Traction Performance of Transit and Paratransit Vehicles in Winter

The traction performance of transit and paratransit vehicles during the winter is an important factor in public transportation system operations. Vehicle traction forces are significantly reduced on snowy or icy surfaces, specifically during stopping, starting, cornering, and hill climbing. Reduced traction increases stopping distances and decreases controllability when a vehicle stops in an emergency situation. This study evaluated the traction performance of transit and paratransit vehicles on snowy and icy surfaces. Field tests were conducted in Fairbanks, Alaska, using three types of vehicles—a 41-passenger transit bus, a 32-passenger transit bus, and a 9-passenger paratransit vehicle. Each vehicle was tested for different combinations of tire types, including highway tires, snow tires, studded-siped tires, highway three-rib tires, all-season tires, and snow-siped tires. Tests of winter traction performance evaluated stopping distance, starting traction, hill climbing, cornering, and controllability. For similar tire combinations and surface conditions, the tested transit and paratransit vehicles had different traction performance. Results indicate that winter traction performance is significantly influenced by vehicle type, tire combination, and road surface (compacted snow or ice). Research findings and recommendations for tire combinations best suited for winter traction are presented.