Can they really do this without just banning all bicycles? In my mind there is nothing special about an event like this: it's just a large number of cyclists presumably legally using the roads as they ride through the county. As far as I know, it's not like a race where they would be arranging to close the roads, have police block intersections, etc.

So how can they identify this specific "event" and prevent the bicyclists from using the roads?