Characterizing a Long-Time Evolution of Metro Network Topology: Evidence from Metro Networks in 34 Chinese Cities

The development of urban metro networks is crucial for planners and policymakers in addressing sustainable urban development. This study collected metro network data from 34 cities in China and utilized a three-dimensional model to perform a topological analysis of these networks, aiming to identify successful practices. The service degree of population demonstrated a strong correlation with the topology of urban metro networks. The topological analysis revealed three phases in the evolution of metro networks: (1) central densification; (2) outward expansion; and (3) preferential development. Throughout this process, the complexity of metro networks tends to reach saturation, and transfer convenience is enhanced, resulting in a reduction in the number of transfers required during travel. Furthermore, the implementation of ring lines was effective in improving the state features of metro networks during the early stages. Increasing the ratio of radial lines can maintain network simplicity and enhance transfer convenience. The findings of this study provide insights for policymaking in the development of urban metro systems.