Seat Belt Laws on Driving Behavior and Traffic Fatalities

This paper investigates the effects of mandatory seat belt laws on driver behavior and traffic fatalities. Using a unique panel data set on seat belt usage rates in all U.S. jurisdictions, we analyze how such laws, by influencing seat belt use, affect traffic fatalities. Controlling for the endogeneity of seat belt usage, we find that it decreases overall traffic fatalities. The magnitude of this effect, however, is significantly smaller than the estimate used by the National Highway Traffic Safety Administration. Testing the compensating behavior theory, which suggests that seat belt use also has an adverse effect on fatalities by encouraging careless driving, we find that this theory is not supported by the data. Finally, we identify factors, especially the type of enforcement used, that make seat belt laws more effective in increasing seat belt usage. and seminars participants at Harvard University for helpful comments. We thank the NHSTA and the Highway Safety Offices of many states for providing us with the data on seat belt usage rate. Any remaining errors are our own.