This article explores how urban space produced by the Japanese railway system is appropriated by people for common use in Tōkyō. Drawing from ethnographic research among musicians at a central train station, I explore how individuals enmeshed within the schedules of the commuter network negotiate mobilities that fall outside the purview of railway urbanism. Station tsūro are passageways monitored by rail staff and local authorities, protected by traffic and railway commerce laws, and influenced by competing pressures from the overburdened network and local neighborhoods. Musicians sensitive to these shifting relationships identify leeway within, performing in ways that open tsūro up, producing temporary, finely balanced spaces of encounter and connection. Through these processes, the commuter system creates rail-specific forms of human relationships.