Modeling And Analysis Of Mixed Traffic Flow In Connected Automated Vehicle Environment Based On Cell Transmission Model

Faced with the huge number of motor vehicles,the increasingly serious traffic congestion has become a difficulty and pain point for major cities at home and abroad.Nowadays,the domestic and foreign vigorously promote the connected automated vehicles and invest in the research and development of related industries,ushering in the golden development period of connected automated vehicle technology,which brings new methods to the contradictions and difficulties existing in the traditional road traffic.However,the popularization of connected automated vehicles needs a transition period,not overnight.Therefore,the mixed traffic flow of different vehicle types on the road is an inevitable trend of traffic development.The current research on mixed traffic flow mainly focuses on the micro-level,while at the same time the car-following degradation of connected automated vehicles is considered and related research based on the meso-level analysis of the mixed traffic flow characteristics remains to be explored.Therefore,this paper takes the mixed traffic flow composed of human-driven vehicles and connected automated vehicles as the research object,constructs the Cell Transmission Model(CTM)of mixed traffic flow based on the fundamental diagram of mixed traffic flow,and then analyzes the characteristics of mixed traffic flow from a mesoscopic point of view.The specific research contents are as follows:(1)The fundamental diagram of mixed traffic flow has been established.For the car following degradation phenomenon of connected automated vehicles,a mathematical formula is used to describe the mixed traffic flow under different penetration rates,and Newell,ACC,and CACC models are used to simulate the car following behavior of human-driven vehicles,adaptive cruise control(ACC)and cooperative adaptive cruise control(CACC)vehicles respectively.On this basis,Section 3.3 derives the flow-density fundamental diagram of homogeneous traffic flow and mixed traffic flow based on the relationship between headway spacing and density in the equilibrium state,which lays the foundation for the later model construction.Besides,the fundamental diagram is verified by simulation experiments.The results show that the flow-density scatter distribution is consistent with the theoretical fundamental diagram curve,which proves that the fundamental diagram of mixed traffic flow is effective and feasible.(2)The CTM model of mixed traffic flow with different penetration rates has been constructed.Firstly,based on the fundamental diagram of mixed traffic flow,the parameters of the CTM model of mixed traffic flow with different fundamental diagrams are extracted,including maximum capacity,congestion density,and backward wave speed.Secondly,according to the principle of the classical CTM model,the mixed traffic flow CTM model is constructed in Section 4.2,which includes the basic road section,diversion node,and merge node.Finally,two simulation methods,CTM simulation of mixed traffic flow and microsimulation based on a car-following model,are used to compare and verify the simulation results under different penetration rates.The results show that: the two simulation methods of density heatmaps are consistent,the error value at the end of congestion is not more than 47 s,the relative error is not more than 5.91%.Therefore,the results prove the effectiveness of the mixed traffic flow CTM model.(3)The congestion characteristics of mixed traffic flow under the moving bottleneck on the expressway have been analyzed.Taking the moving bottleneck on the expressway as an example,the CTM model of mixed traffic flow is applied to the traffic scene of the moving bottleneck.And then,in Section 5.2,the congestion characteristics of mixed traffic flow are analyzed by using the average travel speed,congestion delay,and congestion scale.The results show that the congestion degree of mixed traffic flow is greatly alleviated under a high penetration rate,especially when the penetration rate is 1.What’s more,the sensitivity analysis shows that the traffic demand of the main highway and the duration of the bottleneck is positively correlated with the degree of congestion,while the results of congestion assessment under different model parameters are slightly different,but the impact is small.The above research results contribute to the analysis of the operation characteristics of mixed traffic flow in the environment of connected automated vehicles,further promote the high efficiency,intelligence,and informatization of road traffic management and control,which provides a theoretical reference value for the future connected automated vehicles in the actual road traffic management and control.