Study On Formation Mechanism And Evacuation Optimization Method Of Oversaturated Phenomenon At Intersection Groups

With the rapid development of social economy, the living standard of residents is steadily improved, more and more families choose to purchase cars, and vehicle retention has been increased promptly, which causes enormous pressure to urban road network. Especially at the intersections where vehicles from different directions convergence interlace and interfere with each other, the capacity is lower than that of the midblock segment capacity, thus becoming the bottlenecks of roadway network, and easily triggering traffic congestion. Therefore, study on oversaturated phenomenon at intersection groups is helpful to understand urban congestion and to make corresponding urban traffic congestion solution scientifically.This thesis focuses on the formation mechanism and evacuation optimization method of oversaturated intersection group, which is helpful to identify, control, evacuate and evaluate oversaturated phenomenon.This paper firstly analyzes the traffic characteristics of oversaturated intersection group, and predisposing factors of oversaturation are described for the signalized intersections. Then by employing the concept of System Dynamics(SD), the SD model of average saturation for intersection group is established, and the order degree and road adhesion coefficient are exemplified for analysis by making use of VENSIM software. The simulation results demonstrate that degree of order has obvious effects on the average saturation, and a high degree of order is beneficial to reduce the average saturation, so as to reduce the possibility of oversaturation.After that, the evacuation optimization theory for oversaturated intersection group is investigated. By referring to Particle Swarm Optimization method, first, the Analytic hierarchy Process(AHP) is adopted to determine the optimal control goals: the continuity of vehicle travelling during the process of evacuation and the shortest evacuation time. By making advantage of VISSIM simulation software evaluation index is obtained and the fitness degree is calculated, therefore evacuation schemes are comparable.Finally, based on the assumption of well-shaped road network, the evolutionary process of applying PSO to optimize the evacuation control schemes of oversaturated intersection group is demonstrated, and the results show that the optimization algorithm is feasible.