Research On Stability And Capacity Of Complex Heterogeneous Traffic Flow In Connected Vehicle Environment

With the development of Internet of Vehicles(Io V)and autonomous driving technology,the composition of traffic flow on the road in the future will be gradually complicated.In heterogeneous traffic flow,the conventional vehicles,Adaptive Cruise Control(ACC)vehicles and Cooperative Adaptive Cruise Control(CACC)vehicles have different driving characteristics and reaction times.The direct mixing of ACC vehicles and CACC vehicles into the traffic flow will make the interaction between vehicles in heterogeneous traffic flow more complicated,and will have a greater impact on the macroscopic traffic flow characteristics.Therefore,this paper studies the complex situation in which ACC vehicles and CACC vehicles are directly mixed into the traffic flow.Considering the difference in the reaction time of the vehicles,a car-following model is established for different vehicles.Furthermore,through theoretical analysis and simulation verification,the stability and capacity of complex heterogeneous traffic flow are analyzed.In addition,considering stability and capacity at the same time,the parameters of reaction time and desired time headway are determined.Based on the above parameter values,the simulation experiment of complex heterogeneous traffic flow is designed and the simulation results are analyzed.The main work is as follows:(1)Considering the difference in the reaction time of each vehicle type to changes in the related variables of the front vehicle(speed,speed difference and distance between the front and following vehicle),the car following models of conventional vehicles,ACC vehicles and CACC vehicles were constructed.Based on the framework of the car-following model which considers the reaction time,the linear stability criterion of traffic flow was deduced by the characteristic equation method,and the stability of homogeneous traffic flow was analyzed.At the same time,two kinds of heterogeneous traffic flow stability composed of ACC vehicles and conventional vehicles,and composed of CACC vehicles and conventional vehicles were compared and analyzed.Aiming at the complex heterogeneous traffic flow composed of conventional vehicles,ACC vehicles and CACC vehicles,the stability criterion of complex heterogeneous traffic flow was deduced by the characteristic equation method,and the stability domain was solved.Moreover,numerical simulation verification was carried out,and the stability improvement strategy was discussed through parameter sensitivity analysis.The results show that the high ratio of CACC vehicles can effectively improve the traffic flow stability in complex heterogeneous traffic flow.Specifically,the equilibrium critical ratio of CACC vehicles is 88%,and the equilibrium critical speed value is 30.15 m/s.Compared with conventional vehicles and ACC vehicles,reducing the reaction time of CACC vehicles can improve the stability more significantly.The stability is relatively high when the reaction time term of the CACC vehicles does not exceed 0.2 s.However,when the reaction time term of ACC vehicles is about 0.4 s,only when the proportion of CACC vehicles is more than 89% can keep the traffic flow stable.(2)Considering the difference in reaction time of different types of vehicles,and combining the reaction time with the minimum safe distance,a homogeneous traffic flow capacity model based on critical speed was constructed,and the capacity was compared and analyzed.Furthermore,the fundamental diagram model was used to derive the capacity model of complex heterogeneous traffic flow based on critical speed,and the capacity was analyzed from the theoretical level.In addition,the correctness of the theoretical analysis was verified by numerical simulation,and the capacity improvement strategy was discussed on the basis of parameter sensitivity analysis.The results show that the increase of the proportion of CACC vehicles can effectively improve the capacity in complex heterogeneous traffic flows.The capacity when the CACC vehicles ratio is 90% is about 1.6 times that when the ratio is 0.Compared with conventional vehicles and ACC vehicles,reducing the reaction time of CACC vehicles has a more significant effect on improving the capacity of complex heterogeneous traffic.Specifically,when the reaction time of CACC vehicles is reduced to less than 0.2 s,the capacity can be effectively improved.However,when the reaction time of CACC vehicles is 0.4 s,even a high proportion of CACC vehicles cannot significantly improve the capacity.(3)Considering both stability and capacity,which was equivalent to maximizing capacity under the premise of ensuring stability,the values of some parameters were calculated.According to the reality,the reaction times of conventional vehicles,ACC vehicles and CACC vehicles were determined to be 0.4 s,0.2 s and 0.02 s,respectively.Based on the Non-dominated Sorting Genetic Algorithm-Ⅲ(NSGA-Ⅲ),the Pareto optimal solutions of the desired time headway under different types of vehicles proportions were calculated.Next,a complex heterogeneous traffic flow simulation experiment was designed based on cellular automata.The evolution of acceleration,speed and position was carried out based on the car-following models of the three types of vehicles,and then the simulation results were analyzed from the perspectives of traffic flow safety and vehicle space-time distribution.The results show that when more than 40% of CACC vehicles are mixed into the traffic flow,the reduction ratios of time exposed time-to-collision(TET)and time integrated time-to-collision(TIT)are both greater than 90%,thereby effectively improving the safety of traffic flow.However,when the proportion of CACC vehicles transitions from0 to 10%,the TET and TIT indicators decrease slowly because of the complexity of the traffic flow structure,and CACC vehicles have little effect on improving traffic flow safety.At a density of 40 veh/km,when the proportion of CACC vehicles is more than 70%,traffic congestion and congestion transfer can be effectively reduced.