The Study Of Vulnerability Of Urban Rail Transit System

With the rapid development of urban rail transit, more and more subway system go into service with the large scale network and extending passenger flow. As the aorta of the urban public transport, a large population swarm into in a relatively closed underground space in a short period of time; once the accident occurring, it is likely to cause traffic block and mass casualties because of the inconvenience of ventilation, escape and rescue. Therefore, it is urgent to analyze and evaluate the vulnerability of urban rail transit system by using experience, model, data and decision support tools.Based on safety science, system theory, complex network theory, and computer simulation technologies, the urban rail transit system vulnerability was made a thorough study. This research analyzed the main factors which influence the urban rail traffic vulnerability, and established the assessment model of if from the aspects of component vulnerability, network structure vulnerability and social function vulnerability, then the paper take Beijing Metro as the empirical analysis to provide a new perspective and theoretical basis for urban rail transit system of design and management. The main research work of this paper is as follows:(1) Analyzed the connotation and framework of vulnerability of the urban rail transit system.According to the current domestic and foreign vulnerability theoretical research, we summarized the concept and connotation of vulnerability and discussed the difference of reliability fragility and other related concepts. On this basis, we defined the concept of vulnerability of urban rail transit system, and analyzed the internal dimension and external performance of it, which is divided into component vulnerability, network structure vulnerability and social function vulnerability.(2) Analyzed the main influence factors of vulnerability of the urban rail transit system and established identification model of it.In the view of the system, the vulnerability factors of urban rail transit system were extracted according to the analysis of typical accident. With the purpose of developing an identification model of vulnerability factors for urban rail transit system, the combined method was proposed which integrated three kinds of method including the DEMATEL, the ISM and the ANP. The hierarchical network structure model of vulnerability was developed using the integrated DEMATEL-ISM-ANP method which took into account of the interactive influence direction and intensity of the factors, structure of the factors, and the relative importance degree of the factors. According to the analysis results of hierarchical network structure model, the vulnerability factors of urban rail transit system were divided into four types:driver, linkage, dependent, autonomous. It is shown that the model of integrating the DEMATEL, the ISM and the ANP is appropriate for quantitatively analyzing the vulnerability factors of urban rail transit system.(3) Built evaluation model of the component vulnerability of urban rail transit system.According to the influence factors of vulnerability of urban rail transit system and the cause analysis of accidents, the factors of componenting vulnerability of urban rail transit system have been divided into three groups including personnel, equipment and environment. In the view of a system, the combined assessment method has been proposed which integrated three kinds of method including the DEMATEL, the ANP and the Fuzzy Matter Element. Used the DEMATEL-ANP-Fuzzy Matter Element model, six typical Beijing Metro’s stations have been assessed to verify the validity of the model. It is shown that the model of integrating model is appropriate for quantitatively analyzing the components vulnerability factors of urban rail transit system.(4) Built evaluation model of network structure vulnerability of urban rail transit system.Based on the construction of urban rail transit system physical network model, we selected the structure entropy, network efficiency and maximal connected subgraphs as index to analyze the network structure vulnerability of the urban rail transit system. Through the simulation example of Beijing subway network, we studied the basic characteristics of it, and the changing condition of the selected index at the random attack and intentional attack. Studies show:the network of Beijing rail transit system has poor robustness and high vulnerability in condition of calculated attack; while in the case of random attacks, the network has strong robustness and low vulnerability. This shows that the subway station has different importance in the whole network.(5) Built evaluation model of social functions vulnerability of urban rail transit system.According to the urban traffic system time network model and transportation network model, we established the subway station’s social function vulnerability assessment index and evaluation model which used VIKOR method. On the basis of this, the network efficiency vulnerability, time efficiency vulnerability and transport efficiency vulnerability were selected to measure the social function vulnerability of the urban rail transit system. Through the simulation example of Beijing urban rail transit system, it is shown that the model is appropriate for quantitatively analyzing social functions vulnerability of urban rail transit system. From the overall perspective, the social function vulnerability of Beijing rail transit system presents an irregular "saddle", which the vulnerability of early peak is higher than the late peak.