From ArborWiki

Car pooling, or ride sharing, involves connecting drivers who are willing to take passengers with people who need a ride. Ann Arbor resources include,

• AATA's [RideShare carpool matching service, intended for commuter use. Note that this service only serves commuters with work destinations within Washtenaw County, and not County residents who commute elsewhere.
• RideNow is a more ad hoc service / study out of the School of Information.

Car sharing is a setup by which multiple people share use of (or "have shares in") a car or pool of cars. This can be done as a for-profit business, as a non-profit cooperative, or as an informal arrangement. The idea behind it is that fixed costs, such as purchase of the car, insurance, and parking permits, can be amortized across a group of people by making more intensive/efficient use of the car's time.

The Ann Arbor group [A2C3], or Ann Arbor Community Car Cooperative]], has had a car on the road for over a year. Being volunteer-run by extremely busy people who are involved in many other things, though, they're hardly the slickest group around, and have a fairly low profile.

Known Detroit car sharing organizations include (both for-profit)

• Motor City Car Share
• ViaCar (Pronunciation indicated by their slogan, "Why buy a car when you can ViaCar?")