Topological evolution of public transportation network: A case study of Bangkok rail transit network

Bangkok Rail Transit Network (BRTN) is the first urban rail transit system in Thailand, initially operated in 1999. Once completed in 2029, the BRTN will be one of the world largest urban rail transit networks, with 285 stations accounting for 508 kilometers of travel distance. To investigate and explain the topological evolution of BRTN from 1999 to 2029, five network indicators were selected, including network diameter, gamma index, degree centrality, closeness centrality, and betweenness centrality. We found that, as the BRTN evolves, both diameter and gamma index seemingly rise indicating better spread and connectivity over time. Likewise, average degree centrality increases from 1.91 to 2.27, while both average closeness and betweenness centrality gradually decline; but with different intensity patterns. More specifically, stations with high closeness tend to be those in the central Bangkok area as they conveniently reach the rest of the network with fewer links; however, as betweenness gives more weights to stations that facilitate transportation, stations with high betweenness tend to be those joining central area to the suburbs.