Snow coach used in Yellowstone

The attached picture is from 2016. Since the basic units have been used for some time now, I expect them not to have change. What probably has changed is that the lead vehicle in the photo has the track units they'd used for many years, but they are slow and noisy. Not easily seen on the second vehicle is that they were experimenting with large, low-pressure tires which I believe they are now using. Much quieter and somewhat faster.

AlanS: interesting about the vehicle sliding off the road. In 3 Winter trips in Yellowstone which were all-tracked, all-tracked & then the mix, we never saw a tracked vehicle go off the road. Maybe the higher speed possible with the wheeled vehicles isn't an entirely good thing.