Study On Safe Spacing Of Expressway Tunnel And Interchange

With the acceleration of expressway construction in China,the proportion of tunnels and interchanges is gradually rising in the expressway construction.Accordingly,there are many tunnels and interchanges with short spacing.It's easy to cause traffic accidents and traffic congestion,and has a adverse impact on the operation efficiency and safety of expressway.Therefore,with the help of the lane change theory and traffic conflict technology,this paper studies the safe spacing of expressway tunnel and interchange from two aspects of theoretical calculation and microscopic simulation.Firstly,the spacing of expressway tunnel and interchange is defined.It is clear that the spacing is composed of net spacing and length of speed change lane.The direction from tunnel entrance to interchange ramp with relatively more potential safety hazards is determined as the research object.The main factors affecting the spacing of tunnel and interchange are traffic flow,vehicle speed,traffic flow characteristics,vehicle composition,driver's visual characteristics,driver's response characteristics,setting of traffic indication signs and the number of the lane.Then,considering the influence factors and the most unfavorable driving conditions,the calculation model is established for each stage of the lane change process based on the lane change theory.And the recommended safe net spacing values under different combination of design speeds and lanes are obtained.Afterward,based on traffic conflict technique,the simulation model is established by VISSIM and the traffic conflict rate is selected as the evaluation index of integral traffic conflict severity.The minimum safe net spacing of different design speeds and lanes under general terrain conditions and restricted terrain conditions is obtained by using iterative clustering analysis and fuzzy evaluation method.Then,by comparing the results of the two methods,the recommended minimum safe net spacing values under general terrain conditions and restricted terrain conditions of tunnel and interchange with different design speed and lane are determined.Finally,the paper puts forward the traffic safety safeguard measures for short-distance expressway and tunnel.The research methods and conclusions of this paper provide reference for scholars,road engineers and existing norms that study on short-spacing tunnels and interchange,and have a certain practical significance.