A cost-and-effect simulation model for compact city approaches: A case study in Japan.

Japan's compact-city policy addresses rapid population decline and aging to ensure sustainable development. However, its implementation requires significant time, financial resources, and complex stakeholder collaborations. Faced with these challenges, we asked: How can the cost-and-effect of planning be simply and automatically recognized by stakeholders? To address this, a simulation model was developed for evaluating urban planning strategies within the compact-city framework. Our model integrates pseudo-people-flow data and includes three fundamental modules and five sub-models to simulate and predict urban metrics, including population, administrative costs, visitors, and traffic volume from 2015 to 2040. Four scenarios-baseline, location optimization, new road and new station installation-were analyzed. Findings suggest that 1) new station project could mitigate population decline, 2) both location optimization and new station projects improve public services efficiency and sustainability, 3) urban vitality could be enhanced by new station construction, generating a new urban core, and 4) compact city policy may also reduce and concentrate traffic volume, shortening car trips. The model's efficiency and uncertainty were examined, and user experiments highlighted the potential of digital tools to democratize urban planning, making it accessible for non-expert stakeholders and fostering informed participation. This research advances the use of technology in participatory urban planning. • A cost-and-effect simulation model is developed for compact city approaches, integrating multiple modules and sub-models. • The model predicts future administrative cost, population, number of visitors, and traffic volume from 2015 to 2040. • Conducted a comparative analysis of four development scenarios under compact city policy framework in Japan. • Demonstrated the model's computational efficiency, integrating into a web application for participatory urban planning. • Highlighted digital tools' role in urban planning, advocating accessible technology for informed decisions for non-experts. [ABSTRACT FROM AUTHOR]