Tomorrow night's Critical Mass in San Francisco marks the 15th anniversary of the rebellious rolling ride that locally has propelled the bicycle movement into the political mainstream and globally has been copied by hundreds of cities.

What began with four dozen bicyclists riding together up Market Street on Sept. 25, 1992, has turned into a monthly happening that regularly draws thousands of participants pedaling along the streets of San Francisco, at times drawing both praise and scorn.

The monthly Critical Mass rides are part political statement and part roving street festival and now are firmly part of San Francisco's cultural fabric.

Critical Mass has no organized leadership. The rides are promoted by word of mouth and over the Internet. The only constant is that they are held the last Friday of the month and start around 6 p.m. at Justin Herman (more...)