Statistical Analysis of the Metropolitan Seoul Subway System: Network   Structure and Passenger Flows
  The Metropolitan Seoul Subway system, consisting of 380 stations, provides the major transportation mode in the metropolitan Seoul area. Focusing on the network structure, we analyze statistical properties and topological consequences of the subway system. We further study the passenger flows on the system, and find that the flow weight distribution exhibits a power-law behavior. In addition, the degree distribution of the spanning tree of the flows also follows a power law. 
Keumsook Lee, Woo-Sung Jung, Jong Soo Park, M. Y. Choi