Returning students at Carnegie Mellon University have a new transportation option available to them. Zipcar, the world's largest car-sharing company, is coming to campus.

The Cambridge, Mass.-based company hopes to exploit a gap left open by traditional car-rental companies, which historically have either refused to rent to anyone under the age of 21, or charged a hefty premium for doing so.

Zipcar, founded in 1999, entered the college market in 2004, when it placed vehicles on the campus of the University of North Carolina. Carnegie Mellon is one of 10 to 15 new schools that it will serve this year, bringing its total to around 40.

President and Chief Executive Officer Scott Griffith described the company's partnerships with colleges and universities as symbiotic -- they afford the company the opportunity to build its brand with young people, while the schools benefit from having fewer vehicles on campus.

"Colleges always have problems with too much congestion in the communities they operate in," he said.

For Mr. Griffith, the move represents something of a homecoming since he is a native of Murrysville, and graduated from CMU with a degree in engineering in 1981.

Zipcar was founded by a pair of friends, Robin Chase and Antaj Danielson, who were inspired by the car sharing that they observed during a trip to Europe. Since then, the company has grown to 24 cities throughout North America and the United Kingdom. Their 3,650-vehicle fleet includes hybrids, pickups, compacts, sedans and sports cars shared by 130,000 members who typically pay an annual fee of $50 to participate. For college students, the annual fee drops to $35.

The company's partnership with CMU will begin modestly, with two cars on campus: a Mazda 3 sedan and a Toyota Prius hybrid.

Zipcar members can reserve a car either by Internet, at www.zipcar.com, or by phone, for a period of hours or days. When they go to pick up the car at a designated location, waving a membership card over the windshield unlocks the doors, allowing the member to retrieve the car key inside. At the end of the reserved time, the member returns the car to its parking spot and replaces the key.

The fee for the service starts at $7 per hour, which includes gas, insurance, 180 free miles per day, parking, maintenance and emergency service.

Zipcar is the second car-sharing service to enter the Pittsburgh market in less than four months. In May, Seattle-based Flexcar arrived in Pittsburgh with a fleet of 20 vehicles, which are parked in locations throughout Downtown and Oakland.