City CarShare, which promotes itself as providing the "freedom of driving without the hassles of ownership," is geared toward drivers interested in a more economical, efficient and environmentally-friendly alternative to car ownership. In both the United States and Europe, proponents of car sharing say it's a way to prompt some households to give up ownership of their second cars.

Members of City CarShare, who live throughout the Bay Area, pay a $300 deposit, $30 application fee and a $10-a-month administrative fee. They are free to reserve a car in City CarShare's fleet by the day or the hour, paying $3.50 an hour and 37 cents per mile for gasoline. Maintenance, insurance and gas is covered by member fees. Cars are kept in designated lots and returned to one of those lots after use.

Robert Cervero, a UC Berkeley professor of city and regional planning, is leading a three-year evaluation of the city-sponsored City CarShare program for San Francisco's Department of Transportation and Parking. He is researching the program's effects on travel, car ownership, the environment, parking and even the quality of life in various neighborhoods.

After nine months, according to the report recently released, an estimated 7 percent of that program's approximately 1,000 members were using City CarShare vehicles, compared to 2.2 percent participation at the three-month mark. The program offers 70 gas-powered vehicles such as Volkswagen Beetles, Jettas and Golfs, and 10 electric cars from Ford.

In San Francisco, with its approximately 790,000 residents, almost 494,000 registered vehicles and an estimated 320,000 on-street parking spaces, car sharing has the added bonus of transportation without the hassles of hunting for parking. Lots in San Francisco are scattered from North Beach and the Embarcadero to the South Mission and Glen Park BART.

The UC Berkeley study also found that 21.6 percent of the vehicle miles traveled by members were in the program's fleet of cars, up from 8.1 percent three months after City CarShare's launch in March 2001.

"It's been growing. Early on, the City CarShare program was only catching a small share of the vehicle trips made by its members," said Cervero, who was assisted with the research by graduate students Nina Creedman, Muhammad Pohan, Madhav Pai and Yu-Hsin Tsai.

City CarShare provides its service in San Francisco, Berkeley, Oakland and Palo Alto. The program will open on the UC Berkeley campus, possibly during the spring 2003 semester.

This new access to car share vehicles is stimulating motorized travel for people who previously did not have access to a car. The researchers found that most City CarShare members do not own cars, and many appear to be leasing vehicles in lieu of walking and biking. Car share vehicles are used more for personal business and recreational travel than for routine trips such as going to work or school.

While members are gaining access to a car, a new pattern of car use is developing.

"Consistent with the findings from the near-term survey, car sharing appears to be promoting 'judicious automobility' - people are selectively leasing cars at market rates to meet bona fide travel needs, generally not at congested periods or to places well served by public transit, like downtown," the report said.

"Thus, while the leasing of subcompact cars is providing significant personal benefits in the form of travel-time savings, in general this does not appear to be at the expense of high social-environmental costs."

Researchers examined differences in travel patterns between members and non-members of City CarShare at one month into the program, three months and nine months. As long as the influences of other factors - such as rising gas prices - that occur over time are comparable between the two groups, the difference in travel changes can be attributed to car sharing.

Car sharing was pioneered by environmentalists in Germany and Switzerland as a way to reduce car ownership. The idea has spread to cities in Canada, as well as to U.S. cities such as Seattle, Portland, Boston and Chicago, and to the San Francisco Bay Area.