Impacts of Snowfall, Low Temperatures, and their Interactions on Passenger Car and Truck Traffic
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Winter weather conditions such as extremely cold temperatures, heavy snowfall, and high wind chills are common occurrences in Canada and many other countries around the world. Impacts of such adverse weather conditions on total highway traffic volume have been the subject of numerous research studies in the past. However, none of the past studies investigated thoroughly the impacts of severe cold and heavy snow fall on temporal and spatial variations of truck traffic on Canadian highways. Impacts of weather on route choice behaviour of truck and passenger car drivers have also not been addressed in the past. A detailed investigation was carried out in this study to understand and analyze traffic flow variations during severe winter weather, including development of models of cold and snowfall impacts on classified traffic volumes with detailed considerations of trucks and highway types. On the basis of classified traffic volume data from six weigh-in-motion (WIM) sites and weather data from weather stations near the WIM sites located in the province of Alberta, the combined effect of snowfall and temperature on traffic variation for passenger cars and trucks was investigated. Statistically valid regression models with and without the interaction terms were developed to explain the relationship between the dependent variable (the daily truck/passenger car volume) and the independent variables (i.e., the historical average daily volume expected on a normal day in winter, the amount of snow fall, and the average daily temperature on that particular day). The six WIM sites were classified into three distinct groups: regional commuter routes, interregional long distance routes, and special routes. The vehicles were classified into passenger cars and various types of trucks, including single-unit trucks, single-trailer trucks, and multi-trailer trucks. The study results show that the total traffic, passenger car traffic, and truck traffic volumes decrease with the increase in snowfall and severity of the cold for long distance roads like Highway 2. The total traffic and the passenger car traffic decreases as well with severe weather conditions for regional commuter roads like Highway 2A. However, the truck traffic is not significantly influenced by the snowfall and severity of temperature. Interaction models show that the reduction in traffic volume due to cold temperature would intensify with a rise in amount of snowfall for both passenger cars and truck traffic on Highway 2, indicating the existence of cold and snowfall interactions. For Highway 2A, passenger cars experience higher reduction due to the combined effect of snowfall and cold; however, truck traffic is seen to increase during severe weather conditions, which could happen due to shifts of traffic from parallel low standard highways. Another significant finding of this research is that, in general, truck type distribution on commuter routes and main primary highways does not change during the winter season in Alberta. Likely causes for differential effects of severe weather conditions on passenger cars and truck traffic volumes on commuter, long distance, and other types of highways are also described in the thesis. The traffic-weather relationships discovered in this study have numerous applications in the field of traffic monitoring and other types of operational analyses for highways, such as imputation of the missing passenger car, truck, and total traffic data during winter months, which is also described in detail in this thesis.