This is a video demonstrating how race organizers and police allow crowds to cross the race path during the Boston Marathon. A pretty clever solution. Personally, I would have suggested building ariel walkways, but that's just me and I own a construction company that's notorious for low bidding on government contracts, then following up with some of the shoddiest work you've ever seen, and me on the lam in Mexico. *phone rings, immediately starts climbing out window* No estoy aquí.
Keep going for the video.