The Cost of Weather-Related Traffic Collisions

Abstract Traffic collisions are the leading causes of death and injury worldwide, and society is prioritizing policies to reduce these outcomes. Weather conditions contribute to traffic collisions in complex ways, while finite budgets and political realities limit the infrastructure and policy actions that decision-makers can use. To efficiently address this issue, decision-makers and the public need actionable information on factors affecting traffic collision rates at the scale of the local political unit where beneficial action is most plausible. To that end, this study analyzes daily county-level traffic collisions and casualties in the American state of North Carolina over the years 2013–19. We identified an average of 7805 excess collisions and $961 million in social costs each year due to commonplace adverse weather events and conditions such as precipitation, wind, and temperature extremes. The majority of these weather-related outcomes correspond to precipitation and winter storms, significant given projected increases in both due to climate change. We also find reduced collisions following adverse weather. At a granular level, adverse weather costs individual counties thousands to millions of dollars per exposure due to excess collisions, justifying policy efforts related to communication, infrastructure, and enforcement to reduce these negative outcomes. We find significant variability in risk for different road user groups, including pedestrians and bicyclists, and heterogeneity in county-level outcomes relative to statewide trends for specific causes. Our study highlights the practical challenges of studying and addressing traffic collisions and road safety and provides suggestions for decision-makers. Significance Statement The purpose of this study is to identify the cost of weather as it relates to traffic collisions and the social cost of casualties, property damage, and congestion. In policy efforts, this baseline can serve as the cost of inaction or the cost of the status quo and is an effective benchmark for evaluating candidate policy actions. This study finds that commonly occurring adverse weather conditions and events have disparate impacts on collision outcomes for vehicles, bicycles, and pedestrians, with significant social costs that range from thousands to millions of dollars per day of exposure at the county level.