Study The Key Technical Indicators Of Major Forks And Branching Connections Of Freeway

China’s freeway network,which is generally matured at present,has laid a solid foundation for national road transportation and transport efficiency.With the continuous growth of network density,traffic volume,regional and sectional network traffic complexity,the freeway major forks and branch connections and system interchange are emerging.However,relevant regulations and norms,together with researches,have less referred and of limited practicality to major forks and branch connections.The major forks and branch connections are important nodes for the road network’s overall and sectional traffic safety and efficiency,and it is of great significance to study their key technical specifications.Based on analysis and relevant data,this paper has reviewed research status of major forks and branch connections at home and abroad;summarized characteristics and functions of major forks and branch connections;proposed their functions in the regional road network and in the nodes;identified models of major forks and branch connections as well as different traffic components,differences and similarities of major forks and branch connections between those of interchanges’;defined application conditions of different major forks and branch connections models;and enriched relevant regulations and norms.In more detailed aspects,based on analysis of traffic features of the major forks and branch connections as well as existing basic recognition sight distance models,this paper has provided a calculation model for the recognition sight distance in major forks and branch connections and suggested indexes for various conditions.Furthermore,combined with vehicle confluence safety and actual needs of the traffic flow in the confluence area,this paper has brought up concept and models of safety sight distance for branch connections.After calculation and consulting safety sight distance,the geometrical dimensions of the visibility triangle for sight distance ranges under different needs are provided to branch connections.According to different types of sight distance value provided by calculation,the horizontal circular curve and the vertical curve radius of the major forks and branch connections are deduced to meet different types of sight distance value.Furthermore,based on the characteristics of the traffic flow at the front of the major forks and drivers’ physiological characteristics,a calculation model of the required length of the major forks for the smooth running and safely shunting of the vehicle is proposed.The front of major forks is divided into three basic calculation units.Calculation methods are provided in different combinations of unit types and unit length according to different situations.And combinations types under general or restricted conditions are provided considering actual vehicle operation status.According to the calculated length,different spacing values between major forks and constructed facilities are provided regarding different bifurcation types and numbers of lines.To complete unit types,post distance needed for the tunnel outlet is calculated and basic unit for the spacing calculation of major forks and tunnel outlet is provided according to characteristics of traffic flow at the tunnel outlet and of the drivers.By analyzing characteristics of shunt position of freeways,time and space distribution and statistical features of traffic accidents,the paper puts forward a method to quantify the braking trajectory as an index to evaluate the safety of vehicles running in freeway major forks and dynamic evaluation procedure for freeway bifurcation point safety.According to the research conclusion,attention should be paid to the road sign setting and safeguard implementing works at major forks.