Scenario-based mobility simulation for shrinking cities using ABATA: A case study of Iksan, South Korea

Shrinking cities face complex mobility issues driven by demographic shifts, spatial contraction, and declining activity levels. They also undermine the effectiveness of conventional transportation modeling approaches. This study investigates how urban shrinkage—characterized by population decline, aging, and spatial reorganization—affects activity patterns and travel demand in regional cities. We introduce the ABATA (Activity-BAsed Traveler Analyzer), a web-based modeling system, and apply it to the shrinking city of Iksan, South Korea. Using ABATA, we analyze four scenarios: a 2024 base case and three alternatives for 2035 incorporating demographic and land use changes. The model integrates mobile phone data, household travel surveys, and census-block land use information to produce high-resolution hourly estimates of activity profiles and origin-destination flows. Simulation results reveal scenario-dependent variations in activity intensity, travel distances, and the distribution of trip purposes. Particularly, scenarios involving a larger elderly population and central area contraction show sharp declines in long-distance commuting, while decentralized land use patterns lead to a redistribution of demand toward peripheral districts. These findings suggest that policy efforts in shrinking cities should prioritize local accessibility, right-sized infrastructure, and scenario-based planning approaches. The study underscores ABATA's value in high-resolution, activity-based mobility analysis and its potential to inform strategic and adaptive transportation planning under conditions of urban shrinkage.