A two-stage resilience promotion approach for urban rail transit networks based on topology enhancement and recovery optimization

Uncertain disruptions in urban rail transit (URT) networks can inflict significant damage to their structure and functionality. Enhancing network resilience has emerged as a critical solution to mitigate these challenges. This paper introduces a two-stage approach to bolster the resilience of large and intricate URT networks by focusing on pre-failure network topology enhancement and post-failure recovery sequence optimization. The assessment of network resilience encompasses the entire resilience process from the onset of a failure to the end of the failure to the completion of the recovery, and the resilience loss triangle model was employed as a valuable tool for assessing network resilience. Meanwhile, an improved resilience evaluation metric was proposed, which uses the global efficiency ratio as the network performance indicator. Taking the Shanghai metro (SHM) system as a case study, a distance-weighted network model was constructed to validate the effectiveness of the proposed resilience enhancement method. Based on the network failure simulation, vulnerable stations in the SHM network were identified and the influence of different metro lines was evaluated. Moreover, considering the existing network topology and practical planning, the topology optimization scheme for adding an outer loop line in the SHM network was developed. The results demonstrate that the topology-optimized network can effectively enhance the network resilience and protect the vulnerable nodes. Additionally, corresponding optimal recovery sequences were proposed for the failure of a single node, multiple nodes, and multiple edges. An interesting finding is that the optimal recovery order is not dependent on the node degree but rather associated with the node vulnerability. Furthermore, it is demonstrated that optimizing the post-failure recovery sequence helps reduce network resilience loss, whereas improving the network topology prior to failure plays a more significant role in promoting resilience. Hence, the proposed methodology and research findings can serve as a valuable reference for the development planning and emergency management of public transportation systems.