City Councilman Bill Peduto gave up the keys to his black Mini Cooper yesterday, joining 16 others in taking the "low-car diet" that is being promoted by Zipcar in 12 cities nationally.

At a Market Square ceremony, each participant walked to the stage when called and dropped his keys in a box. Each got a free Zipcar membership and, for the next four weeks, $500 worth of Zipcar driving credits and free bus passes. Smaller perks include a week's pass to a South Side health club, free shoe shines at a Downtown shop and a case of vitamin water.

Zipcar is a car-sharing service whose members pay a one-time $25 fee and rent by the hour or the day and pay by the month or year, depending on use. Pittsburgh got the service last year, starting as Flexcar, which merged with Zipcar. It has 40 cars Downtown and in four neighborhoods -- Oakland, Shadyside, Squirrel Hill and Bloomfield.

Jenna Cox, general manager of Zipcar Pittsburgh, said those neighborhoods have the most use. She said she is not permitted to say how many members it has locally. It has 225,000 members nationwide.

Yesterday's participants, most in casual clothes, appeared to be in their 20s and 30s. They sat in a line facing the stage. Mr. Peduto, 43, in suit and tie, seemed to surprise Mayor Luke Ravenstahl, who told the lunchtime crowd he thought Mr. Peduto was there in an official capacity before finding out he was participating.

"Thank you for your leadership on this issue," Mr. Ravenstahl told him. "With gas at $4 a gallon, it's obvious we all need to do more."

One of the city's environmental leaders, Mr. Peduto said another reason for taking this monthlong test is "the dependency thing."

"I feel dependent on my car," he said. "I think you have to prove to yourself you can do your job and live your life without an automobile sitting right outside your door. That's an uncomfortable situation, and I wanted to push myself to see if I could do it."

Jessica McCurdy, 25, his office manager who lives in Shadyside, decided to try it too, "because I drive so little anyway," she said.

Darren Liu, a 34-year-old graduate student at the University of Pittsburgh, said he takes the bus to Oakland from his home in Highland Park, using his 1999 Olds Alero on weekends.

"That's why I think I can do this," he said. "A lot of people think they can get someplace more easily in their car than the bus, but traffic seems to be worse."

Breen Masciotra, 28, a staffer for state Rep. Chelsa Wagner, said she drives her 2003 Ford Focus from home in Mount Washington to work in Brookline, in part because it's less expensive than a $2 bus ride each way.

"But I'd like to drive less," she said. "I like the excuse of driving less. It's one-half mile from my house to the bus stop."

She said planning ahead is the challenge.

Mr. Peduto said he replanned his week.

"Monday and Tuesday, I will ride-share with Dan [Gilman, his assistant]. Wednesday and Thursday, I'll take the bus, and Friday is the bike" that he dusted off and had retuned. For bike day, he said, "I changed all my Friday meetings so they are in my district."

Visiting his mother in Scott and playing hockey on Neville Island are his main car needs, he said.

"It's a little scary," he said, taking a deep breath. "But I think I can do this."