Looks like a significant amount of car use happens just because our car is sitting there, just outside the door, waiting to be used. 

Place an obstacle in the way of getting into your car – in this case, getting oneself to where a share car is located, and suddenly people find they don’t need a car after all – they walk, bike or use public transport.

And of course, owning a car is an expensive hassle in itself…as evidenced by the fact that a fifth of Zipcar members actually sold their own cars after joining the scheme.