The first thing that comes to mind with transit-oriented development, and sometimes the only thing, is proximity to a busy rail station. The term begins with transit for a reason. But of course that's not the only component of effective TOD: density, a mixture of residences and services, walkability, and the general built environment all play key roles. What if some of these other factors proved as important as rail proximity when it came to TOD's sustainable impact?
In other words, what if TOD doesn't rely on the T?
That was the question asked by planner Daniel Chatman of the University of California-Berkeley for a study published in the winter 2013 issue of Journal of the American Planning Association. His answer may come as a bit of a surprise. Chatman found that proximity to rail was not the essential TOD element it's typically thought to be — and, in fact, that it's importance vanished in the face of other factors:
In these data, the lower auto ownership and use in TODs is not from the T (transit), or at least, not from the R (rail), but from lower on- and off-street parking availability; better bus service; smaller and rental housing; more jobs, residents, and stores within walking distance; proximity to downtown; and higher subregional employment density.
Chatman reached his conclusions after analyzing the areas around 10 rail stations in New Jersey. Using self-report household surveys and on-site area observations, Chatman collected information on station proximity, parking availability, and local bus stops and grocery stores. He added Census and general research on housing age, commute time to Manhattan, and population, retail and employment density.
After modeling all the material, Chatman found that transit-oriented development did indeed have a positive impact on several measures of car dependency. When he drilled deeper into what TOD elements were most responsible for this benefit, however, proximity to rail didn't carry its expected weight.
Take car ownership. Chatman found that it was 27 percent lower per capita in new housing near a rail station compared to new housing far from one. But once he controlled for housing type (rented or owned), neighborhood parking, and area bus stops, the significance of the rail station disappeared. Rail proximity was no longer linked to car ownership; instead, the scarcity of off-street parking was a powerful predictor.
Same thing with car commuting and car trips to the grocery store. Before controlling for other variables, Chatman found that each mile away from a rail station increased a household's odds of driving to work by 74 percent. Likewise, before considering the controls, he found more weekly car trips to the store with every mile from the station a household was located.
But in the face of housing type and parking and built environment, the significance of rail once again slipped away. Off-street parking, job density, bus stop prevalence, and distance to Manhattan were stronger links to car commuting. Similarly, supermarkets within a quarter mile of one's home reduced car trips to the store, and scarce neighborhood parking cut them by a quarter.
So transit-oriented development does indeed seem to reduce car use, concludes Chatman, but that benefit may not have as much to do with proximity to a rail station as most people presume. Other factors — from parking to mixed-use development — may have just as valuable a role. On the whole, writes Chatman, the data suggest that rail's role here is an "indirect" one at best.
The results may be a little jarring, but Chatman actually sees them as encouraging. After all, developable area around rail stations is limited. If factors other than rail proximity can be emphasized and still produce decreases in car reliance, then the spirit of TOD can extend far beyond the T, he writes. At the very least, recognizing a potential limited role of rail proximity should remind planners that there's much more to the TOD job:
Current sustainability policies are often quite focused on investing in rail and developing housing near rail stations. ... Such a focus primarily on TODs to reduce greenhouse gases could miss the boat. These results suggest that a better strategy in many urban areas would be to incentivize housing developments of smaller rental units with lower on- and off-street parking availability, in locations with better bus service and higher subregional employment density.
Now it's important to remember that there are many variables in play here and their relationships are all extremely complicated. Until the results are replicated in other areas, and perhaps with a more consummate car use metric like vehicle miles traveled, the finding is probably more intriguing than game-changing. So it may not be time to remove the T from TOD quite yet, but it seems worthwhile to reconsider whether or not it's truly a capital letter.