Optimized Geometric Design of Mountain Highways based on a Vehicle-Road Coordination Model

Due to limitations of topography and other conditions, the curve sections of mountain highways are always prone to accidents. In order to improve the safety level of mountainous highways, this paper proposes an optimize geometry design method of mountain highways by comprehensively considering the roles of vehicle and highway. Based on mechanical analysis of vehicle driving on curve sections, the force characteristics of sideslip and rollover for critical state of lateral instability is calculated, so as to establish a vehicle-road coordination safety model. By theoretically analyzing the relationship between highway design parameters (the minimum curve radius, super-elevation and the lateral adhesion coefficient) and driving speed, the critical safe speed is determined. Vehicle sideslip and rollover accidents are simulated via CarSim software, the critical safe speed and the safe model are verified. Model analysis and simulation results show that when the design speed exceeds 60 km/h, the specification of minimum radius is conservative. For high grade mountain highways with high design speed, traffic safety should focus on speed limiting, so the minimum curve radius can be reduced according to the calculations of the safety model and simulation results of the CarSim software. For low grade highways, the minimum radius should be increased to improve the safety level. For mountain highways with lateral adhesion coefficient less than 0.15 in a special environment, the minimum radius and super-elevation should be checked during design.