SAN FRANCISCO (Map, News) - The first Critical Mass after a confrontation between motorists and bicyclists will take the streets tonight, including some old-timer cyclists who plan to come out strong to repair the integrity of the event.

The City is planning to double the number of police supervising the ride from 20 to 40 and is deploying officers on bicycles for the first time. Other officers will be on motorcycles and dirt bikes.

The monthly bicycle ride, which has no predetermined route, is expected to draw more participants than usual because of good weather and increased publicity.

Last month’s ride ended with a cyclist throwing a bike through a Peninsula family’s car window, putting Critical Mass in the spotlight and creating tension between drivers and The City’s bicycling community.

For 15 years, hundreds of bicyclists have been gathering for Critical Mass at Justin Herman Plaza on the last Friday of each month before heading out into The City for a three-hour ride with no final destination.

The rides, which have no organized leadership, are supposed to be an occasional night of celebration for bicyclists to flip the traffic experience by becoming the dominant mode of transit on the road. They are, however, often perceived as unruly crowds who run red lights, taunt drivers and block commuter traffic.

Last month’s incident had people criticizing Mayor Gavin Newsom for allowing the rides to occur. Newsom said he would not attempt to dissolve the events, as former Mayor Willie Brown did in the late 1990s, and asked the bicycle community to self-regulate.

Tonight, some veteran Critical Mass riders plan to do just that. A flier will be distributed with basic rules for the ride, which include stopping at red lights and sometimes green lights for safety, allowing trapped drivers to pass through and attempting to defuse any bad behavior.

“If someone is acting badly, grab some fellow riders and tell them: ‘We don’t approve.’ Work together to de-escalate,” the flier states.

Jon Winston, who has been participating in Critical Mass since the beginning in 1992, said he usually intervenes when bicyclists attempt to cross a red light. He will also alert other cyclists to clear the road when there is an emergency vehicle that needs to pass.

“It’s a community. If [Critical Mass] were to fail for some reason, it would be a shame because it has held us together,” Winston said.

The San Francisco Bicycle Coalition, which does not organize or control Critical Mass, sent out an e-mail to about 10,000 people reminding them to be courteous on tonight’s ride.

arocha@examiner.com