A Study on the Ultimate Velocity for Vehicles Going through Roadway Curves to Avert Sideslip

The part results of a study on the factors influencing safety as driving a vehicle at road curve are reported in this paper. A motivation doing this research is to reduce casualties in traffic road accidents since many accidents happened at road curve sections. An improved mathematical model is constructed based on the mechanical analysis of vehicle motion. In the model, excepting the factor of road surface superelevation angle, the effects of longitudinal gradient of road curve and wind force are also taken into consideration. Two typical road curves respectively in two existing roadways in Nagano Prefecture, Japan are selected as the investigated road curves, which include the road curve section where a bus traffic accident well known has occurred. Four types of vehicles including bus are taken as the studied objects. The relationship between the ultimate velocity for vehicle to travel bending a road curve and to safely avert sideslip and relative parameters is built. The predicted results are given and discussed. The results show that the ultimate velocity as one of the important parameters to avert bus accident decreases with wind speed increasing. With the curve radius increasing, the ultimate velocity increases in all road surface conditions, in which the ultimate velocity for bus traveling on dry road surface increases most quickly, then on wet road surface, snow accumulation road surface and frozen road surface successively for ranges of velocity limited to 110 km/h and a curve radius to 350 m. For same wind speed, the bigger the longitudinal gradient ?, the smaller the ultimate velocity.