9/27: 5-6,000 people rode through the streets of San Francisco celebrating the 10th Anniversary of Critical Mass during Friday's rush hour - while cars honked but remained motionless at dozens of intersections. A monthly grassroots event, Critical Mass is decentralized to the point that bicyclists spontaneously organize themselves into groups and ride off throughout the city with the purpose of reclaiming public space for bicycles. The Mass was split into several still-critical masses by traffic cops, only to reconverge in riotous music and merrymaking at City Hall and Dolores Park. The Bike for Colombia sound system called for global justice and an end to Bush's "Plan Colombia" oil war which is terrorizing that South American nation. SFPD reported 6-12 arrests and 3 injuries.

Though vilified by some motorists, Critical Mass bicyclists have for 10 years brought about positive social change in the form of bike-friendly laws -- and had fun while doing it. "I'm here to celebrate community coming together in civil disobedience, and to mess things up a little bit!," said Robin Honan of San Francisco, who wore a pink birthday cake on her head. Critical Mass, which began in San Francisco, takes place the last Friday of every month and is now celebrated in over 300 cities worldwide. The 10th anniversary celebration coincided with San Francisco's first annual Car-Free Day. Photos