Adverse Weather Conditions and Motor Vehicle Fatalities in the United States: Current Burden and Implications from Climate Change
Shubhayu Saha Paul J. Schramm Amanda Nolan
Background Motor vehicle crashes are a major cause of mortality in the United States and are the leading cause of death for those aged 12-19. Among different factors that affect fatal crashes, adverse weather is an important risk factor. Future climate projections indicate changing precipitation patterns across the country. Shifts in frequency, seasonality, and intensity of precipitation could affect motor vehicle crashes and have public health implications.
Objectives To examine the current public health burden of weather-related crash fatalities and spatial and temporal variation in risk for such fatalities to inform strategies to identify vulnerabilities resulting from projected precipitation changes.
Methods Using data from the National Highway Traffic Safety Administration's Fatality Analysis Reporting System (FARS), we aggregated the counts of motor vehicle fatalities associated with precipitation and weather-related adverse road surface conditions in the United States from 1994-2011. We examined the seasonal distribution of these crashes for each of the different weather exposures associated with each fatality. We also obtained annual data on population and vehicle miles traveled (VMT) for each state, and calculated average fatalities per VMT over the study period. We obtained climate projection information from NARCCAP and CMIP3 models used in the US National Climate Assessment and calculated state-level average change in precipitation levels in 2041-2070 compared to the current baseline.
Results/Discussion On average, 17% of all motor vehicle crash fatalities occurred during adverse weather (rain, snow, sleet) or when road conditions were wet or icy. Potential confounding factors such as alcohol/drug use and driver age were assessed and do not appear to affect the fatality rate during adverse weather. While the overall number of deaths due to motor vehicle crashes has steadily declined over the last two decades, the proportion associated with adverse weather has remained relatively constant. Geographically, the Southwestern US had the fewest weather-related fatalities per VMT, while the Northwest and Central Atlantic regions had the most fatalities per VMT. A spatial comparison of current weather-related crash burden and future expected precipitation levels was conducted. Projected increases in total yearly precipitation amounts in the Northeast, North Central, and Eastern Seaboard regions coincide with already elevated fatalities in these areas. While the impact of precipitation increase is speculative, there is potential for a shift in the public health burden of weather-related motor vehicle crashes, particularly in regions with an already large burden. Conversely, areas in the Southwest that already have a relatively low weather-related motor vehicle fatality rate are expected to receive even less precipitation by mid-century.
Conclusions The data indicates that weather-related motor vehicle fatalities are a serious public health problem, with the health burden varying both seasonally and geographically. Some areas of the country may experience changes in climate and weather that could affect motor vehicle crash fatality burden. Further study is needed to classify the impact that climate change will have on weather-related motor vehicle crash fatalities.