Critical Mass – a monthly gathering in San Francisco normally attended by hundreds of cyclists – is going to be a bit bigger and possibly a bit rowdier on Friday night.

The monthly event, which was inspired by the fight for cyclists’ rights, is celebrating its 20th anniversary tonight. Organizers said they expect upwards of 10,000 cyclists to gather at Justin Herman Plaza around 5:30 p.m. before heading off on their ride.

Obviously, with that many people expected in San Francisco’s streets, police have warned drivers to either stay off the road or to take extra precautions when driving on Friday night.

There is no set route that the bikers are expected to take and it is still unclear exactly how long they will be out on their ride, although it is not expected to be for more than an hour or so.

Photo Credit: sf.streetsblog.org

• Tag: Anniversary, Bicyclists, Critical Mass, Justin Herman Plaza, traffic