How urban metro networks grow: From a complex network perspective

Abstract

Metro lines emerged and developed in cities driven by various factors, and resulted in different structures as we see today. How do metro lines grow as a system? The spatiotemporal growing patterns of metro networks and their complex-network statistics may shed light on this question. Within the framework of the complex network analysis, this paper establishes a nine-metric scheme to quantify the service performance of an urban metro network from three dimensionalities i.e., accessibility, resilience, and serviceability. Accordingly, a shamrock plot is proposed as a tool to visualize the multi-dimensional maturity of a metro network as well as its growing pattern. The metrics and the visualization tool are used to reveal metro development in 42 cities of Chinese mainland. The results show that metro networks can evolve from nascent, to skeleton, and to mature forms, with their scores increasing in all dimensionalities. The choice of urban transportation between metro-dominant and automobile-dominant results from the race between metro development and car popularity. Cities may be more likely to become metro-dominant if metro develops early at a low level of car ownership. Urban metro network may develop as a response to the city’s needs hierarchically from the most basic (e.g., accessibility) to more advanced (e.g., resilience and serviceability), similar to Maslow’s hierarchy of individual needs.