<p>Urban transport networks are increasingly navigated through digital platforms, yet informational support is unevenly attached to the systems it is meant to clarify. This paper develops the concept of the digital motility gap to describe a mismatch between realized mobility complexity and digital information intensity. Drawing on a representative travel survey of 5,003 Hong Kong residents and 20 semi-structured interviews with public-transport users, the study examines how informational usability is distributed across modes and lived in everyday travel. The findings show that rail combined physical and digital legibility, while buses, trams, and minibuses often required more interpretation, their usability shaped by unstable predictions and hard-to-read platforms on one side and by the language competence and local knowledge demanded of travelers on the other. Larger gaps appeared mainly through non-evaluation, with respondents more often selecting “no comment” than rating transport information as inadequate. Interviews showed how routine journeys, familiar circuits, and compact urban form could make informational unevenness less visible, while less familiar journeys remained exposed to the weakest parts of the information system. The paper reframes digital transport information as a condition of urban motility and identifies the usable city as a practical boundary between formal network availability and everyday mobility.</p>