Transport accessibility is one of the most significant locational factors for both households and firms, and thus a potentially self-reinforcing driver of urban development. The spatial structure and dynamics of accessibility hence have the potential to alter the locational choices of households and firms significantly, leading to concentration and de-concentration processes. In spite of recent innovations in automotive technologies, public transport systems remain crucial for the functioning of metropolises. In this paper, we use the case of public transport in the Munich Metropolitan Region (MMR) in Germany to (1) discuss whether public transport in the past has contributed to regional urbanisation, the blurring of urban and suburban spaces; (2) model future accessibility changes due to the ongoing mega-infrastructure project “second trunk line” (“Zweite Stammstrecke”) for suburban trains and their likely effects on processes of regional development; (3) compare the balance of accessibility and functional density at stations in the MMR and (4) recommend a planning strategy based on an integrated urban and transport planning philosophy. We argue that particularly the monocentric design of the project means that it will intensify and extend the scope of suburbanisation and metropolisation, while planning should aim for a greater regionalisation of economic activity.