Evolution assessment of urban rail transit networks: A case study of Xi’an, China

Urban rail transit is a critical transportation infrastructure in easing traffic congestion, shaping urban’s layout and promoting economic development, especially in large cities. This study explores the evolution process of Xi’an rail transit network (XRTN). The principal component analysis (PCA) and a Gaussian mixture model (GMM) are applied, which divide evolution process into stages based on temporal topological data. The results show that the development of XRTN from 2011 to 2025 has significant phased evolution characteristics. In the initial and development stages, network coverage is expended, which improved the accessibility. In the improvement stage, network density increases, while the network connectivity is continued to improve. However, the importance of individual stations is polarized, and a few stations with higher node centrality are identified. The construction of a ring line with new transfer stations can effectively improve connectivity, robustness and service capacity, to ease congestion. The findings of this study reveal the spatio-temporal complexity of XRTN’s evolution process, which would be useful to serve as guidance for expanding the exiting network.