As San Franciscans already know, once a month cyclists from all over the city gather to ride en mass, an event known as Critical Mass. But since tonight is the movement's 20th anniversary, you should expect the roads to be even more clogged than usual with some 10,000 riders coming to celebrate from around the globe.
So what does that mean for you? Leave work early, because the masses will hit critical levels in downtown sometime after 6 p.m. No specific route has been mapped out.
We never thought we'd be saying this, but you're probably better off taking Muni or BART this evening.
The movement, which was started in 1992 by Chris Carlsson and 50 of his closest friends, has crossed the nation and the globe, with most rides being fun and peaceful, aside from the 1997 ride that turned violent.
However, the cops aren't expecting too much trouble tonight, but there will be more police on the streets -- just in case.
"You might be inconvenienced for a few minutes, but it is a rolling event so it will pass by," said Officer Albie Esparza. "Our job is to monitor the event and make sure everyone's rights are protected."
Riders will meet up at Justin Herman Plaza this evening before pedaling off into the night.