Association of Highway Traffic Volumes with Cold and Snow and Their Interactions.

Presented in this paper is the association of highway traffic flow with severity of cold, amount of snow and various combinations of cold and snow intensities by giving detailed consideration to factors such as highway type and location. The study is based on hourly traffic flow data from 350 permanent traffic counter sites located on the provincial highway system of Alberta, Canada, and weather data obtained from Environment Canada weather stations located within 10 miles of the selected permanent traffic counter sites, during the period of 1995-2005. Multiple regression analysis is used in the modeling process. The model parameters include three sets of variables: amount of snowfall as a quantitative variable, categorized cold as a dummy variable and an interaction variable formed by the product of the above variables. The developed models closely fit the real data with R-square values greater 0.99. The study results indicate that the association of highway traffic flow with cold and snow varies with day of week, hour of day and severity of weather conditions. Traffic volume on a day decreases with the increase in severity of cold and snow. A reduction of 1% to 2% in traffic volume for each centimeter snowfall is observed when the mean temperatures are above 0°. For the days with zero precipitation, reductions in traffic volume due to mild and severe cold are 1% and 31%, respectively. An additional reduction of 0.5% to 3% per each centimeter of snowfall results when snowfall occurs during severe cold conditions.