Study On Time Dependent Characteristics Of Traffic Stream At Urban Expressways

Traffic congestion affects greatly the further development of urban and people's travel. Building expressways to alleviate city traffic pressure is an important channel to solve traffic congestion. But now, the result is not ideal. There often occur traffic congestions at expressways; therefore, it becomes urgent to prevent or alleviate traffic congestions at present.The dissertation is based on the doctorate subject fund of MOE "Study on Theories of Bottleneck Forming, Diffusing and Controlling in Urban Expressway System", the Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOE "Study on Theory of Controlling Urban Expressway System" and the Key Project of National Natural Science Foundation "Research on the principal theoretical model and simulation technique of dynamic traffic management and control in urban network". The paper mainly studies time dependent characteristics of urban traffic flow at expressways. It is aiming at finding the transformation rule of expressway's traffic flow and providing theoretic foundation for the management and control at expressways.To achieve a non-congestion state as possible, it is necessary to analyze the characteristics of urban traffic flow in course of traffic state change at expressways. There is analysis over time characteristics (i.e. time dependent characteristics of flow parameter) of traffic flow transformation in Chapter 2. First in accordance with the requirement of the project, a method of data gathering and processing was confirmed. Then through field observation, samples of congestion occurrences were collected at the expressways. By analyzing the data of congestion, it is found that speeds change quickly. Occupancies change quickly at the exits and entrances free from impact or little affected, while change gradually when the exits and entrances are heavily affected. All the parameters of traffic flow fluctuate within a certain range.To ease the traffic congestion at urban expressways, two traffic states should be definitely separated at urban expressways: the congestion state and the non-congestion state. As a result, it is important to define traffic state change time. In Chapter 3, after a review over the application of accumulative curve, the conclusion comes out that flows descend and occupancies ascend when a certain spot in traffic state converses from non-congestion state to congestion state, and...