And the animals, it doesn't bother them. You let them cross the road. You enjoy them. Such close-up encounters, while thrilling for humans, could pose hazards for the giant animals. In some circumstances the bison appear to just ignore the vehicle.
Snowmobiles make that mandate difficult to fulfill.
Even so, studies show snowmobiles are responsible for most of the air pollution in the park. 55,000 snowmobiles enter the park each year About 55,000 snowmobiles enter the park each winter at the West Yellowstone entrance. When employees working there reported getting sick, the park found high carbon monoxide levels and had to start pumping fresh air into the entrance booths. The pollution levels at the west entrance at times range as high as famously smoggy cities like Denver and Atlanta. It may be hard to believe the small machines could broadly affect the air in Yellowstone, a park bigger than Delaware and Rhode Island combined.