Study On The Macroscopic Fundamental Diagram Based On Simulation

Traffic flow characeristics, especially the relationship among flow, density and speed, is the foundation for road service level determination and traffic management stratergy establishement. Models of section or single link traffic flow characteristics are not meet the needs for nowadays, since traffic conjestion has spread to network wide. For this reason, many researchers have set their attention to macroscopic fundamental diagram (MFD), and few accomplishments have been made until now. Most studies argued the macroscopic flow can be influenced by macroscopic density and its heterogeneity, but few efforts have been made to confirm an model to explain the exact relationship among the three parameters. As a result, studies on influencing factors of MFD are qualitative analysis which failed to expain why these factors can change the shape of MFD. This paper studied on the exact model for MFD based on the flow-density model for basic road section using simulation software, and explored the influence on parameters in the model. This paper mainly studied the following components:(1) Use the simulation model of basic road section to obtain traffic flow parameters, and select a suitable model to make linear regression for flow and density relationship. A two-regime model had been proposed to describe the relationship between flow and density for a basic road section. Later prove lane number and green split have significant influence on model parameters: modle cuve of more lane number (larger green split) road lays above the one of less lane number (smaller green split).(2) To obtain relationship between macroscopic flow and density, take road network as the study object. Then analyse the flow and density relationship of each road section in the network, and the relationship between network MFD and each road section’s FD. An exact modle form among macroscopic flow, macroscopic density, density heterogeneity and the ratio of road section at different density range had been deduced, based on the flow-density relationship model for basic road section. The upper and lower bound of the relationship between macroscopic flow and density had been confirmed by analyzing the varied value range of the parameters.(3) Taking the former two parts as the basis, explore how route choice behavior and imhomogeneity of network can influence the shape of MFD and the parameters of the model based on the proposed macroscopic fundamental diagram model. Results showed that a resonalble route choice can balance the spatial distribution of density at each time slice, which can significantly increase the maximum macroscopic flow and desity with the same traffic demand; imhomogeneity of network can decrease the maximum flow of some road section, and increase the spatial distribution of density in the network, which will significantly decrease the maximum macroscopic flow and density of the whole network.