#1 Cause of Frustrating Traffic Jams in Yellowstone are Bison
Every summer pictures and videos hit the internet of the LONG traffic jams in Yellowstone National Park and the cause many of these are 'Bison Jams'.
The visitor numbers in the last few years have been so high that traffic is already a major concern for park officials. Then when you add in up to 5,000 Bison and thousands of other types of wildlife that live in the in the park, don't expect to make it quick trip through the park. The 'Bison Jams' are caused when the parks Bison herds are hanging out around the road and can long as 2 hours.
The summer months are when Bison are mating and things can get a bit crazy. This video from the official Yellowstone National Park Facebook page is of a 'Bison Jam' was caused by two Bison Bulls were duking it out for the love of a woman...definitely a situation you don't want to get in the middle of.
When Bison in the park are grazing near the road, there is nothing you can do about it. It's their house and you're just a visitor. When you head to the park, you can expect sitting in your car for quite some time and often you'll be stopped at more than one 'Bison Jam'.
A professor in Transportation Engineering named Daniel Findley is currently on vacation in Yellowstone and posted his extended stop on his Youtube page. During the six and a half minute video, from Lamar Valley in Yellowstone, you can see they spent lots of time sitting in multiple (what he labels as) "Bison (Traffic) Jams"