The Effects of Rain on Traffic Safety and Operations on Florida Freeways

Although the association between weather and traffic variables or crash events appear intuitive to motorists, quantifying the effects that weather, especially rain, has on driver response in travel speeds, traffic demands, and susceptibility of accident occurrence is needed to evaluate practical aspects of traffic operations and safety measures. Previous studies have researched driver responses to inclement weather on roadways located primarily in northern and western regions of the United States (U.S.), Canada, and Europe. However, driver familiarity to local weather conditions is a factor that should be considered in determining inclement weather effects on traffic variables and crash occurrence. This research focused on the effects of rain precipitation on freeways located in the Southeast region of the U.S. to determine if results from previous studies are general indicators or location specific in nature. The impacts of rain on hourly mean speeds and traffic volumes were studied for freeway segments in Jacksonville, Florida. Results indicate significant reductions in both traffic parameters with increasing rain intensity. Crash data examined along the same freeway sections found that hourly crash risks and crash rates per 100 million vehicle miles of travel, based on rain exposure hours, increased with increasing rain intensity, and were significant. However, hour-of-day and season of year had little effect on hourly crash occurrence. Rain intensity also significantly increased the proportion of injury accidents in the majority of traffic conditions.