Maybe it was the eve of a new year. Maybe it was the Champagne. Maybe it was simply the right time. Whatever it was, Adam Greenfield of San Francisco made a resolution at a party on Dec. 31, 2008: He would not drive, or ride, in an automobile for all of 2009. This futuristic experiment fit in with Greenfield's lifestyle. A 29-year-old single guy who makes community films for City Hall, he was already commuting from the Inner Sunset mainly by bicycle. And he already believed that we're approaching a time in which oil will be so scarce, or expensive, that few of us will be able to power our cars or have access to foods grown from afar.