[graupel]

Sounds like the way Critical Mass (cycling) rides in Chicago work - with no pre-set route the police join in and make sure no one gets hurt but they can't really push the ride in one direction or another - the 'hive' decides where to go. With 5,000 to 10,000 people it's a pretty huge event/example.

[neilk]

That's not specific to Chicago. All Critical Mass rides work that way.

[cpeterso]

Critical Mass is a good example of how not to gain sympathy for one's cause. Blocking traffic, running red lights, and shouting at or kicking cars of people trying to commute home after a long workday does not endear bicyclists to drivers. In San Francisco, the riders are sometimes known as "Critical Massholes".