Modeling And Simulation Of Urban Road Traffic Network Based On Hybrid Petri Nets

With the development of economy, the traffic problems are more and more serious, which urgently calls the related ministry to strengthen the traffic management and control. Traffic lights method is one of the major methods for traffic control. As a result, it is necessary to model, analyze and simulate the urban traffic network in order to obtain an optimal or better traffic light timing plan.In the thesis, a modular frame based on hybrid Petri nets is proposed to model the signalized urban traffic network for control purpose. A kind of level of detail modeling methodology is used in this paper. After an aggregate model of the urban traffic network system is defined, the key elements such as traffic lights and intersections, which describe the typical feature of the traffic network in the aggregate model, are refined to introduce detail models. The proposed model of the intersection describes the turning direction of each traffic flow explicitly and takes into account the conflicts among the traffic flows. Furthermore, the time factor is considered in the system model. As a result, the total model obtained can not only reflect the logical relationship among the traffic flows, but also describe and calculate the physical characteristics of the vehicles such as the location, velocity, and passing time interval.The model simulation is another important item of the thesis. We design proper data structure for the model, which consists of discrete part and continuous part. After the simulation procedure gets the data needed, parameters of all kinds of data typed are created and initialized. Then, the simulation begins. The simulation process has two steps, one is the simulation of traffic lights, the other is the simulating of the whole traffic network under the control of the traffic lights. As the simulation cycle is divided into a certain number of simulation intervals or steps, the simulation procedure deals with every transition of the system model in a certain proper order. If the considered transition is enabled, fire it and modify the continuous token numbers in the preset and post set of the transition.During the simulation process, the performance index of the traffic light timing plan can be calculated simultaneously. As concerned in the thesis, the performance index are average queue length (AQL) and average time delay (ATD). Consequently, the performance index can be calculated with less effort for a given traffic timing plan and different timing plans can be compared in order that an optimal or suboptimal traffic control plan may be chosen. Finally, the system model evolution of a simulation example has been implemented and validated.The methodology of modeling, model analysis and simulation given by us concerns the urban traffic network in the real world. The methodology has the character of hierarchy and modular, since the skeleton model and the detailed model are obtained respectively during the modeling process. At the same time, the key element parts have their own sub models. As soon as the related data are input, the model simulation and the calculation of performance index can be acted automatically, since the level of detail operation during the modeling process is coherent and seamless.