Presented in this paper is a detailed investigation of highway traffic variations with severity of cold, amount of snow and various combinations ofcold and snow intensities. Separate analysis for starting, middle and ending months of winter seasons is conducted to understand the variations in traffic-weather relationships within the winter season. The study is basedon hourly traffic flow data from 350 permanent traffic counter sites located on the provincial highway system of Alberta, Canada, and weather data obtained from nearby Environment Canada weather stations, 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 aninteraction 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 flowwith cold and snow varies with day of week, hour of day and severity of weather conditions. 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. Study results show lesser impact of adverse weather conditions on highway traffic volumes during severe winter months and the months thereafter as compared to starting months.
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