The effect of population safety belt usage rates on motor vehicle-related fatalities.

The effectiveness of safety belt usage in reducing mortality and morbidity among traffic crash victims has been well established. Population safety belt usage rates have been increasing from 11% in 1980 to 68% in 1995, as measured by observational surveys sponsored by the National Highway Traffic Safety Administration (NHTSA). Safety incentive grants from NHTSA to the States with higher than average usage rates are expected to total $500 million during 1999-2003. In this paper, longitudinal annual motor vehicle-related fatality levels are analyzed by state to estimate the effect of the population safety belt usage rate on traffic fatality rates in the presence of known confounders such as alcohol use and youthful drivers. Consideration of alternative models applied to 14 years of data shows that the population safety belt usage rate (at least, at the current rates) is associated with little or no effect on reducing fatality rates. On the other hand, higher safety belt usage rates arising from states with primary enforcement laws tend to suggest reductions in fatality rates. Such results call into question the NHTSA policy of basing incentive programs on overall safety belt usage rates.