Study On The Critical Characteristics Of Mixed Traffic Flow Of Manual And Autonomous Driving On Expressway

Expressway traffic is the research hotspot of traffic flow,and the intervention of autonomous vehicles is bound to have an impact on expressway traffic flow.Based on the research of basic traffic flow theory,this paper formulates the rules of manual-automatic driving mixed traffic flow model under the framework of three-phase traffic flow theory,analyzes the phase transition effect of automatic vehicles on expressway traffic flow by simulation,and studies the congestion phase transition mechanism of mixed traffic flow.The research is as follows:(1)In this paper,taking into account the slow-start behavior of the vehicle and the fact that it is more difficult for a driver keeps a particular driving state for a long time to respond to external stimuli timely,the speed disturbance rules of the classic model are improved,and a manual driving vehicle model is proposed.Considering that the speed adaptation process of an autonomous vehicle should not be determined by a fixed expected time distance,but should be divided into sections,we analyzed the two major influencing factors of the expected time distance and the relative speed difference,and then proposed an autonomous vehicle model.On the basis of the above analysis and modeling,a mixed traffic flow model of manual driving vehicle and automatic driving vehicle under the frame of three-phase traffic flow is proposed,hereinafter referred to as the TMA model.The stationary solution of the model conforms to the basic assumptions of the three-phase traffic flow theory,so the model can simulate the three-phase state and its basic first-order phase transition phenomenon.(2)Based on the above-mentioned TMA model,we carried out the simulation under single lane condition and the phase transition phenomenon of mixed traffic flow from free flow to congested flow under the influence of speed self-disturbance is captured.The results show that with the increase of the proportion of automatic vehicles,both the traffic flow rate(veh/h)and the average speed(km/h)corresponding to F?S process shows an upward trend.Besides,from the characteristics of the first-order phase change of traffic flow,it can be seen that the intervention of automatic vehicles can effectively improve the stability of expressway traffic flow.Then,considering the different driving modes of autonomous vehicles,we further divide the autonomous vehicles into two types: comfortable and high-speed.The two-lane TMA model focuses on distinguishing the characteristics of lane changing behavior of the two types of autonomous vehicles.Lane changing rules and lane changing probability.It can be seen from the simulation results that both types of autonomous vehicles effectively increase the average flow of traffic flow and reduce the risk of traffic collapse and the intensity of phase transitions.However,due to the impact of non-active lane changingbehavior of comfortable autonomous vehicles,the traffic flow and speed are relatively low when the vehicle composition conditions are the same.High-speed self-driving vehicles can promote the convergence of traffic flow speeds,and there is a tendency to promote the generation of ideal synchronous flows,but the lane changing frequency is much higher than that of comfortable self-driving vehicles,which may reduce the passenger experience.