SAN FRANCISCO -- Kyle Minor doesn't usually need a car in his bustling neighborhood, where it's a cinch to find a bus, cab or train. But mass transit doesn't always cut it for those grocery runs and weekend road trips to Napa Valley.

So Minor signed up for a car-sharing service, joining thousands of Americans who need a set of wheels from time to time but are leery about shelling out money for car payments, fuel and insurance.

"I think it's fantastic," said Minor, who works in the city's opera box office and has gone carless for four years. "We've been extremely happy and we've used the cars to go all over the place."

Car sharing services operate in several cities, including New York, San Francisco, Washington, Boston, Seattle, Chicago and Boulder, Colo. The concept has grown in popularity, prompting car sharing groups to add more vehicles and expand into new cities. They've gotten help from federal transportation grants, seed money from eager communities and city-subsidized parking spots.

$30 to join

Members of City Carshare in San Francisco pay $30 to join and put down a $300 deposit in case of damage to the car. When they need to take a drive, they spend $3.50 per hour -- no more than $35 per day -- plus 37 cents per mile. The cost of gas is included.

Members receive an electronic key card and a gas card. When they need a car, they reserve time slots online or over the phone, and walk or use mass transit to get to locations where the station wagons, Volkswagen Beetles and sedans are parked. The key card gets members into cars at the locations and times they requested.

The idea may be profitable, too. Robin Chase, chief executive of Cambridge, Mass.-based Zipcar Inc., said her company broke even after three years and has expanded from Boston to New York and Washington, with 5,000 members sharing 136 cars.

Chase said she was inspired to launch the service when she realized it was exactly what she needed -- to have an extra car to run errands without the hassles of owning a vehicle.

San Francisco's City Carshare, a nonprofit service, began with 12 lime-green Beetles last spring, expecting 500 members. Now there are 45 cars and 1,400 members, some of them across the bay in Oakland and Berkeley, said Annie Bourdon, the group's outreach coordinator. The cars, which are available 24 hours a day, seven days a week, are currently used about seven to nine hours a day, according to Carshare.

Bourdon credits the enthusiasm of customers like Barbara King, a registered nurse from London staying with family in San Francisco. Buying, leasing or renting a car for three months seemed financially impractical, King said, so she turned to car sharing.

"I think that if I lived in San Francisco again I would consider doing this rather than owning a car," King said after she crossed the Golden Gate Bridge.

No-cost insurance

City Carshare cleans and maintains the cars and provides full insurance coverage -- which Bourdon said tops $400 per month per car, making it the organization's largest expense.

Officials at car sharing groups say their services aren't meant to be substitutes for buses, trains and other forms of mass transit.

"Our mission is to provide a convenient and affordable alternative to car ownership," Bourdon said. "Urban space is so sacred and it's a shame it all goes to parking."

Car sharing isn't for everyone, the groups say. Most reject customers who have had been arrested for drunk or reckless driving, or have had several moving violations. Members are expected to keep the cars in good shape and to return them with gas in the tank for the next driver.