A preliminary study on the vulnerability of the Metro Taipei

The vulnerability refers to weakness and risk of a system and its recovering ability after suffering a disaster. It has been widely used to evaluate an ecological or an environmental system. In this paper, we introduce the three index, (1) exposure, (2) sensibility, and (3) adaptability, proposed by the IPCC of the United Nations, to evaluate the vulnerability of a transportation network - the Metro Taipei. The exposure is defined as the risk of accidents and the pressure on the network, such as the inundation scenarios and the passenger flow of a station. Once an unexpected event affects the system will cause tremendous inconvenience to the passenger. The sensibility is defined as the centrality of the network. Three centrality index of each node(station) are calculated: (1) degree, (2) closeness, and (3) betweenness, to find the sensitive nodes of the network. The degree centrality is the in-connections and out-connections of a node. The closeness centrality means how close a node is to other nodes of the network. The betweenness centrality reveals how many times a node would be passed through between any two other nodes. The Girvan and Newman grouping method is applied to decompose the network into sub-networks. A sub-network can be taken as a local network. The adaptability is defined as the recovering ability or the alternatives while a node is suffering an accident. The nearby bus stops and public bike stations are considered as the alternatives while a metro station is becoming disabled. The more bus stops or public bike stations means higher adaptability of a metro station. We propose an integrated vulnerability index to considering the exposure, the sensibility, and the adaptability of each station. The integrated vulnerability index is then visualized on the map for better illustration of the negative impact and the positive recoverability of the Metro Taipei.