Another way to run it is to make everyone responsible for staying with the rider directly behind them that they see in their mirror. If the rider behind stops, then the rider in front stops at the first safe place. And so on up the line. They stay put until the group leader (or someone else that is designated to do so, maybe the sweep rider) circles back and collects all his ducklings. No problem if the group gets separated by a red light--the front section will pull over and wait. The goal is to get to the destination more or less together and have fun doing it. Not to maintain a parade-like formation. Not to ride at a level that makes anyone uncomfortable. Never ever to do anything illegal or unsafe.