A Study On The Dynamic Characteristics Of Urban Traffic Flow

As an important subsystem of Intelligent Transport Systems, the urban traffic control system has a significant effect on reforming traffic order, improving traffic safety, decreasing environment pollution and so on. From the point of view of control theory, the control system design methods are mainly based on the dynamic characteristics of the controlled object. Therefore, in order to control urban traffic flow more effectively,its dynamic characteristics must be studied. However, due to the intrinsically uncertainty and complication of urban traffic flow, the study of its dynamic characteristics based on control theory is a difficult job all along.Some main aspects, which were studied in this dissertation, are presented as follows:The importance of studying the dynamic characteristics of urban traffic flow was pointed out based on the limitations of the existing urban traffic control methods. The transfer function of a controlled object is a mathematical expression of its dynamic characteristics. However, it cannot establish a uniform transfer function for urban traffic flow directly due to its nonlinear and time-varying characters. A method was presented to study the dynamic characteristics of urban traffic flow, which was based on decomposing it into many discrete linear constant subsystems under certain conditions. The transfer functions of these subsystems were established based on system identification methods. Their dynamic characteristics were analyzed quantificational by the system and structure parameters of the transfer functions. At last, using the dynamic characteristics of these subsystems, the urban traffic flow was looked upon as one system based on the Systems Science.A general model structure was presented to describe urban traffic flow. Some typical dynamic units were presented to describe the traffic flow of an intersection and main roads, which are the representation of the road network traffic flow. The study was carried out by means of simulation experiments. In order to get the input/output data of the simulated traffic flow under different conditions, many different simulation experiments were designed. Using the input/output data, the transfer functions of the traffic flow of an intersection and main roads were established based on the methods of system identification. Therefore, the dynamic characteristics of the traffic flow of an intersection and main roads were analyzed. Some general conclusions were got: the transfer functions of the Cycle control channels are three-order systems; the transfer functions of the Split control channels are two-order systems; the transfer functions of the Offset control channels between adjacent intersections are three-order systems; all the dynamic units of urban traffic flow are stable, and their output pulse response sequences are oscillated and convergent.In order to develop the research results of the dynamic characteristics of urban traffic flow into urban traffic control practice, a method to classify urban traffic flow states at intersections based on its dynamic characteristics was presented. Based on its dynamic characteristics parameters, the traffic flow of an intersection can be classified into three different states: free flow, synchronized flow and wide moving jam. Moreover, the basic architecture of urban traffic variable structure and optimal control system was designed based on variable structure control and optimal control theory. The design method of the optimal controller of the new control system was presented. The proposal of the new control system is a new vision of the application of modern control theory in the urban traffic control field.