Model Construction And Vulnerability Analysis Of Tram-Bus Compound Transportation Network

With the continuous enrichment and improvement of urban public transportation,the intersection of tram lines and existing conventional bus lines makes the road network structure increasingly complex,and the emergency will cause immeasurable loss to the entire transportation system.Vulnerability is an indicator to measure the impact degree of network caused by emergencies.However,existing researches on vulnerability ignore the interlayer connections of different traffic networks in most cases.In addition,the research is relatively simple from both structural failure mode and evaluation index.Firstly,based on the complex network theory,the model of tram-bus compound network is established,and the centrality of the network is studied.Then a vulnerability evaluation model is proposed,which can be used to analyze the vulnerability of compound network and its subnetwork vulnerability.Finally,the importance of network nodes and edges can be evaluated based on the vulnerability.The main research contents include:(1)Taking the public transportation network in Yizhuang area of Beijing as an example,the tram and the conventional bus line network is abstracted into a topology structure.Based on the Space L model,the tram-bus compound network model is constructed,and the topology structure statistical characteristics of the compound network and sub-network are comprehensively analyzed.The result shows that the compound network is a small-world network with scale-free properties.The bus subnetwork efficiency increases by 17.81%after compounded with tram subnetwork,which indicates that the tram lines have a certain integration and convergence effect on the bus routes along the line.(2)The paper studies the structural centrality characteristics of tram-bus compound network and sub-network,and the important nodes are compared and analyzed from the perspective of structural centrality.At the same time,the centralization degree of different networks is analyzed based on the centrality index,the result shows that the non-homogeneity of tram subnetwork is strongest and that of bus subnetwork is weakest.(3)After establishing a vulnerability evaluation model from the perspective of network centrality,the paper conducts continuous attack simulation experiments on tram-bus compound network,tram subnetwork and bus subnetwork respectively.Then the changes of vulnerability index under different attack strategies are calculated.It is found that the three networks have lower vulnerability under random attack strategy and higher vulnerability under betweenness centrality attack strategy.The vulnerability of tram-bus compound network is lowest,and the vulnerability of tram subnetwork is highest.In addition,the concept of interlayer tightness is proposed,and the calculation result shows that the interlayer tightness of compound network is 0.2704,indicating that the degree of interconnection between the tram subnetwork and the bus subnetwork is relatively low.The inter-layer compactness is used as the vulnerability index to find that the eigenvector central attack strategy has the greatest damage to the compound network layer.(4)Based on the vulnerability assessment of the importance of compound network nodes and edges connection,it is found that the tram site has a greater impact on the compound network.In addition,vulnerability of the edges about 6.59%will be more than 0.01,so the impact of edge connection vulnerability cannot be ignored.Moreover,combining with the centricity to improve the evaluation method,the centrality-vulnerability index evaluation method is put forward,and the importance order of tram-bus compound network nodes and connecting edges is obtained.Then the distribution of important nodes and connecting edges are researched.The focal areas of emergency protection are divided into four areas:Hexi area,Hexin area,Majuqiao area and Ludong area.Finally,based on the evaluation results of the vulnerability of the tram-bus compound network,the emergency planning suggestions of the traffic network in Yizhuang are gazetted.The conclusion of this paper provides a theoretical basis for the research of vulnerability in compound network to some extent.