Reversal of the road death trend in the U.S. in 2015–2016: An examination of the climate and economic hypotheses

Abstract

Abstract Previous research attributed the reversal in the trend of road death rates in the U.S. during 2015 primarily to increase in road use related to higher temperature but another study said it was due to reduced unemployment. Road deaths increased again during 2016 extending the reversal. This study examines the association of road deaths per population among the 48 contiguous U.S. states to average annual temperature, precipitation, unemployment, insurance cost, gasoline prices, registered vehicles per population, mix of types of vehicles and median age of the population using logistic regression. Least squares regression is used to examine the association of miles traveled per vehicle to average annual temperatures, unemployment, insurance costs and gasoline prices. The association of national unemployment trend and road death trend is examined using least squares regression. Per population, road deaths are more frequent where average monthly temperatures are higher consistently from year to year. Predictions of road deaths using only national trends in unemployment and vehicle miles traveled are unreliable. The association of unemployment with road deaths per population among U.S. states is different in recessions than when the economy has largely recovered. When unemployment is declining, road deaths are reduced, other thing being equal, likely due in part to increased sales of new vehicles with improved safety technology as prosperity increases. Miles driven per vehicle among U.S. states are higher in warmer states but are unrelated to unemployment, insurance costs, and gasoline prices. Teenaged licensure declines as insurance costs, gasoline prices and unemployment increases in selected years. The increase in deaths during 2015–2016 was mainly related to warming temperatures, lower gasoline prices and increased use of trucks as a percent of registered vehicles, not reduced unemployment.