Any accessible fire roads in Yellowstone?

down in the Tetons Park is one out of Flagg Ranch campground called Grassy Lake Road...I think it goes all the way across the mountains to Idaho, but up at the top of the pass is a lake. Several vauted toilets and little primitive campsite along the way, so take a picnic lunch.

Then down on the southern end is the Snake River road and it is rough and slow going.