Abstract:  In contrast to the notion of the “useless city,” Japan has long engaged in the practice of repurposing the spaces beneath railway and highway infrastructure for a variety of uses, including commerce, dining, nightlife, industrial storage, and, occasionally, residential functions. The concept of undertrack (re)fill, however, specifically refers to 21st‐century urban regeneration initiatives that aim to adapt these interstitial spaces for programmes centred on social interaction and cultural expression, closely embedded within local communities. This study aims to develop a synthesised framework for understanding community spaces situated beneath infrastructural viaducts, focusing on two key adaptive processes: juxtaposition and addition. Employing a morphological approach, the research explores the spatial relationships between these interstitial areas, the infrastructure above, and the broader urban context, through several case studies in Yokohama and Tokyo. Methodologically, the study characterises each case through a combination of architectural drawings and photographic documentation, drawing on existing design projects. Notable examples include the Koganecho Art Centre in Yokohama, as well as sites in Tokyo such as the Elevated Garden at Nerima and the Chuo Line House Koganei in Koganei. These spaces encompass community centres, local art exhibitions, open‐air markets, and cultural venues, each contributing to a stronger sense of belonging and collective identity. By integrating local traditions and cultural practices into contemporary urban regeneration, Japan demonstrates how development can be both environmentally sustainable and culturally enriching.

Keywords:  community space; morphogenesis; railway infrastructure; undertrack refill

Published:   Ahead of Print

Issue:   Vol 11 (2026): Sustainable Urban Regeneration in Japan (In Progress)