This is an interesting concept created by a group at M.I.T. The basic idea is that commuters need a way to get from the airport, bus station or train depot to continue thier journey. The concept is similiar to one of the rentable luggage racks at the airport or a shopping cart kind of idea as they stack and can get several of them in a single parking spot.
Here's the full article http://www.technologyreview.com/Infotech/19651/