Transit oriented developments (TODs), be they greenfields developments, in-fill or redevelopments of existing sites, have been included as a key component within a number of recent metropolitan strategies within Australia, including the South East Queensland regional plan. Responding to increasingly extended journeys-to-work and other trip movements, TODs are one land use planning intervention that creates the potential for populations to make shorter journeys and to make mode shifts away from the private motor car and towards walking, cycling and public transport. Whether TODs are led by private developers, development corporations or other entities, the majority will involve the design of a comprehensive structure plan to coordinate development of the site. The skill of designers and planners will ultimately determine how conducive to sustainable travel behaviour the end result is likely to be. Unfortunately, not all TOD designs will generate the desired outcomes and not all opportunities for travel behaviour improvements may be captured - reducing the effectiveness of the overall planning strategy. For instance, while there may be increased opportunities to reach line-haul public transport for longer trip purposes, designs could actually create less sustainable behaviours for other trip purposes, such as journeys to and from school or to and from local shopping. Part of the problem is that no decision-support tools are readily available to establish whether a specific TOD proposal actually provides the capacity for an improved mode share for sustainable modes, or for decreased journey lengths across a range of trip purposes. The paper suggests a way forward for the development of a diagnostic tool that can assist TOD developers and decision-makers to quickly assess the potential of developments and the likely travel behaviour produced by their design.