Study On Adaptation Of Expressway Exit-ramps Under Heterogeneous Traffic Flow Environment

Expressway exit-ramp is an important node to ensure the safe and efficient operation of the road network.According to accident statistics,accidents occurring at the exit-ramp account for more than 40% of the expressway accidents.Once an accident occurs,it will seriously affect the operation efficiency of the expressway.With the continuous development of autonomous driving technology,scholars from various countries generally believe that autonomous vehicles are expected to improve the quality of highway operation.In the future,automated-driving vehicles will gradually infiltrate highways in a certain proportion,forming a heterogeneous traffic flow of a mixture of automated-driving vehicles and manual-driving vehicles.Due to the structural and functional characteristics of expressway exit-ramps,vehicles will have complex behavior of following and changing lanes on exit ramps.Therefore,whether the expressway exit-ramp can adapt to heterogeneous traffic flow and operate safely and efficiently deserves further study.This paper relies on the Shaanxi Provincial Natural Science Foundation Research Project "Study on the Length of Acceleration Lane of Smart Expressways under the Heterogeneous Traffic Flow of Manual-Automatic Vehicles"(2020JM-222)to carry out the research work,taking the expressway exit-ramp under the heterogeneous traffic flow environment as research object.Firstly,on the basis of introducing the definition and classification of the exit-ramp and other road characteristics,conduct a field survey of the exit-ramp,and use video analysis and data statistics technology to analyze traffic flow characteristics such as volume,speed,following,and lane changing.Secondly,based on the driving behavior of automated-driving vehicles and manual-driving vehicles on the exit-ramp,it is determined that the Krauss carfollowing model is used as the longitudinal car-following model for manual-driving vehicles,and the ACC/CACC car-following model is used as the longitudinal car following model for automated-driving vehicles,LC2013 lane changing model is used as horizontal lane changing model for manual-driving vehicles,and the game lane changing model is used as the longitudinal lane changing model for automated-driving vehicles,combining traffic characteristics analysis and domestic and foreign research results,the traffic flow model parameters are determined,and the open source nature of SUMO simulation software is used to construct Heterogeneous traffic flow simulation model.Then,the evaluation indicators of the exit ramp traffic flow parameters are introduced from the macro and micro parameters,select the individual costs that characterize the running quality of the heterogeneous traffic flow on the exit ramp,determine the safety cost,balance cost,control cost,efficiency cost and lane change cost are used as comprehensive cost evaluation indicators,determine the weight coefficients of individual cost.based on the analytic hierarchy process and expert scoring method,and the comprehensive cost evaluation model is constructed.Finally,take the exit ramp the of Weiyang Interchange from Xi’an Ring Expressway to Baomao Expressway as an example,build a basic simulation scenario based on SUMO simulation software and verify the effectiveness of the simulation model,design a simulation experiment,use the length of the exit-ramp deceleration lane and the infiltration ratio of autonomous vehicles as variables to analyze the adaptability of the freeway exit-ramp in a heterogeneous traffic flow environment.The results show that when the deceleration lane length is 215 m,it has better adaptability compared with the current exit ramp deceleration lane length of 180 m without the addition of autonomous vehicles;As the infiltration rate of autonomous vehicles gradually increases,when it is higher than 40%,the heterogeneous traffic flow shows a certain degree of inadaptation under the current road and traffic conditions;Adjust the length of the deceleration lane,when the length is 200 m,the heterogeneous traffic flow has the best adaptability on the exit-ramp.