HOLY ROLLERS.

In the fall of 1971, two years after the Stonewall Rebellion, sixteen months after Kent State, and a couple of weeks after the prison riots at Attica, a few hundred bicyclists rode down Fifth Avenue and on to City Hall, demonstrating for the institution of dedicated bike lanes and bike racks. They called themselves Bike for a Better City. One rider held a sign that read, "The internal combustion engine is antiquated, obscene, and responsible for more deaths thru pollution and mayhem than even that great curse war." A few taxi-drivers razzed the protesters, and at one point an infiltrator, concerned that there were greater causes in need of pursuing, joined the cyclists' ranks, shouting, "People are being murdered and you protest bicycle lanes!"

Since 2000, according to a certain moral calculus, more than a hundred and twenty New York City bicyclists have been murdered--struck dead by automobiles--and another twenty thousand have been injured, by enemy car doors and steel-fortified taxicab fenders. Three were killed in the course of three weeks in June of this year, including one, Dr. Carl Nacht, who was felled by a police tow truck while riding with his wife along the Hudson River Greenway--an officially sanctioned bike path. Since 2004, about six hundred cyclists have been arrested while participating in monthly political-protest rides known as Critical Mass, most notably during the Republican National Convention, when scores were ensnared in nets, and later imprisoned, and their bikes were confiscated as "evidence."

New York is by no means a bicycle haven, like Copenhagen or Amsterdam, or even San Francisco or Madison, Wisconsin, where cycling, despite hilly terrain, is three times as common as it is here. But a smaller proportion of New York residents own automobiles compared with any large city in the Western world, and the local bicycling movement now includes more than twenty groups, with names like Right of Way, FreeWheels, and Revolution Rickshaws, drawing inspiration from sources as varied as the French Situationist philosopher Guy Debord, the civil-rights leaders John Lewis and Hosea Williams, and the urban sociologist Jane Jacobs. Their aims are at once specific (mandating bike storage at office buildings) and all-encompassing: Revolution Rickshaws, for instance, seeks in effect to create an entire pedal-based economy, offering "eco-responsible execution in people-moving services," "rapid urban cargo transport," and "outdoor marketing promotions," through the use of pedicabs, tricycle rigs capable of carrying a thousand pounds of freight, and towable billboards.

Their nominal constituency, the hundred and twenty thousand New Yorkers who ride bicycles every day, comprises three distinct types--commuters (book editors, say, wearing cargo pants), exercisers (lawyers in spandex), and messengers (streetwise minorities without health care)--whose agendas overlap only loosely. And, as with any growing movement, success has brought about factionalization. Roughly speaking, the bikers range, in their political leanings, from Hugo Chavez to Ned Lamont, and in methodology from anarchist street theatre to wonkish position papers. "I think a lot of people realize that this issue is really central to a lot of the dilemmas facing, you know, humanity right now," Paul Steely White, the executive director of Transportation Alternatives, said recently. "How are we going to deal with less oil? How are we going to make cities more sustainable, more livable?"

Transportation Alternatives, or T.A., represents the movement's big tent, with more than five thousand members, a staff of Ivy League graduates, and numerous allies in city government, whom the staff lobbies to enact bike-friendly legislation and other traffic-reducing measures, like express bus service and congestion pricing. White, who is thirty-six, and boyishly affable, was born into a Mormon family, and didn't discover the pleasures of the bike--"mankind's greatest invention"--until college, in Madison. When he left for graduate school, in Montana, his parents, who were by then living in Illinois, shipped his belongings via UPS, and he rode his Cannondale touring bike fifteen hundred miles. He now owns four bikes, including a beater that he leaves on the street, attached to a lamppost or a parking meter. He has let his driver's license expire.

"There's this perception that we're impeding the natural order of things," White told me, over a beer at the bar beneath the T.A. office, on West Twenty-sixth Street. (His employees are forbidden from storing more than one bike at a time.) "It's, like, 'Get a car. Grow up. Men drive cars.' You're somehow a clown or a kid if you're riding a bicycle." ...