SAN FRANCISCO -- Thousands of cyclists took to the streets of San Francisco on Friday to celebrate 20 years of Critical Mass monthly bike rides through the city.
Critical Mass began in San Francisco on the last Friday of September in 1992. The tradition has continued with a monthly bike ride during the Friday evening commute and has since spread to cities worldwide.
Ride spokesman Chris Carlsson representatives from all over the world came to San Francisco for the anniversary ride, including Critical Mass participants from Brazil, Italy, France, Germany, Japan, Peru and Argentina.
The riders pedaled for miles through the city, snarling traffic and causing huge traffic jams.
"Tonight's ride is super special because it's a birthday ride," Carlsson said.
Organizers say Critical Mass is not only a time to enjoy urban spaces via bicycle, but also to "challenge the use of city streets and the domination of cars and oil in our transportation system."
Several anniversary events, including a film screening and a book release party, were held around the city this week leading up to Friday 6 p.m. ride starting at Justin Herman Plaza at the foot of Market Street.
Motorists are advised to expect delays near the downtown area, but the exact route the bicyclists will take is unplanned, San Francisco Municipal Transportation Agency spokesman Paul Rose said.
"How it's goes on the ride remains to be seen," Carlsson said. Many riders peel off from the main group throughout the ride.
He said for tonight's 20th anniversary ride, cyclists are trying to do a loop along the waterfront then head into the downtown area and then wind through the city.
A special "Kidical Mass" contingent is set to take part in the ride, as well as a women's contingent organized by a female cycling group, "A Girl and Her Bike."
The anniversary celebrations will continue throughout the weekend including a Sunday 1 p.m. "Farewell Bike Ride" leaving from 518 Valencia St. to head to a party at Ocean Beach.
For more information about Critical Mass and its anniversary events visit http://www.sfcriticalmass.org/20th-anniversary/calendar-of-events.