Research On The Vertical Design Of Road Crossings And The Adaptability Of Vehicles In Mountainous Cities

As the distribution center of urban roads,level intersections have a decisive influence on the operation of urban traffic.According to a large number of domestic and foreign statistics,road traffic accidents that occur at intersections account for 60% of the total number of accidents,and the proportion of accidents that occur at level intersections in mountainous cities is even higher.At present,when designing mountain city level intersections,due to factors such as urban planning and topographic constraints,two roads with excessively large longitudinal slopes often intersect,which will lead to reverse slopes and transverse slopes at the corners of the level intersection.The phenomenon of "ups and downs" and "wobbles" appear where changes are too fast.Although the traffic control department will use safety measures such as the installation of signal lights,speed limits at intersections,and installation of speed bumps to alleviate hidden dangers,the effect of improvement measures is not obvious due to inherent defects in the road design.Therefore,it is very urgent and necessary to start from the defects of the road itself,solve the hidden design hazards,and ensure the safety and comfort of driving at intersections.This paper first conducts an on-site investigation and analysis on the intersections of typical large longitudinal slope roads in the urban area of Chongqing,and concludes that there are three shortcomings in the vertical design of urban road intersections in Chongqing: the design range of the intersection is too small,which leads to the length of the vertical curve.Unreasonable setting of the sum radius will cause the phenomenon of "bulge" and "sag";the length of the cross-slope transition section within the intersection is too short,which leads to the phenomenon of "wobbles" when the cross-slope changes too fast and the gradation rate is too large.The unreasonable setting of the cross slope of the road at the intersection may cause reverse superelevation at the turning curb,resulting in the danger of turning vehicles overturning and overturning.Then,theoretically analyze the vehicle trajectory,turning radius,trajectory width and super-elevated cross-slope at the level intersection.Based on the analysis results,these elements are discussed in relation to the vehicle’s driving adaptability in the vertical design of the level intersection.contact.Finally,two improvement measures are proposed:The first is to make the cross slope of the right-turn lane independent of other lanes by setting up a traffic island,and the super-elevation at the right-turn lane can be set reasonably to avoid the reverse slope at the turn.The second is to disperse the traffic adaptability problems in the intersection range to the roads on both sides.By expanding the design range of the intersection,set the super-elevation gradient section outside the intersection to increase the elevation value at the center of the intersection..At the same time,the mathematical relationship between the elevation value of the intersection center point,the cross slope of the road arch and the length of the unilateral elevation section is deduced,which provides a theoretical reference for the designer to select the optimal parameters reasonably.Finally,the vertical design traffic adaptability optimization project at the intersection of F3 road and branch road 1 in Caijia New District of Chongqing Liangjiang River was used as an engineering example to verify the optimization effects of the two measures.In addition,Carsim simulation software was used to carry out simulation experiments,and four indexes affecting vehicle operation stability were put forward,namely,vertical wheel load,body roll angle,lateral acceleration,and yaw rate.By comparing and analyzing the changes of these four indexes,it can be seen that the vertical intersection of the plane The driving adaptability of the designed vehicle has been significantly improved,which proves the feasibility and effectiveness of the two optimization measures.The research results provide new ideas for designers to choose different optimization schemes according to the terrain conditions of intersections in actual production,and also have certain theoretical significance for perfecting the research of vehicle driving adaptability in the vertical design of level intersections.