
Originally posted by
Cismontane
Obviously, large city regions aren't going to be walkable, but are they transitable? Much of the Socal and San Diego evidence shows that if you restrict parking at the destination, people start taking transit a lot more (and developers are a lot happier, since they don't have to provide as much land for low-yielding surface or, worse, structured parking).
The other factor to consider for Socal and San Diego is the relative cost of driving or using transit. At any given relative cost ratio between the two modes the modal share seems to be largely stable (only availability and cost of destination parking seems to reliably control it), but at around $4.00-$4.50 a gallon cost of gas, transit boardings in San Diego - where the morphology makes transit viable in much of the city - start going bonkers. In the two periods in the last decade that gas stayed above $4.00-$4.50/gallon for sustained periods, you saw radical swings in MTS boardings of up to 40% across the system and sometimes 2 or 3 times at specific transit-rich and TOD-planned stops.
This tells you two things: people will use available, convenient and well-designed transit options at or above certain affordability thresholds. Unfortunately, the corollary to this statement also holds: mere accessibility to transit or transit-friendly urban design and planning does not in and of itself guarantee transit use in the absence of an economic necessity (or exigent trigger). Design can enable the capacity for modal shift, but it cannot actually, in and of itself, dictate modal shift.
In fact, it appears that the choice to live in a TOD doesn't actually involve making a commitment to use transit but rather it entails (among many other factors) the purchase of an option by the new TOD resident to enable his or her use of transit in the event certain exigent circumstances occur (triggers such as unavailable destination parking, car breakdowns and servicing, health-related issues, or spikes in the price of oil). Mathematically speaking, this suggests a very very different model than the deterministic model of behavior pushed by the Smargrowth/New Urbanism crowd... which is that the benefit of transit-oriented development is principally option value, not behavioral. This makes all the difference in the world in terms of what urban design and transportation planning decisions one makes and at what threshold levels.
For PI, I suggest taking a look at data on the income elasticity of transit use in Socal vs San Diego vs San Jose. Transit use in LA is somewhat higher a percentage of total trips in Socal (LA in particular) than it is in San Diego but not so if you control for income. Controlled for income, transit use in LA and San Jose is somewhat lower than it is in San Diego despite your (fallacious IMO) argument that LA is more transit-rich. I suspect this has alot to do with what destinations in San Diego are actually served by transit and the greater frequency of transit friendly morphology, but who knows. My point here is that the evidence is far from clear that simply building more transit results in higher transit modal share with any degree of predictability.