Study On Safety Optimization Of Vertical Designof Road Intersection In Mountain City

When designing plane intersection of mountain city road,the elevation of main control points in the intersection area is limited by urban planning,surrounding ground and other factors,which often leads to the situation that the longitudinal slope of two intersecting roads is too large in the intersection area,which leads to the adverse factors such as reverse superelevation and cross slope gradient too fast in the vertical design of intersection.In order to improve its traffic safety,traffic management measures such as speed limit at intersections and setting deceleration belts are usually adopted,but these measures do not solve the defects of intersections themselves,and at the same time reduce the efficiency of intersections.Therefore,from the point of view of active control,it is necessary to optimize the vertical design of intersections in order to reduce the impact of adverse factors on traffic safety.Firstly,through field investigation on the plane intersection of Chongqing urban road with large longitudinal slope,the problems and causes of the vertical design safety of the intersection are analyzed.It is found that the insufficient length of the transition section of the cross slope will cause "twists and turns" in the intersection area and reduce the driving comfort;The longitudinal slope of the intersecting road leads to the serious phenomenon of the reverse superelevation of the road in the process of turning,and there is a risk of overturning.Secondly,on the basis of summarizing the vertical design theory of intersections,combined with the analysis of human,vehicle,road and environment,the factors affecting the vertical design safety of urban road intersections in mountainous areas are put forward,including vertical curve,longitudinal slope,transverse slope and length of gradient section of transverse slope.Then,the idea of safety optimization for vertical design of intersections is put forward,that is,by increasing the elevation value of intersections central points,expanding the design scope of intersections and setting extra-high sections outside the intersections,the purpose of reducing reverse superelevation and decreasing the gradient of cross slopes is achieved,and the concrete implementation steps of optimization are given in theory.Aiming at the safety optimization of the vertical design of the intersection of urban trunk road and sub-trunk road,a table of recommended values of the arch cross slope and the length of one-sided elevation section ofsuperhighway is put forward,and the traffic safety before and after optimization is compared.Finally,relying on the safety optimization project of the vertical design of the intersection of Hengyi Road and Heyuan Road in Chongqing,the calculation process and implementation steps of the safety optimization microprocessing measures for the vertical design of the intersection are given.The trucksim vehicle dynamic simulation software is used to proceed from the following aspects: trajectory error,body roll angle,wheel vertical load,lateral acceleration,yaw angular velocity and longitudinal acceleration.The results show that the "twist" phenomenon of Hengyi road disappears after optimization,the reverse superelevation of right-turning road decreases by 0.88%,the optimization rate of stability parameters is 18%~24%,the reverse superelevation of right-turning road of Heyuan road decreases by 0.68%,and the optimization rate of stability parameters is 10%~14%.The research results have certain theoretical significance for improving the safety optimization method of vertical design of intersections,and can provide some reference and reference for the design of plane intersections on large longitudinal slope sections of Mountain Urban roads.