TOD should mean land use forms that reflect the nature of the transport system around which it concentrates. There are three basic forms of TOD:
- concentrated (walking distance) catchments, often with mixed land uses, around well-spaced high-capacity transport nodes
- linear concentrations along road-based public transport routes (corridors and “Main Streets”)
- development over a larger district with feeder services to a high-capacity node and concentrated centre.
Any of these may be appropriate, in the right land use-transport context. But they are not always unquestionably “good”, and we can’t expect the land forms suitable for one transport concept to be compatible with another, or vice versa. If the form of development is not matched to the transport facilities available, then it can become non-functional and make transport problems worse, not better.
Think about the difference between Metro systems and trams (streetcars), for example. Trams have a limited and quite specific land use “imprint”, and cannot be expected to service high-intensity point developments as well as their normal route function. What might be a sensible form of development around a heavy rail station or in an area served by a Metro system will not usually be appropriate on a streetcar route.
The reasons are simple:
- Capacity – a streetcar system offers neither the system and access point capacity, nor the service quality of other rail systems
- “Shape” – a streetcar system is highly suitable for linear development with more uniform patterns of boarding and alighting, but dense development in a limited area requires a “nodal” public transport facility such as a Metro or heavy rail station.
Then there is the need to anticipate trip and traffic activity. Intensification of development will create traffic-related problems if the travel choice behaviour of users of the site is not sufficiently different from present behaviour.
In addition, a large increase in non-residential uses in the area will inevitably attract large amounts of service and delivery traffic, which will be almost totally unaffected by the presence or absence of public transport.
Thus, in summary, a proposal that greatly increased the concentration of mixed uses might not be capable of being serviced adequately by a streetcar system and would consequently result in an over-stretched transport system, excessive traffic in a small area, and a worse street environment.
Traffic impact analyses (which should focus on the impacts of the traffic, not impacts on the traffic) should be conducted and scrutinised carefully. To get the data to do this properly, we need to conduct post-evaluations and monitoring of TODs to find out in what ways, if any, they perform differently to other forms of development.