Rail network robustness: The role of rapid development and a polycentric structure in withstanding random and targeted attacks

In large-scale urban agglomerations, heavy rail in the form of metro and commuter train serves as the backbone of the metropolitan public transport network. Transport systems are subject to recurrent disruptions that may result in severe consequences for network performance and society at large. The objective of this paper is to compare the robustness of selected public transport networks which exhibit different properties to both random and targeted attacks and gain insights on the role of network structure and development pattern. The authors adopt a complex network theory approach, investigating network performances under alternative sequential disruption scenarios corresponding to the successive closure of either stations or track segments. Targeted attacks are simulated by the removal of the most central network elements. Network performance is measured both in terms of the capacity of the network to function in terms of connectivity as well as the impedance induced that remain connected. Two exemplary networks are selected – the polycentric Randstad region and the largest and rapidly developing Shanghai metro network. The results indicate that both networks are highly vulnerable to targeted attacks with the Shanghai network exhibiting greater robustness in all scenarios. The connections between the urban cores are most critical in the multi-centric Randstad network while the Shanghai network is most susceptible to disruptions in the edge of its core, risking cutting off its long branches. Our findings provide more nuanced insights on the relations between network structure and robustness.