SAN FRANCISCO – Shannon Stairhime and her car split up every morning. She commutes on public transportation to her job in the East Bay while her Toyota Corolla waits on the street for its next driver.

"It used to just sit there and occasionally get tickets," said Stairhime, who rents her car to neighbors for $5 an hour through a new business called RelayRides. "Now I feel like I'm contributing and giving back to the neighborhood."

She's not going to get rich, but the arrangement helps alleviate the guilt of owning a car in an auto-choked city, she said. Noe Corolla, as her car is known, now earns part of its own keep.

It joins Betty, Das Beetle, Agent Orange, The Proton and Castro Vibes, among others, that sit on city streets with signs announcing, "Borrow My Car." Since December, when Relay started in San Francisco, 2,500 people have signed up to rent some 100 available cars.

The company is just one targeting San Francisco as a prime location for a new generation of car sharing. Unlike traditional rental companies or membership-based organizations such as Zipcar that allow renters access to a fleet of autos parked near them, the new enterprises support person-to-person rentals.

Such businesses appeal to people who balk at the expense and hassle of maintaining, insuring and parking a car. In San Francisco, vehicles outnumber spaces, and city figures estimate that snagging an off-street spot costs $10 to $50 a day.

The companies also attract those who believe sharing helps solve social and environmental problems. The idea resonates in the Bay Area, where clothing and food swaps, community gardens and bartering are increasingly popular.

"We see this as part of a trend of collaborative consumption," said Jessica Scorpio, co-founder of Getaround, which has a few hundred members in the Bay Area. "It's a kind of sharing in your neighborhood."

Scorpio and her business partner thought up the idea for Getaround as graduate students at Singularity University, a campus based at NASA Ames in Silicon Valley.

While looking at ways to decrease the number of cars on the planet, they turned to a new model for car sharing, supported by technology that would safely allow people to rent out their own unused cars.

The specifics of how people check out cars and unlock them might vary – Getaround members mostly use a device that unlocks cars with a cell phone, while those with Relay use a coded card – but the companies share a concept. Find a car on the company's website, and go pick it up.

The companies screen cars and drivers, provide insurance and take a cut of the proceeds. Owners set the rates, ranging from $3 to $15 an hour for family sedans, hybrids, sports cars and SUVs. This being the Internet age, renters sometimes review rides online. Car owners have left their CD collections or, in one case, fresh-baked cookies for renters.

"This is a great city for car sharing," said Shelby Clark, a founder of Relay, who rents out his own Mini Cooper.

"The idea is foreign in some places," Clark added. "It's so American to own your own car, but that's shifting."

He got the idea for Relay while trying to rent a car on a nasty day in Boston, where he lived as an MBA student at Harvard.

Walking past parked cars, he kept thinking, "I want to get in that car, or that car," he said. "Why not? They were just sitting there."

Judy van Soldt, an architect who sold her car about five years ago, has rented through Relay about a dozen times. She's borrowed a tiny Smart Car to see what it was like and a larger car to pick up friends from the airport.

"What I like is the money stays local," she said. "I'm not paying Budget rental in Pittsburgh or wherever they are. My neighbors get the money."

Blues musician Gigi Amos, who has used Getaround cars to drive to gigs, was pleasantly surprised when a previous renter returned late, but left her an energy bar as a token apology.

"It seems like people involved with this kind of thing have a certain attitude in general," Amos said. "They're not so stuck on owning things."

Editor's note: This story was changed Aug. 18 to correct the name of Getaround co-founder Jessica Scorpio.

© Copyright The Sacramento Bee. All rights reserved.

Katherine Seligman is a San Francisco-based freelance writer.

• Read more articles by Katherine Seligman