Transit and livable streets advocates talk a lot about mode shift: providing incentives for people to choose transit, walking or cycling over driving. What often gets lost in the discussion is that the choice of mode is not one simple choice. It's a lifelong series of choices that overlap and influence each other. I divide these choices into four groups:
Single trips are fairly self-explanatory. I went to Park Slope with my son this past weekend. We took the subway, but I briefly considered taking a taxi or bus. While in Park Slope we walked from one part of the neighborhood to the other, but I contemplated taking a subway, bus or dollar van.
Most of our trips are not decided ad hoc on a daily basis. Instead, we form habits of travel. I usually take the subway to work, but once in a while I'm running late and take a taxi.
Every once in a while we make a major decision that influences our single trip and habit decisions. Usually it has to do with housing location, job location or vehicle ownership; I call it an investment choice. In 1999, living in another city, I acquired a Jeep Cherokee. From then on I drove much more often, and rode my bike and walked less. I don't think I took transit in that town again. In 2000 I moved back to New York City and immediately gave away the SUV, and as you might expect I almost completely stopped driving.
Politically, we can choose to support subsidies of one mode of transportation or another, and we can support taxing one mode more than another.
There are three factors that affect our choice of mode, but each of these four choices is affected by the factors differently:
Can you use this mode? Does it go where you want to go? Can you get back easily? The availability of a mode is the most basic factor; without availability there is nothing.
Is it worth it? Does it get you where you're going faster, cheaper or more comfortably than the other modes you're considering? Which mode provides better value?
Is it exciting? Will it help you leave the boredom and frustration of your current life behind and start a new, liberating experience? This is what Virginia Postrel calls glamour.
Glamour can affect our choices to take a single trip, to invest our time and money in a new place or to lobby the government in support or protest of subsidies. But critically, habits are much more affected by value than by glamour. This makes sense because it's harder to sustain a habit that's built on an escape fantasy, but if you've gone out and bought the new Corvette you had your eye on, from now on you've made it much easier to drive.