臺北捷運路網結構之脆弱度分析

Vulnerability Analysison the Taipei Metro Network

自1995年3月28日通車營運以來，台北捷運系統已成為大台北地區最主要的公眾的運輸系統。惟近年來陸續發生納莉風災淹水、電路系統故障、隨機砍人等事件導致捷運站點甚至全線系統中斷營運，使社會付出重大成本。為找出臺北捷運路網中最脆弱的站點，本研究引用聯合國跨政府氣候變遷小組（Intergovernment Panel on Climate Change, IPCC）所定義的脆弱度（vulnerability）影響指標：暴露度（exposure）、敏感度（sensitivity）與調適力（adaptability），以分析臺北捷運路網結構之脆弱度。首先將台北捷運路網已捷運車站為節點（node），前後站之間視為具有方向性的連結（arc），組成抽象性的位相關係（topology）路網。利用捷運旅運人次數據作為暴露度因子，在使用路網分析的中心性指標（centrality)找出路網結構中易受影響的敏感站點，最後將周邊其他互補運具視為調適能力，計算整體路網結構之脆弱度，嘗試找出路網中最脆弱的站點。本研究結果發現路網中脆弱站點多為轉運站之外，另有善導寺與雙連站因高敏感度被挑選出，調適能力以市政府與劍潭站為佳，但仍有多處高脆度站點需要提升調適能力，以因應意外事件萬一發生，能即時透過其他系統輸運旅客。

Vulnerability refers to weakness or risk for a system and its ability to recover after a disaster. It is used to evaluate an ecological or an environmental system. This paper uses the three indices to evaluate the vulnerability of a transportation network–the Taipei Metro system : (1)exposure, (2)sensibility and (3)adaptability. These are proposed by the IPCC for the United Nations. Exposure is defined as the risk of accidents and the pressure on the network, such as the potential for flooding or the passenger flow for a station. When an unexpected event affects the system significant inconvenience is experienced by passengers. The sensibility is defined as the centrality of the network. Three centrality indices for each node (station) are calculated: (1)degree, (2)closeness and (3)between-ness. These determine the sensitive nodes for the network. The degree-centrality is defined by the in-connections and out-connections for a node. The closeness-centrality is defined by the proximity of a node to other nodes in the network. The between-ness-centrality us defined by the number of times that a node is passed between any two other nodes. The adaptability is defined as the ability to recover or the alternatives when a node suffers an accident. The nearby bus stops and public bike stations are considered as alternatives while a metro station is disabled. The greater the number of bus stops or public bike stations, the greater is the adaptability of a metro station. This study proposes an integrated vulnerability index to determine the exposure, the sensibility and the adaptability of each station. The integrated vulnerability index is then visualized on the map to better illustrate the negative impact and the positive degree to which the Taipei Metro system can recover.