Thanks to many helpful suggestions over the years from my friend and mentor Dr. Richard Katzev, I've come to a better understanding of many of the social-psychology aspects of carsharing and personal transportation choices. Some European research on the idea of "mode choice" (driving one's car or to using public transit, walking or bicycling) as a habit seems to me to give some clues about getting members to join carsharing. The following are some highlights I've selected from a Danish study (in English) "Travel Mode Choice as a Habitual Behavior: A Review of the Literature" by Berit Møller, who is in the Department of Marketing at the Aarhus School of Business.
What is a habit? Habits are automatic responses to a situation which may, over time, become generalized to many situations. Habits are formed through repeated behavior in "supportive" environment which "rewards" the individual (i.e. achieves a goal - saving time, comfort, control, etc.) Habits are formed because they are efficient, that is, they require little mental effort to decide, even in complicated situations. Because they fulfill personal needs it means they can be changed, given the right stimuli.
Forming habits requires a lot of thinking initially. Sometimes the choices are deliberate, usually when the individual perceives big consequences for making a bad choice. Other choices are more spontaneous, if they perceive they have made a similar decision before or because they are under time-constraints. Habits may be applied generally or only to specific situations. The choice of a car for a trip is, for most people, a general one - that is, they choose a car in a variety of travel situations. The more general the situation, the harder the habit is to break because the context for applying the habit is so broad.
There are two ways to break "bad" habits - either disturb the automatic process of the habit in order to evoke some deliberation about the choice or change the context that triggers the habit in some way, or a combination of these. One way is to make individuals more conscious of their choices, such by increasing the their awareness of the consequences of their "bad" behavior; and then get them to set a goal and provide some options to achieve that goal. An example of this are program to motivate people to reduce their CO2 contribution by recording their trips and gas purchases until the new behaviors become more habitual. The other strategy, changing the context, is most likely to be effective when there is a change in the transportation system (a bridge or road closure, for example) or a major change in life status (what I referred to as "trigger event" in an earlier post.
You can download a PDF of this paper here.