A Two-layer Network Dynamic Congestion Pricing Based On Macroscopic Fundamental Diagram

As urban traffic congestion worsens,dynamic congestion pricing has attracted increasing attentions during the recent years.Nevertheless,limited research has been conducted to address the dynamic tolling scheme at the network level,such as to cooperatively manage two alternative networks with heterogeneous properties,e.g.the two-layer networks consisting of both expressway and arterial network in the urban areas.Recently,the macroscopic fundamental diagram(MFD)developed by both field experiments for the taxi data in downtown Yokohama in Japan and simulation tests for the San Francisco Business district in Carlifornia illustrates a unimodal low-scatter relationship between the mean flow and density network widely,providing the network traffic state is roughly homogeneous.It reveals traffic flow properties at an aggregated level and sheds light on dynamic traffic management of a large network.This paper proposes a bi-level programming toll model,incorporating MFD to solve the unbalanced flow distribution problem within the two-layer transportation networks.The upper-level model aims at minimizing the total travel time,while the lower level focuses on the MFD-based traffic assignment,which extends the link-based traffic assignment to network wide level.Genetic algorithm(GA)and the method of successive average were adopted for solving the proposed model.An online experimental platform was established using VISSIM,MATLAB,and Visual Studio software packages.Finally,from Paris,France,China,Chengdu and other areas of the city ring road network structure,an abstract two-layer network consisting of the peripheral ring expressway network and center grid arterial network is constructed.Through the building simulation platform,the dynamic congestion pricing model based on MFD is evaluated.During the simulation,the real-time traffic flow status data of the road network is collected and transmitted to the model solution software.After the calculation of the program,the real-time predicted congestion charge value is fed back to the simulation software.The users select the travel path in real time according to the total travel cost,so as to achieve the purpose of adjusting the traffic demand distribution in the road network timely.The simulation example illustrates that using the proposed network dynamic charge policy,a significant reduction in the total travel time is achieved and the value of total charging toll is less than the value of total travel time savings.By comparing the network running status under the toll and no-toll,it is found that under no-toll,expressway network part time operates in the right section of the MFD and even large deviation from the critical density is happened,which can easily cause traffic congestion,while the arterial network sometimes operates in a state of low density,that is,the utilization rate of arterial network is extremely low.After adopting the charging strategy,both the expressway network and the arterial network operate in the left part of the MFD.The traffic status of the road network is more balanced and the phenomenon of low utilization rate or excessive utilization of the road network is avoided,which indicates the effectiveness of the dynamic traffic charge of the road network combined with the MFD.This study can provide a theoretical reference for the further implementation of multi-modal and multi-region dynamic traffic management.