Research On The Cooperative Merging Control Strategy Under Connected And Automated Vehicle Environment

The merging segment of urban freeway is an important node in city road system.Traffic jam and traffic accidents often occur due to vehicles’ mandatory lateral conflicts.At present,existing control methods are popular due to their works well in optimizing traffic conditions.However,the timing of merging human-driven vehicles(HVs)is still determined by the driver.Different drivers have different choices when facing the gaps.It may result in the mainline gaps can not be fully utilized by on-ramp vehicles,which could lead to traffic flow breakdown and vehicle delay.In addition,it is difficult for drivers of HV to judge the motives of other drivers when they merging into mainline.So in this case,the traffic efficiency reduced,the risk of collision increased.Connected and Automated Vehicles(CAVs)can obtain real-time operational data of adjacent vehicles,including speed,acceleration and surrounding environment information.Besides,under the premise of ensuring safety,traffic managers can control individual vehicle trajectory based on the prediction of time when the mainline and on-ramp vehicles arrive at the merging point to improve the traffic efficiency of the merging area.This paper studied the urban merging areas under the CAV environment,the main work of this study is showed as follows:1.Based on the analysis of HV driving behavior characteristics,a merging control method in CAV environment was proposed.By obtaining information of vehicles from roadside control unit,time prediction of mainline and on-ramp vehicles arriving at the merging point,generation of mainline vehicle lane changing scheme and optimization of on-ramp vehicle speed were realized.2.Traffic capacity is an important parameter in evaluation system of city road.Capacity of ramp-way junction is an important basis for analyzing the operation status of traffic flow in merging area and formulating control measures.Based on the Cowan M3 distribution and the gap acceptance theory,this article deduced the calculation formula of ramp-way junction capacity in two control methods.The calculation results of three main lanes and single onramp lane under different mainline traffic demand were taken as basic examples.The influence of relevant parameters,such as critical headway,critical merging gap,number of mainline lanes,on the capacity of way-ramp junction and the throughput of merging area was analyzed.3.Because CAVs is not mature,the conditions of real vehicle experiment that can’t be carried out for many times.Therefore,VISSIM was selected as the simulation software to establish three merging environments: HVs,automated vehicles(AVs)without cooperative lane changing control and CAVs under cooperative lane changing control.The throughput of merging area and the average travel time of vehicles were selected as the evaluation indexes.Simulation results verified the accuracy of the capacity calculation model and the effectiveness of the cooperative lane changing control method for improving the operation efficiency of merging area.This paper selected the south on-ramp of Nanhu square on the Changchun Western expressway as research site,analyzed meging characteristics of HVs,put forward a merging control method of CAVs consider cooperative lane changing behavior.Several simulations were carried out on the vehicle operation conditions in merging area under different mainline and on-ramp traffic demands.It is proved that the improved control method can increase throughput of merging area and reduce average travel time.Under the same traffic demand,the average travel time of CAVs with cooperative control method is significantly less than that of HVs,which is about 14% lower than that of AVs without cooperative control.