Traffic collisions are a significant cause of death and injury worldwide, with complex causal factors that frustrate mitigation efforts. Adverse weather impacts on traffic collisions are broadly known, but actionable data is lacking for how weather interacts with the built environment and road users at the local level. Our research addresses that knowledge gap, finding heterogeneous weather-related collision outcomes and associated social costs across North Carolina.
Seven years of daily county-level traffic outcomes and weather conditions were modeled to identify excess collisions attributable to common adverse conditions of rain, winter weather, flooding, and wind, as well as extreme events such as cyclones and tornadoes. Established social costs of traffic collisions were then used to calculate the economic impact of weather through traffic collisions, a burden we found to average nearly $1 billion per year. State-wide, precipitation is the most common exposure and had the highest total cost at $471 million per year, while winter events have the highest average exposure cost at $186,000 per county per day. County exposure costs tend to scale with population, but more populous counties do proportionally worse with winter weather, followed by flooding, wind, and then rain. In total, annual social costs of weather-related traffic collisions range between $27 and $202 per-capita depending on county.
We further studied these collisions from the perspective of road user groups, finding that outcomes change heterogeneously for all road user groups when exposed to adverse conditions. Of note, cargo trucks are the most impacted user group by flooding and thunderstorm derived winds, farm vehicles are the most impacted by straight line winds, while emergency service vehicles see the largest increase in counties exposed to cyclones, winter weather, and tornadoes. Over our study period, collisions increased for all road user groups except for bicycles and motorcycles, with faster than average increases among emergency vehicles, cargo trucks, and large passenger vehicles. Notably, we found a reduction in collisions in days following adverse weather.
Road infrastructure, public education, and law enforcement are the most common pathways for addressing road safety and moving towards goals such as Vision Zero, and we make the case that heterogeneity in weather-related outcomes by county and road user groups indicate new potential risk management pathways for reducing traffic collisions. Given the disparity between county-level and state-level results, our work highlights the challenges that local governments face in addressing traffic safety within their borders, especially with dynamic populations and changing weather exposures.
Future research would benefit from high spatial and temporal granularity, as well as ensuring complete exposure and outcome data is used.—Iain Burnett (North Carolina State University), and Jane Harrison, “The Cost of Weather-Related Traffic Collisions,” in the July issue of Weather, Climate, and Society.
