Research On Congestion Pricing Control Based On Macroscopic Fundamental Diagram

Traffic congestion is a hot topic in urban issues.The limited space resources of cities cannot meet people’s increasing travel needs.Therefore,traffic demand management is particularly important.The law of traffic flow is an important basis for macro-control.In recent years,the macroscopic fundamental diagram of traffic flow(MFD)has been widely used in macro-control and traffic status evaluation of road network.This model focuses on the relationship and nature of network traffic parameters(weighted average flow,average density and average speed),and the relationship between inflow and outflow of network.The MFD can monitor traffic status of road network in a wide range and for a short time,and it can provide reliable decision-making basis for pricing research on regional traffic congestion charges.Firstly,this paper defines total number of vehicle kilometers from perspective of traffic benefit,which describes the capacity of road network,and expands the two-dimensional macroscopic fundamental diagram(MFD)into a three-dimensional generalized macroscopic fundamental diagram(GMFD).It is found that average speed is a nonlinear function of average density and standard deviation of density on network level.Based on this,volume delay function of the link in BPR(Bureau of Public Roads)form is extended to the whole network,and the standard deviation of the density is incorporated into this model variables,then the traveled speed function of network is established,which can describes network traffic law.The function is calibrated by statistical method and theoretical derivation method.Data of Taidong business district in Qingdao is used for test,and it is found that traveled speed function of network considering the standard deviation of density is more in line with the physical variation of actual traffic.Then,a regional congestion pricing model is established with combination of MFD theory and multi-agent simulator(MATSim).From view of fairness and reliability,the road network capacity(that is critical density for macro-control)is obtained through MFD,and the proportional controller is set to adjust pricing plan,then the multi-agent simulator obtains the MFD shape after pricing implementing.The best-shaped MFD corresponds to the best pricing plan.This paper demarcates the Taidong business district of Qingdao as cordon.Through the results of simulation,it prove this pricing model reliable.It is found that the best pricing plan not only eliminates the delay time of travelers in road network,but also shortens the length of congestion peak time.In addition,the cost savings of actual trips and delays of plan are much higher than total costs paid,which contributes to achieve User Equilibrium(UE).The spatial-temporal characteristics of road network capacity is hold by the MFD,which is obtained from traffic big data,and it is a promising method to determine pricing standard for congestion pricing by MFD theory.This paper can provide reference for the implementation and evaluation on congestion pricing policies for urban road networks.