Rethinking Compact City Strategies in Car-Oriented Regional Cities: A Multi-Modal Accessibility Assessment of 15-Minute Urban Living under Limited Public Transport Networks in Japan

The compact city concept has traditionally been associated with transit-oriented urban structures; however, many regional cities continue to rely heavily on automobile-based mobility due to limited public transport networks. This study raises critical questions regarding how future urban development strategies should be designed in car-oriented contexts. Using the concept of the “15-minute city” as an analytical framework rather than a normative goal, this study examines multi-modal accessibility to urban functional facilities in several regional Japanese cities.

A GIS-based network analysis was conducted to compare 15-minute accessibility across four transport modes—walking, bicycle, public transport, and private automobiles. Accessibility was evaluated not only in terms of spatial coverage but also in terms of population coverage, using high-resolution census mesh data. The analysis covers five regional cities and six types of frequently used urban facilities, including healthcare, retail, and administrative services.

The results indicate that automobile-based accessibility remains dominant in dispersed urban structures. In most cases, over 80–90% of the urban population can reach major facilities within 15 minutes by car, whereas the corresponding walking coverage remains substantially lower. Bicycles substantially expand accessibility compared with walking and provide moderate coverage in compact urban areas. Public transport improves accessibility in certain corridors; for example, the population reachable within 15 minutes increases by over 13,000 people in some cities, while in others the increase remains limited to only a few hundred residents, indicating significant spatial disparities.

Rather than advocating a universal transition toward transit-oriented compact cities, the findings suggest that future urban strategies in car-dependent regional contexts should adopt hybrid approaches that enhance local accessibility through walking and bicycle networks while strategically integrating public transport where feasible.