generally when there's a traffic jam in yellowstone it's because people see a herd of elk or buffalo off in the distance so they're eagerly finding a place to pull over so they can take lots of pictures.
we got stuck in quite a traffic jam on saturday. we were just creeping along for at least an hour. traffic was backed up for miles and i got a real kick out of it when we found the reason. three buffalo were just casually making their way down the road.
i think they were headed to old faithful.