Urban Road Network Efficiency And Performance Evaluation Based On Macroscopic Fundamental Diagram

As the motor vehicle population increasing,the traffic volume that urban road network needs to support is also increasing.Under the increasing traffic pressure,the efficiency and performance of the urban road network has directly impact on the efficiency of residents' travel and urban operation.The poor operation and low efficiency will affect people's travel efficiency and quality critically.Therefore,it is essential to study the traffic characteristics and overall operational efficiency and performance of the road network to find the cause of the bad condition and propose an effective improving method,which is of great significance for improving the operational efficiency and level of service of road network.Based on Macroscopic Fundamental Diagram(MFD),this paper proposed an evaluation method of urban road network efficiency and performance by developing an evaluation indicator system.By designing simulation experimental road network,the evaluation indicators were applied to evaluate the road network efficiency and performance.The main study contents are as follows:(1)An MFD modeling method for road network efficiency and performance was proposed.The MFD was plotted taking the vehicle density of the road network as horizontal axis and outflow rate of vehicle as vertical axis.The data of MFD was obtained from three typical road networks including grid network,ring network and free network which were established by VISSIM.Then the data of MFD was clustered by GMM,using as the basis for road network efficiency and performance evaluation.(2)Road network capacity evaluation based on MFD.According to the characteristic of MFD,the road network capacity was determined as the vehicle density corresponding to the turning point of stable stage and descent stage of the MFD.Analysis of the capacity of three types of road network suggested that different types of road network has different capacity,and the road network capacity was influenced by the patterns of input volume.(3)Road network operation efficiency evaluation based on MFD.Take the maximum of outflow rate of vehicle,road network capacity,the time when the road network reaches its capacity,and the density and operation time the stable stage of the MFD kept as indicators for evaluating operation efficiency of the road network.The results of the simulation road network indicated that when the total inflow of vehicle remained unchanged,different road networks operate at different efficiency under different patterns of input volume.(4)Road network reliability evaluation based on MFD.Take the operation efficiency,discreteness,stability indices of vehicle density and operation time as indicators for road network reliability evaluating.The changes of the indicators were compared before and after the key links of each type of the road network were invalid.The results illustrated that when the key links were invalid,the reliability indicators of the three typical road networks changed greatly as well as the road network efficiency.(5)Part of the Tianhe District road network were taken as a case,and its road network efficiency and performance were evaluated using the method this paper proposed.The case road network was established by VISSIM and the simulation experiment was carried out.Owning higher road network density and road hierarchy,the efficiency of the case road network was less affected by the key links and the reliability was greater than the three experimental road networks.The road network efficiency and reliability can be improved to a certain extent when the road hierarchy and density increase.This paper proposed an MFD modeling method for road network efficiency and performance evaluation,and based on the road network efficiency and performance evaluation requirements,an evaluation indicator system including road network capacity,operation efficiency and reliability,as well as the corresponding evaluation method were proposed.The method realized the evaluation of the overall efficiency and performance of the road network and could provide a basis for traffic management department to improve efficiency and performance of the road network.