Enhancing robustness of metro networks using strategic defense

The safety of metro networks has recently attracted great attention. In this study, we investigated how to allocate security resources in a metro network to enhance its robustness through a defense-attack approach. For each defense-attack model, the defense strategy was first applied to protect a certain proportion of influential nodes in the network and then an attack was executed on the protected network. The influential nodes were identified by eight strategies, one of which, the breadth-tree coefficient strategy, is proposed as a new approach. Simulations of five metro networks showed that attacks on nodes with the highest betweenness centrality value are the most effective for disrupting a metro network, while the robustness of the metro network can be enhanced more efficiently with the proposed breadth-tree coefficient strategy. We also found that the robustness of metro networks benefits less from scattered protected metro stations, since some neglected weakly connected nodes emerge among the optimal influencers. The study also provided insights into how topological features influence the robustness of metro networks. It demonstrated that loop lines and smaller transfer stations can provide more options for alternative routes and be less vulnerable to targeted attacks, which makes the metro network more robust in the face of accidents and terrorist attacks. Our study provides useful information for metro network managers to take decisive actions on how to allocate security resources to increase the robustness of their metro network and design a more robust metro system. (C) 2018 Elsevier B.V. All rights reserved.