Xi'an Bus Network Static Topology And Its Optimization Investigative Studies

In recent years, large cities at home and abroad are making great efforts to look for effective measures to improve the city traffic conditions. In the case that the traffic resources of our country are limited, making analysis and optimization of urban traffic networks is the only way of enhancing the efficiency of traffic resource and relieving the urgent situation of urban traffic to the largest extent. Urban traffic networks are typical, open, complex and huge systems. In order to optimize and improve the urban traffic network, the topological structure of the urban traffic network of Xi'an is studied and explored from different angles,which is based on the theory of complex network.This paper follows the general pattern of modeling to study Xi'an public transportation systems. Based on the real-life network, the paper started from network macrotopological features of Xi'an urban public transportation and divided the urban public transportation system into three different models: the traffic-station network, traffic-line network and public-transit network. The paper analyzed Xi'an urban public transportation system by introducing some basic and important topological parameters such as node degree, degree distribution, clustering coefficient, average shortest path length, node weight and edge weight and node betweeness and so on. These topological parameters, of which the concrete meanings were studied from the perspective of transportation engineering, were calculated and analyzed to investigate Xi'an urban traffic networks.In this paper, Xi'an City traffic-station network, traffic-line network and public-transit network are all modeled into undirected weight networks. Urban traffic-station network is used to study connectivity between bus stops, in which vertexes stand for bus stations; and there is only one edge between two stations if the two stations belong to the same bus line when they are neighbors. The number of lines between the two neighbors is defined as edge weight; the number of lines of a bus station is defined as vertex weight. Urban traffic-line network is used to study connectivity between bus lines, in which vertexes stand for bus lines; and there is only one. edge between two bus lines if they have the same stations. The number of same bus stops of the two lines is defined as the edge's weight; the sum of all edges' weights of a vertex is defined as vertex weight. Urban public-transit network is used to study line change at bus stops. Bus stations are represented by vertexes,and there is only one edge between two stations if the two stations belong to a bus line; the number of bus lines linking between the two stations is defined as edge weight.Deep investigation of the paper proves that the traffic-station network, traffic-line network and public-transit network of Xi'an all have the small-world and scale-free properties since their average shortest path lengths are all relatively short and their clustering coefficients relatively big. It is still found that the degree distributions of the three networks are not followed power-law distribution but get near to poisson distribution in which it does not bring fatal impact even if vertexs with big degree or big node's weight are deleted. Through holistic investigation of the topological structure of Xi'an urban traffic network, it is revealed that Xi'an Public transportation system is under development as a whole; topological structure is unreasonable, and efficiency of bus transportation is relatively low. Therefore, Xi'an urban traffic networks need to be improved and optimized further.Finally, the paper, based on the real-life network study, from the angles of transportation engineering and city planning, brings forward the network optimization proposals of building such traffic system with different functions and gradations in Xi'an. Through such optimization, Xi'an urban traffic network will take on a complex network structure with communities, and its whole efficiency of bus transportation will be improved greatly.