Research And Application Of Macroscopic Fundamental Diagram About Urban Road Network

Large and medium-sized cities more or less face the traffic congestion problems during the peak period wherever in developed countries or developing countries. Simultaneously, other serious traffic problems, such as gradually increased accidents, frequent conflicts, aggravation of pollution and so on, will arise due to the low efficiency of vehicle flow. In order to improve the operation efficiency of vehicles, traffic managers has carried on a series of practice from node, roads and road network respectively. Practical results have shown that the improvement strategies based on both single-point signal control and trunk signal control have little effect on alleviating road network congestion when the degree of correlation between intersections is high. Therefore, the macroscopic traffic control strategy based on research about traffic zone has become a hot issue gradually.Macroscopic Fundamental Diagram model(MFD) is based on the basic attributes of network, which could describe the basic relationship between the road network traffic flow parameters(flow rate, density and speed). Due to the actual characteristics of road network MFD reflects, it can provide more scientific and rational guidance for the monitoring and management of the urban road network. This paper will do some research on Macroscopic Fundamental Diagram model about the urban signal control network from the following three aspects, which are network characteristics, influence factors and theory application. The main research content is as follows:(1) A newly defined MFD is proposed based on the relationship between the number of moving vehicles(N) in the network during a certain time interval(?t) and the regional output flow rate(G) during the same time interval(?t). Then, the rationality of the model is analyzed and a practical method of mapping the MFD curve based on the new definition is developed. This method provides the technical support for the follow-up studies.(2) The existence and inherent laws of the newly defined MFD of the network is verified in two case studies both in a simulation environment and in an actual road network. According to the analysis of basic evolutionary trend and the characteristic about the macroscopic fundamental diagram, the researcher verifies the feasibility of using MFD to determine the network carrying capacity and an experimental test has been designed to validate the conclusion.(3) Considering the impacts the proportion of large car has on the shape and evolutionary trend of MFD, a sensitivity analysis has been carried on. And the change and law about MFD under different proportion of large cars is summarized. Then, a mathematical model of vehicle conversion coefficient based on the MFD is built and solved according to the result about the analysis of the sensitivity. The results of case shows that vehicle conversion factor only associated with vehicle composition when the road network traffic travelling in a free state; the vehicle composition and the number of moving vehicles will influence the value of vehicle conversion coefficient when the road network traffic is in a state of saturation or supersaturated flow.