Car sharing revs up with backing from Detroit heavyweights

Wheelz launch on college campuses for a bunch of reasons. Students tend to be tech-savvy, early adopters. They tend to trust their classmates. They think about consumption in a different way than their parents do. Most of all, some kids have cars and others want them. "At every college in America, there's supply and demand,"  MIller said. “The college and university is an ideal place to start -- the key words being place to start, not finish.”

Boston-based RelayRides, meanwhile, is expanding from Boston and San Francisco, where it currently offers cars, to the rest of the country, with an assist from General Motors. GM has about 6 million OnStar subscribers, who will be offered the chance to rent through RelayRides. GM will get a cut of the rentals, as Steve Girsky, the company's vice chairman, told the LA Times:

"Urban mobility solutions are a vital building block of the future success of GM," Girsky said. "Peer to peer concepts such as RelayRides in combination with OnStar's technology delivers against this target. We could stand on the sidelines and watch or we could choose to participate and try to make it into a favorable business model, which in this particular case, we have."

All of this is unproven, of course, and it bumps up the very American idea of owning your own wheels. Then again, we're in a sluggish economy -- which makes sharing attractive -- and the environmental benefits of car sharing are obvious.

Car sharing is one of many businesses made possible by the overlap of social media and sustainability, which will be one of the topics next month at FORTUNE's Brainstorm Green conference, which I co-chair. I'm pleased that Jeff Miller of Wheelz has agreed to speak. On our agenda, too: Ford CEO Alan Mulally and and Scott Griffith, CEO of Zipcar. It should make for some interesting car talk.

Photo of passing along car keys via; logos courtesy of Wheelz and RelayRides via