San Francisco Bicyclists Pedal Home the Point : Commuters: Once a month, 600 of them crowd Market Street to focus attention on transit priorities.

With the tintinnabulation of 600 bicycle bells, the liberation of Market Street begins.

It’s 5:30 p.m. on the final Friday of the month. In an act of urban anarchic creativity, San Francisco’s beleaguered bicyclists take over the city’s main downtown thoroughfare.

In just under a year, “Critical Mass” has become a full-fledged event: Hundreds of cyclists who commute through the bicycle-unfriendly urban core take a monthly mass ride, banishing cars by sheer numbers.

At 5:40 more and more cyclists are milling at Embarcadero Plaza Park at the base of Market Street. Some wear suits and ties, others neon biker gear. All bear the slightly wary look of people who must share the road with cars.

“No one respects bike space,” says Deirdre Crowley, 28, of San Francisco. “It’s a war. Bicyclists are always the ones who get blamed. But it’s the taxis who pull into bike lanes and stop dead. We end up playing tag with the buses because they drive in the bike lanes.”

Like many of her compatriots, Crowley doesn’t own a car.

A phalanx of police on motorcycles stand ready at the corner. One asks who’s in charge and when the ride will begin.

“No one’s in charge,” several cyclists call back.

The Ride, as it is referred to, is an extremely non-hierarchical event.

“Critical Mass is a monthly organized coincidence. We are all simply riding home . . . together!” writes Chris Carlsson in “Broken Spoke: A Xerocratic Publication for the Love of Bicycles,” distributed during the ride.

“Critical Mass is a public act of self-acknowledgement by bicyclists who are at the cutting edge of challenging the transit priorities of this society,” Carlsson says.

It’s also a gas. For this brief ride there is no fear of being cut off, knocked down or smashed flat. For one hour, the city’s bicyclists join together in the exhilaration of the freedom of the streets.

By 5:50 the crowd has grown to more than 600. Isolated shouts of “Let’s start,” and “Ride,” are heard. The ring of bicycle bells becomes a cacophony. Suddenly, the massed riders spill into the street.

Once again, Critical Mass has been achieved.

Riders break into spontaneous whoops of joy as they pedal up the wide avenue toward Mission Dolores Park a mile to the southwest. Cyclists fill the two right-hand lanes of Market for three full city blocks. At each intersection two or three “corkers” block the cars that try to merge into the river of bikes.

Motorcycle police keep watch over cyclists and drivers.

During the June ride a motorist angry at the delay rammed his car into a “corker” who was holding a sign that read “Thank You for Waiting.”

The woman was knocked to the ground and her bike crushed, according to San Francisco bicycle coordinator Dave Snyder.

A crowd of bikers surrounded the driver’s car and smashed his windows with their bike locks. The woman who was knocked down was charged with malicious nuisance for being in the way, Snyder says.

At least 5,000 people a day commute by bike in San Francisco, Snyder says.

Whether they work for law firms or messenger services, anyone who rides in San Francisco knows the easygoing City by the Bay is anything but when you’re on a bicycle.

“Once I was in Chinatown--it’s the worst,” says 22-year-old Adam Powell, leaning over the handlebars of a 10-speed.

“This guy totally cut me off--first he pushed me into a wall and then he forced me into a parked van. A block later he caught up with me and started yelling at me like I was the one who didn’t have a right to be in the street.”

The famous hills don’t help. And then there’s a hazard unique to the city--the tracks of San Francisco’s picturesque cable cars.

“I’ve seen a lot of people wreck on cable car tracks. It’s so easy to get your tires caught in the grooves and then you’re dead meat,” says Crowley, shaking her helmeted head.

The Critical Mass concept has pedalled off on its own. In Berkeley, an East Bay Critical Mass draws 150 to 200 riders the second Friday of each month.

And in Manhattan, where police say more than 300 bicyclists and pedestrians are killed a year, 150 cyclists ride from Washington Square to Central Park the fourth Thursday of every month.

Drivers should appreciate bicycles because they reduce traffic and make the city easier for everyone to live in, said Vince Mahoney, 32. He has commuted downtown to work by bike for more than 12 years and does not own a car.

“A good day is when people treat you with respect,” he says. “A bad day is when people treat you like you had no business on the road.”