I have used mine for quite a few years. It is amazing. I think the charge for driving into Yellowstone is now around $30? When I fish the area, I go in and out of the Park many times.......often the same day. You need a pass each time you enter. The Senior Pass has really saved money for me. Someone might verify the $30 figure???
Or, is a daily pass good all day, even if you exit and return?