Research On Signal Priority Control Strategy Of Emergency Vehicle Under Connected And Automated Vehicle Environment

With the deepening of urbanization,traffic congestion has become a common problem in many cities.In the complex traffic environment,the obstacles encountered by emergency vehicles on their way to the rescue site have also gradually increased,resulting in a large increase in the travel time of emergency vehicles,and the consequences of not timely rescue will be impossible to predict.Therefore,how to ensure the priority passage of emergency vehicles in urban intersections by traffic control system has become an urgent problem to be solved.In recent years,due to the continuous improvement of connected and autonomous vehicular technology,the traditional traffic control system is undergoing a transformation.And connected and autonomous vehicular technology provides a new method for ensuring the priority passage of emergency vehicles.Therefore,this paper study the signal priority strategy of emergency vehicles by connected and autonomous vehicular technology,and divides the signal control for emergency vehicles into the signal priority part before the emergency vehicle passes the intersection and the traffic signal recovery after the emergency vehicle passes through the intersection part of the signal transition.This paper first analyzes the research status of priority part and transition part of emergency vehicle signal,which an Introduction of the connected and autonomous vehicular transportation system is given,and the key technologies of the connected and autonomous vehicular application in the coordinated signal control are analyzed.The main research contents and main ideas of this paper are determined according to the situation that emergency vehicles may encounter when running and the actual traffic demand after emergency vehicles pass the intersection.Secondly,based on the real-time information interaction between vehicle mounted unit and roadside unit in the connected and autonomous vehicular environment,a two-stage model of "emergency green wave" was established according to the operation status of emergency vehicles and road traffic status received by roadside unit to ensure the unblocked flow of emergency vehicles on the rescue way.In the first stage,the timing parameters of signal control at each intersection on the route of emergency vehicles were optimized,and the "emergency green wave" phase difference model was constructed to minimize the delay of all vehicles on the emergency vehicle route,so that all the queuing vehicles in front of emergency vehicles could be evacuated as soon as possible,and the emergency vehicles could reach the location of emergency events as soon as possible.In the second stage,according to the actual emergency vehicles reach the intersection when the signal phase,compare the emergency vehicle arrived in time,at the end and emergency vehicles in front of the queue dissipation phase completion time relationship between the front and back,then select the corresponding signal control methods,such as green light extension,red light off early,for emergency vehicles priority for double security.Thirdly,after the emergency vehicle passes the intersection,social vehicles will be affected by the priority of emergency vehicle signals,especially for social vehicles on the intersecting roads on the route of emergency vehicles,which will have a large delay time.Therefore,this paper proposes a signal transition model for the coordinated signal recovery process after emergency vehicles pass through,establishes a signal transition model according to the queue lengths of different entrances,and solves it by an improved particle swarm algorithm.It can better meet the traffic needs of emergency vehicles after priority passage,establish a good start for the coordinated control scheme after recovery,so as to ensure the control effect of coordinated signals after recovery on traffic flow.Finally,simulation experiments are carried out on the two-stage model of "emergency green wave" and signal transition model respectively,and the traffic data of some sections of Xinghu Street in Suzhou is taken as an example to verify the feasibility and effectiveness of the model.In terms of emergency signal priority,compared with the simulation results of single-point signal priority control of emergency vehicles,the proposed priority control strategy reduces the average delay time of emergency vehicle and the delay time of uncoordinated social vehicle by28.8% and 14.62%,respectively.In terms of signal transition,compared with the simulation results of immediate transition and smooth transition,the signal transition scheme proposed in this paper reduces the average delay time of social vehicles by29.07% and 22.47% respectively,which can better meet the traffic demand in the process of restoring priority signal of emergency vehicles to the original coordinated signal scheme.In this paper,according to the actual traffic demand of emergency vehicles before and after crossing the intersection,modeling and solving the intersection signal timing scheme are respectively carried out,which is of certain significance to realize the priority of emergency vehicles in the connected and autonomous vehicular environment.