Exploring Cascading Failure Process of Metro–Bus Composite Networks: A Two-Layer Network Perspective

The reliable operation of metro–bus composite networks (MBCNs) is critical to urban sustainable development. In this paper, we propose a two-layer metro-bus composite network (TL-MBCN) model that captures interactions between the topological structure and the spatiotemporal heterogeneity of passenger flow. An extended couple map lattice (CML) model is proposed to simulate the cascading failure process in MBCNs, incorporating passenger flow redistribution and station capacity. Four indicators are proposed to capture structural degradation, passenger flow loss, and service efficiency decline under disruptive events. Using real-world traffic data from Nanjing, we analyze the cascading failures in the MBCN based on the proposed framework. The findings reveal that (1) the MBCN exhibits greater robustness during off-peak hours compared to peak hours; (2) cascading failures are more easily triggered under strength-based attacks than under other attack strategies; and (3) metro stations with high degree and strength, as well as the bus stations that function as the hubs for local regions, are critical stations in the MBCN.