Ted Boyd, whose job involves helping develop the city’s South End into a Brooklynesque neighborhood — Mr. Mauney is opening two stores there, one to sell women’s shoes and another men’s underwear — often rides the bus to work. He decided to drive less after a trip to New York, with its extensive options for mass transit, but admits “it’s a little trickier in Charlotte.” Office wear still stands out on the city buses, and “you get some interesting looks sometimes,” he said, that seem to assume an unpleasant reason for why he isn’t behind the wheel: “Is this a D.U.I.?”

Charlotte, whose success as a financial center has helped its population grow toward 800,000, takes transit seriously, said David Howard, a member of the City Council and chairman of its transportation and planning committee. The city tries to channel growth into manageable areas, he said, by filling in the urban core with new development and encouraging new construction along major transportation corridors, including an expanding rail line. “It didn’t happen by mistake,” he said.

The rail line was projected to reach a ridership of 12,000 people within 7 to 10 years; it hit that level in the first month and a half, he said. President Obama has nominated the city’s mayor, Anthony R. Foxx, to be the next transportation secretary.

The drop-off in driving is already having wide-reaching effects across the country. It means that gasoline taxes, which help finance transportation investment, are bringing in less revenue. The U.S. Pirg report suggests that the nation’s shift in driving trends calls for a change in the things the nation spends that money on. “When dollars are so scarce, we need to be sure we’re not building highways that aren’t really needed — especially if doing so means neglecting repairs of existing highways, and neglecting to build transit projects when transit ridership is soaring,” Mr. Baxandall said

Kenneth Orski, a transportation consultant, offered a skeptical view of the permanence of the driving trend. “When twentysomethings get older and start having kids, they move to the more affordable suburbs in search of more space and better schools — and start driving,” he said.

Robert W. Poole Jr., director of transportation policy for the Reason Foundation, a libertarian research organization, also viewed the new report with a measure of incredulity, calling its conclusions “exaggerated.”