Simulation Study On Traffic Flow Of Expressway Ramp System Under Accident Conditions

With the construction and development of expressway infrastructure,the traffic volume of expressway is increasing,so serious consequence will occur after traffic accidents on expressways.In the section where there is an entrance ramp on the expressway,due to the existence of the entrance ramp,the main line traffic will be disturbed.In addition,after the traffic accident happen on the section,the combined effect of the ramp and the accident will occur.Therefore,the paper studies the traffic flow of expressway ramp system under accident conditions.Considering the traffic flow characteristics of the expressway ramp system,a one-way two-lane CA model of the highway with ramps was established.Traffic accidents were introduced and the lane changing rules of the accident sections were defined.Analyze the impact of different parameters such as the duration of the accident,the length of the accident area,and the location of the accident on the ramp system.Finally,traffic control is adopted for the ramp system under the accident.The main work of the paper is as follows:(1)Starting from the basic three-phase traffic flow KKW model,the existing KKW model is improved considering the driver sensitivity and the different deceleration ranges within the synchronization range.(2)Based on the improved KKW model,a one-way two-lane cellular automaton model is established by using symmetric lane changing rules.Meanwhile,the vehicle rules of entering ramp are defined and the traffic flow cellular automaton model of the expressway ramp system is constructed.Considering the change of the main line and the ramp entrance probability,the influence relationship between the ramp and the main line traffic flow is obtained by analyzing the parameters such as flow,speed,road occupancy rate and average lane change rate.The result is that as the probability of entering the main line increases,the ramp system flow value will increase to a maximum of 1.5 veh/s,then quickly decrease and remain stable at 1.2 veh/s.(3)In the highway ramp system model,defining the rules for the occurrence of traffic accidents,the main line segments is divided into normal road sections,merging segment,diversion segment,and buffer segment where the lane change priority of the vehicle is determined according to the vehicle position and speed relationship.Considering the different durations of accidents,the length of different accident areas,and the change of accident location,the traffic flow variation law of expressway ramp system under the influence of accidents is obtained by analyzing the road time and space diagram,flow rate and speed change diagram.(4)When the accident occurs downstream of the entrance ramp,the coordinated control strategy of the main line variable speed limit and the entrance ramp feedback control is adopted for the expressway ramp system,the simulation is carried out.By comparing and analyzing the flow,speed and space-time diagram obtained by the control measures and the non-control measures,the results show that the control strategy can reduce the spread range of the road congestion zone under the accident conditions,increasing the saturation flow of the ramp system and the corresponding average lane speed under the saturated flow,which reduce the impact of traffic accidents on traffic flow and provide reference for traffic control of expressway ramp systems under accident conditions.