Deciphering long-term evolutionary patterns in inter-city travel networks in South Korea: Growth and decline of cities in association with inter-city connections

This study delves into the long-term dynamics of inter-city travel networks in South Korea by scrutinizing forty years of origin-destination data from both railway and highway systems. We uncover a pattern of increasing disparity in travel demand, concentrating more within certain hub cities over time. This trend points to an escalation in the prominence of these hubs, which have strengthened their connections with each other, emerging as critical nodes in the travel network. Meanwhile, non-hub cities have witnessed a decline in both population size and travel demand. Interestingly, while both railways and highways share a common trajectory toward centralization around hubs, they serve distinct roles. Highways have primarily expanded to connect neighboring cities, enhancing regional accessibility. Conversely, railways have evolved to cater to the long-distance connectivity of widely dispersed hub cities, reinforcing the role of these cities as key inter-regional links. These findings carry important implications for urban development and spatial planning. The evidence suggests a shift toward the formation of mega-regions, defined by a network of interconnected hub cities. Understanding the growth patterns and evolving connections of these expansive urban areas provides critical insights for informed urban planning and policy-making, ensuring that future developments align with the shifting landscape of urban connectivity and growth.