Weather, Traffic Accidents, and Climate Change

We exploit random daily variation in weather to document the relationship of temperature, rainfall, and snowfall with traffic accidents and travel demand. Using information on 46.5 million accidents from the State Data System of police reported accidents for 20 states and travel demand for 207,455 households included in the National Household Transportation Survey, we find unanticipated effects of weather on accidents and their severity. Our estimates suggest that while warmer temperatures and reduced snowfall are associated with a moderate decline in non-fatal accidents, they are also associated with a significant increase in fatal accidents. This increase in fatalities is due to a robust positive relationship between fatalities and temperature. Half of the estimated effect of temperature on fatalities is due to changes in the exposure to pedestrians, bicyclists, and motorcyclists as temperatures increase. The application of these results to middle-of-the-road climate predictions suggests that weather patterns for the end of the century would lead to 603 additional fatalities per year. Between 2010-2099, the present value social cost of all types of accidents caused by climate change is $58 billion.