The first Critical Mass ride in Budapest was organised on Car Free Day, September 22, 2004, though it was preceded by at least 50 similar bicycle events initiated either by organisations, groups of bicycle couriers, or other pockets of non-affiliated individuals. The September 2004 ride, however, was significant in that it combined almost every previous organiser into one mass of cycle enthusiasts and concerned citizens. That event drew a surprising 4000 participants. By Earth Day 2005, the number of Critical Mass participants reached 10,000, and doubled again for the September 2005 event, reaching 20,000. On Earth Day 2006 an international record of 32,000 participants was reached, to be topped only by next year’s similar event, with a turnout of 50,000, reaching as many 80,000 by April 2008.
Source: Critical Mass.