Public transport is a challenging environment for both passenger and operator. The operation of large networks carries expectation of timely delivery of passenger-oriented services. With numerous stakeholders such as government, private industry, and the general public the expectation around the primary concept of mobility within transport networks often differs. This chapter examines how data visualisation has been engaged to better understand an enduring mobility challenge of Australian metropolitan rail networks, the universally accepted accessibility issue widely known as ‘the gap’. With increasing global requirements for disability compliance and anti-discrimination within public transport, data visualisation is applied within a broader design project. Engaged at the problem-definition stage this data-driven approach provides investigators greater insight and visual transparency towards understanding the impact this issue has on mobility for all users of public transport.