| The winter weather in Canada, and many parts of the United States, is very severe with extremely cold temperatures, heavy snowfall, blizzards, freezing rain and high wind chills. Such weather conditions cause travel disruptions and frequently necessitate trip adjustments, resulting in significant variations in highway traffic volumes. However, research focusing on the impact of winter weather on highway traffic has been minimal to date, and none of the past studies in the literature considered the effect of severe cold on highway traffic volumes. A detailed investigation was carried out in this study to understand the impact of cold and snow on daily and hourly traffic volume variations with particular consideration given to the highway type and location.;The study results show that the impact of cold and snow on traffic volume varies with the day of the week, the hour of the day, the month of the year, the highway type, and the severity of cold temperature. Traffic volumes decreased with increases in the severity of cold temperatures. During extremely cold weather (below -25°C), the average winter daily traffic volume was reduced by about 30%. Weekend traffic volumes were more susceptible to cold than weekday numbers for all types of highways. Commuter and regional commuter roads experienced the lowest variations with cold. The impact of cold was very high for recreational roads and moderate for rural, long distance roads. Cold temperatures affected traffic volumes more during peak hours than off-peak hours for recreational roads. Commuter roads exhibited the opposite effect, where peak hour reductions were less than off-peak hour reductions. This study also shows a clear indication in the reduction in daily traffic volumes due to snow (reductions between 7% and 17% for each centimetre of snowfall were observed). These reductions can be as high as 51% during severe snowstorms (a snowfall of 30 cm or above). Effect of temperature and snowfall interactions on traffic volume was also investigated in this study.;The traffic-weather models developed in this study have several applications in the field of transportation engineering. Among them, two major applications were selected for detailed analysis: (1) imputation of missing traffic data during winter months and (2) estimation of annual average daily traffic (AADT) from short-term traffic counts undertaken during winter months. The imputation efficiency of the traffic-weather models was compared with the most efficient imputation methods used by highway agencies. The average and 95th percentile estimation errors of traffic-weather models developed here were less than the typical agency methods by about 50%. A new factor approach, incorporating weather conditions, was proposed in this study to estimate AADT from short duration counts taken during winter months. The accuracy of the proposed method is comparable to the traditional factor method. Therefore, the developed traffic-weather models can be recommended to highway agencies to impute missing traffic data and to estimate AADT from short duration counts taken during winter months.;On the basis of traffic volume data from 350 permanent traffic counter sites and weather data from 598 weather stations located in the province of Alberta, the temporal and spatial traffic variations on major road types during different weather conditions were investigated. Regression models were developed to relate traffic volumes under cold and heavy snow conditions with traffic volumes under normal conditions. All the traffic-weather models were statistically significant at 0.001 or higher levels. |
