Research On Optimization Method For Urban Road Network Based On Special Characteristics

With the rapid development of economics, the traffic problems become more and more serious. The basic reason that makes traffic jam is the unbalanced between traffic supply and demand. Recently, the construction of the road is becoming more complete, and the construction of main roads in the urban was almost finished. In recent years, the area of road development in a stable speed, but the number of vehicle increase year by year. During the morning and evening peak hours, roads always became huge parking lots. The study of the optimization of urban road network not only can find the shortage of the current roads, but also can solve the problem of the traffic jam and improve the highway capacity. This paper built on the researches from domestic and foreign, based on the theory of the complex network, considered two different situations: city expressway-main road networks and main road-minor road networks and realized that in the current networks exist the situation that parts of the micro network do not belong small world networks. According to the problems in current roads network, finding the special carateristics for urban road network, getting the definition of the special networks, quantification the standard of the special network judgments. At the same time, through the analyses of the highway capacity find factors that influence the intersections and links. And define the heavy degree node and high value link, from this, which can easily find the heavy node and link in the network, in case of the optimization of the networks. Then, use GA-PSO hybrid algorithm to solve the bi-level model. Later, through the analysis of the example and verify the model practicability.This paper main research includes below:(1) Define the concept of special networks: consideration the exit and entrance, the main road and auxiliary road. By the method of topology the exist road networks, we find it is not consistent with the definition of a small world network, find the special characteristics of the urban network, and then define the special networks. Based on the theory of complex networks, selected the degree distribution, shortage path length, and the clustering coefficient as judgment factors, and use two examples to ensure that networks exist;(2) Propose special network characteristic values: through the research of influences that road network traffic capacity in intersections and sections, combined statistical characteristic value and complex network with the status qualification of road network, get statistical characteristic value of the special-shaped web: heavy degree node and high value link. The characteristic value can find out the important intersection and links in the networks, and play an important role in the later researches of urban road network optimization;(3) The research of urban road network optimization model: make the shortest user travel time to be the upper objective function, and the user equilibrium assignment model to be the lower of the objective function to established a bi-level optimization model, and use GA-PSO hybrid algorithm to solve and optimize the design of current road network;(4) Case analysis: use old city road network in Xicheng district in Beijing as an actual case. At first, prove the model is practical, based on this network have special characteristic. Then, calculation of the optimization results and purpose of the optimization scheme. Last, compare the road network property between the optimization before and later, and get the conclusion that the special characteristics of urban network become weak. Keywords: special characteristic, special network, influencing factors, Bi-level model.