Summary: It started with a bike ride in San Francisco on Sept. 25, 1992. About 50 people cycled in a pack along Market Street, hoping to earn some respect from drivers who sometimes ignored them or edged them off the road. They called it the "Commute Clot." Today it's known as Critical Mass, a movement that's spread worldwide. Supporters say it promotes cycling and the rights of bicyclists. But critics say it is illegal, clogs traffic and antagonizes drivers. We talk about Critical Mass' 20th anniversary, and its effects on the city.
