Study On The Macroscopic Fundamental Diagram Estimation Under Heterogeneous Traffic Flow Operation State

With the rapid increase of car ownership in cities,the current traffic congestion is not only limited to road sections or nodes,but evolves from point to line to surface and then to regional traffic congestion problems.In addition,with the development of intelligent transportation and wireless communication technology,the future traffic flow may be a heterogeneous traffic flow composed of Human Vehicles(HV)and Connected and Autonomous Vehicles(CAV).However,there will be a long transition time from HV to fully CAV.The Macroscopic Fundamental Diagram(MFD),which is based on the modeling relationship between the three parameters of average regional traffic flow,average speed,and average density,can better describe the traffic conditions of the road network and facilitate the dynamic modeling of urban traffic at the road network level.At the same time,it can also be used to identify and improve large-scale road network traffic control strategies,which provides a method for solving the macroscopic network traffic congestion.In view of this,this paper studies the macroscopic fundamental diagram of heterogeneous traffic flow operating states consisting of HV and CAV.The main research work is as follows:Firstly,a basic heterogeneous traffic flow model consisting of HV and CAV is constructed.The operational characteristics of the heterogeneous traffic flow are analyzed,and the analytical expressions of the quantitative relationships and their penetration rates of the three types of vehicles,CACC,ACC and manually driven vehicles,are established on the basis of considering the functional degradation of CAV vehicles,which is verified by mathematical and simulation.At the same time,the triangular fundamental diagram(FD)model and cell transmission model(CTM)under heterogeneous traffic flow are also constructed,which can provide the basis for estimating the MFD of urban corridors and road networks.Secondly,based on the Mo C analytical method and considering the functional degradation of CAV,the MFD of heterogeneous traffic flow in urban corridors is obtained by the link basic diagram model of urban corridors,the topology of urban corridors and their signal parameter settings.Using the urban corridor of San Francisco as the study area,an empirical analysis is conducted by Mathematica to compare the MFD of heterogeneous traffic flow under different penetration rates of CAV.As well as comparing the MFD of heterogeneous traffic flows on urban arterials with and without considering the functional degradation of CAV vehicles.The results show that the change of MFD in urban corridors with heterogeneous traffic flow composed of CACC,ACC and artificial vehicles has certain regularity considering the functional degradation of connected and autonomous vehicles.With the increase of CAV penetration rates,the critical density will move backward,so that the density range of the road to maintain the maximum traffic capacity will be long,and the road traffic capacity will also be improved.Considering the functional degradation,the road capacity decreases to some extent,and the congestion density decreases.The MFD obtained by considering CAV functional degradation and not considering CAV functional degradation at low penetration rates is quite different.Finally,by combining a single-loop approximation method with the existing MFD theoretical analysis method,the SA analytical method is used to estimate the MFD of urban grid network considering traffic flow turning.Taking the urban grid network as the research area,the MFD of the network under different vehicle flow turning probabilities is obtained when CAV traffic and manual driving vehicles account for half of the grid network.Meanwhile,to verify the effectiveness of SA analysis,the MFD obtained by the proposed SA analysis method is compared with the MFD obtained from the CTM simulation of the grid road network.The results show that,when the road section is short,the MFD of traditional traffic flow is better than that of heterogeneous traffic flow,and the discreteness is lower.When the turning probability is low,the MFD estimated by CTM simulation of heterogeneous traffic flow is in good agreement with the MFD estimated by SA.When the road section is longer,the MFD of heterogeneous traffic flow is better than that of traditional traffic flow,and the discreteness is lower.With the increase of turning probability,the MFD estimated by heterogeneous traffic flow CTM simulation is in good agreement with that estimated by SA.