Critical Mass (cycling) 单车临界量
（重定向自Xerocracy）
Critical Mass is a cycling event typically held on the last Friday of every month; its purpose is not usually formalized beyond the direct action of meeting at a set location and time and traveling as a group through city or town streets on bikes.
The event originated in 1992 in San Francisco; by the end of 2003, the event was being held in over 300 cities around the world.