Determination Of Vehicle Trajectory And Its Dangerous Sections For Low-Grade Mountain Highway Curves

China has a vast number of mountain areas,and terrain is complex and diverse.In order to meet the daily travelling needs of mountain residents and the needs of tourism development,a large number of low-grade mountain highways have been constructed in China.Curve,one of the main alignment of low-grade mountain highway,belongs to the traffic accident-prone section of highways because of the particularity of their alignment condition and the complexity of their driving environment.The main traffic accidents have frontal collision and side collision,and the most accidents occur because the actual vehicle trajectory is inconsistent with the desired trajectory that depends on road alignment design.Typically the inconsistence would result in the travelling vehicle crossing the highway centerline and even intersecting with the opposite vehicle.Therefore,it is necessary to study the vehicle trajectory and dangerous areas for low-grade mountain highway curves.Firstly,the twelve highway curves from Ebi Village to Guling Scenic Spot in Huanxi Town,Fuzhou City have been chosen as test sites.Vehicle velocity,curve radius,total curve length,transition curve length,longitudinal gradient,superelevation and subgrade widening are considered as the primary influencing factors of vehicle trajectory.In this paper,vehicle trajectory and velocity index are obtained based UAV videos.Plane linear equilibrium index,longitudinal gradient index,transverse slope index and subgrade widening index are calculated based on their corresponding influencing factor.Secondly,the distribution map of the vehicle trajectory-section position and the general trajectory trend map of each curve are drawn according to vehicle trajectory and each influence index.The trajectory’s general law,distribution law and change law of each curve are analyzed,and the influence of each index on vehicle trajectory is analyzed as well.Subsequently,velocity variation across the curve,the variation of vehicle trajectory with the speed and the variation of vehicle trajectory with plane alignment are studied.Moreover,it is found the influence of each index on vehicle trajectory is significant.A three-dimensional relationship model of section position–velocity-trajectory value is established.Thirdly,the potential dangerous section length,the potential dangerous section area,the conflict dangerous section length and the conflict dangerous section area can be calculated depending on general trend of vehicle trajectory at different velocity ranges.The distribution property of the dangerous area length and area at road curves have been analyzed.Finally,the entropy method is used to calculate the weight of each influence index about dangerous sections.Based on the calculated weight of each influence index,the comprehensive influence index of dangerous sections of curves is constructed.Subsequently,a model for predicting the length and area of potential dangerous sections is established.As a result,the speed limit for each curve is proposed based on the prediction model.