Studies On Congestion Propagation Properties And Dissipation Control Strategies Of Urban Road Traffic

Road congestion is one of the most representative aspects of urban traffic problems, which has become one of the most important factors that influence people's travel quality and travel cost in daily life. Meanwhile, it also brings out some intractable problems with wide attention from the whole society, such as traffic safety, environmental pollution, and traffic energy consuming problems. Currently, congestion alleviation and prevention have become urgent tasks for urban development in our country, which can directly influence city sustainable development. However, human beings have not comprehensively understood the principle of road congestion propagation and the mechanism of congestion dissipation, which brings about blindness when people resolve urban traffic congestion in practice, and prevents traffic engineers developing effective measures to alleviate and control congestion. Therefore, detailed study of the sources of traffic congestion, congestion propagation characteristics and dispersal principles is a basic work to resolve congestion problems.The aim of this dissertation is to investigate the propagation mechanism of urban road congestion and develop some typical effective methods and strategies to control traffic congestion with the aid of dynamic network traffic flow theory. The main contents of the dissertation are summarized as follows:(1) The cell transmission model (CTM) is improved to formulate a dynamic network traffic flow model. Compared with the original model, the improvements are:the hysteresis effect of road traffic can be represented in CTM link model, and both signal control and road channelization at intersections are considered in CTM node model. In addition, a novel approach to calculate link travel time and route travel time is presented, and a group of indices are proposed to evaluate traffic congestion both on link-based level and on network-wide level.(2) CTM is extended to simulate the propagation principle of incident-based traffic jams. Traffic jam size and congestion delay are applied to measure jam growth and dispersal. The effect of stopline width assignment, length of the channelized area, incident position and link length on jam formation and dissipation has been studied. According to the spacial structure of traffic jam propagation, vehicle movement bans are taken as temporary traffic management measures to develop jam control strategies which are combined with linear control and area control. Simulation results show that the proposed strategies with appropriate application can effectively control jam dissipation.(3) A dynamic stochastic route choice model based on cross nested logit model is proposed. The dynamic network traffic flow model based on CTM is used to investigate the problem of congestion bottleneck identification under dynamic stochastic user equilibrium (DSUE) condition. Average journey velocity is employed to establish critical standard for defining congestion bottleneck. The relationship between traffic demand and bottleneck formation is highlighted. Furthermore, the process of bottleneck growth and distribution in the network are illustrated.(4) Signal control optimization and reasonable road channelization at intersections are important components of urban traffic organization, and one of the most effective solutions to depress traffic jams. Taking the equilibrium of the capacity of each flow direction as the objective, a max-min optimization model is proposed to investigate fixed timing plan methods and dynamic timing plan methods. Furthermore, the model is extended to formulate a combined problem of signal control and channelization at road exits. A solution algorithm is also proposed to solve the combined model. Under dynamic stochastic user equilibrium traffic condition, the validity of the proposed signal control method and channelization approach is demonstrated. In addition, congestion analysis and congestion bottleneck identification are carried out for the traffic network with optimal control.(5) Turning restriction is one of the commonest traffic organization measures and an effective lower cost traffic improvement method in urban traffic network. Reasonable turning restrictions can be applied to alleviate network wide traffic congestion. In this paper, a bi-level programming model is proposed to formulate the turning restriction design problem which considers network traffic dynamics. The upper level problem is to minimize the total travel cost and take signal control and road channelization into account from the points of traffic managers, and the lower level problem is to present travelers'route choice behavior based on DSUE theory. A genetic algorithm is designed to solve the proposed bi-level optimization model. Computational results show that the optimized turning restriction methods in congested network not only can improve network collective performance effectively, but also can reduce the scale of network congestion bottlenecks remarkably.