Heat Waves and Road Traffic Collisions in Alabama, United States

The effects of heat waves on traffic collisions require investigation to improve traffic safety during extreme heat events. A time-stratified case-crossover design was used to examine associations between heat waves and traffic collisions in Alabama between May and September from 2009 to 2018. We derived a heat wave index, defined as the daily mean temperature greater than the 95th percentile for two or more consecutive days, by meteorological data from Phase 2 of the North American Land Data Assimilation System. We obtained traffic collision records from the Alabama Department of Transportation. A nonsignificant and negative association between traffic collisions and heat waves was noted, with a 1.4 percent decrease (95 percent confidence interval [CI] [−3.1 percent, 0.4 percent]) in traffic collisions on heat wave days compared to non–heat wave days. Similar results were found when the analysis was stratified by driver-related factors (i.e., gender, age, race, employment status, and driver residence distances), vehicle-related factors (i.e., vehicle usage), and collision-related factors (i.e., rural or urban roads, speed limits, and intersections). A significant and positive association was observed on heat wave days without precipitation, however (23.5 percent increase; 95 percent CI [7.3 percent, 42.3 percent]). In conclusion, traffic collisions were not associated with heat waves in many collision-related conditions in Alabama.