They are participating in the "Low-Car Diet," a Zipcar promotion to decrease carbon emissions and get people in better physical shape.
Most of those taking part are employees of Virgance, a company that promotes alternative energy sources and activism campaigns.
Joining the campaign was a "no-brainer," Vigrance spokesman Rahul Prakash said. "We want to promote social change on a small and large scale."
Prakash himself will go car-less for a month; however, he lives in San Francisco and is used to walking from his home on Telegraph Hill to his office in South Park, so he won't notice much of a difference, he said.
Wade Crowfoot, the city's director of climate protection initiatives, also made the commitment. He said the project moves the city one step closer to reaching its goal of reducing greenhouse gas emissions by 20 percent by 2012.
The biggest challenge may be for people like Oakland resident Laura Teng, 27, who works at Levi Strauss and Co. in San Francisco and uses her car regularly.
Teng said she found out about the "Low Car Diet" online and decided to join the team "just to do the right thing."
She said taking BART to and from work won't be a problem, but grocery shopping and calculating traveling times will.
One woman participating in the challenge, who declined to give her name, was telling her friends at the news conference how awkward it could be if she were to go on a date and then had to walk home.
All of the participants still have access to their cars for emergencies, and are allowed to move them to avoid racking up parking tickets. They have been given free BART tickets, San Francisco Municipal Railway passes and access to a Zipcar.
Michael Uribe, general manager of Zipcar, said the company will throw a small party at the end of the 30 days to hear the stories of how people managed.
"I think there will be some good stories," Uribe said. "It's going to change people's lives."