Topologic characteristics and sustainable growth of worldwide urban rail networks

The urban rail network system plays a significant role in the urban transportation system and urban economic development. Further study of the urban rail network properties can provide additional guidance to related scholars and designers. This study explored urban rail network properties worldwide, including assessments of their static and dynamic network topologic characteristics. Statically, this study analyzed various related network topological indicators for all of these urban rail networks. We found that, with increasing network size, the average degree slightly increases while the complexity and connectivity decrease. Using the Kolmogorov–Smirnov goodness-of-fit, the scale of the degree interval of these cities is [3.5 12.2]. Approximately 90% of these cities have network efficiency values less than 0.12, and 78% of these cities have lower assortativity coefficients. Focusing on the sustainable growth of rail networks, this study tested some specific networks to further deliberate their network expansion ability, network growth, and network robustness properties. The network expansion capability of small networks is relatively poor, while that of large networks is relatively strong. A simulation of network growth suggests that the connection of nodes with the maximum path length will seriously affect the efficiency and characteristics of the network. The robustness of the network indicates that adopting the maximum nodal degree elimination strategy will affect the function of the network. The results provide essential reference information for the rational planning, structural optimization, safe operation and sustainable growth of rail transit networks.