Probabilistic Modeling of Inclement Weather Impacts on Traffic Volume

Inclement weather may potentially create traffic flows and driving behaviors that differ from those behaviors observed under normal conditions. Depending on weather type, severity, and duration, roadways may not perform to their optimal capabilities and driver ability may be challenged. To this end, researchers have studied reductions in supply parameters (e.g., capacity and speeds) due to inclement weather conditions. Current studies have underrepresented the effect of inclement weather on demand parameters. This study proposes a probabilistic approach to determine the percent average reduction of traffic demand under both rain and snowfall conditions. This demand reduction is further differentiated by the time of day of inclemency and by the relative severity inclement weather. This research studied seven sites surrounding major central business districts in Virginia and Minnesota and found that (a) rain and snowfall have varying impacts on travel demand, (b) time of day is an important factor to consider because of the likelihood of discretionary and non essential trips occurring at specific hours of the day, and (c) snowfall, as expected, produces much bigger impact on traffic volume than rainfall.