Frequently Asked Questions: Winter Use

Do winter use regulations effectively protect park resources?

Recent studies on winter use indicate park resources are in very good condition. Research shows that snowmobiles and snowcoaches contribute similarly to the impacts of winter use. The perception that snowmobiles contribute to the vast majority of observed effects, and that those effects would greatly diminish by limiting travel to snowcoaches only, is not supported. When managed, both modes of transportation provide opportunities for visitors to enjoy the park. Each can offer different experiences for visitors, just as cross-country skiing, snowshoeing, and walking offer different opportunities for visitors to enjoy the park in the winter.


The impact of oversnow vehicles (OSV) on wildlife is a key issue in winter use policies. OSVs are required to stay on groomed roads, but the roads are often situated where wildlife may concentrate in winter. Research indicates that disturbance by winter visitors is not a primary influence on the distribution, movements, or population size and composition of bison, trumpeter swans, elk, coyotes, and bald eagles.

Monitoring OSV use in Yellowstone shows that nearly all OSV users remain on groomed roads and behave appropriately toward wildlife, rarely approaching unless animals are on or adjacent to the road. In most of 7,603 encounters observed between people on OSVs and wildlife, the animals either had no apparent response or looked and then resumed what they were previously doing.

Road grooming does not increase bison migration out of the park. Data on bison road use and off-road travel collected from 1997 to 2005 found bison on the road less often from December to April when the roads were groomed than during the rest of the year, and no evidence that bison preferentially used groomed roads during winter.

Compared to similar studies done in other places, the relatively low intensity of wildlife responses in Yellowstone suggests that because the encounters near roads are predictable and apparently not harmful to the animals, some habituation to OSVs and associated human activities may be occurring.

Making all visitors use a guide has nearly eliminated wildlife harassment. Guides enforce proper touring behaviors, such as passing wildlife on or near roads without harassment and ensuring that wildlife do not obtain human food. Monitoring indicates that snowcoaches have a slightly higher probability of disturbing wildlife than do snowmobiles.

Air quality

Winter air quality in Yellowstone depends primarily on proximity to roads, parking areas, employee housing, and visitor lodging. Although visitation is far lower in the winter than in the summer, OSVs produce more emissions. Prolonged exposure to air pollutants such as carbon monoxide (CO), fine particulate matter (PM <2.5 micrometers), and hydrocarbons can pose health risks.

Levels of carbon monoxide and particulates fell dramatically after 2002 with conversion to BAT snowmobiles and reduced OSV numbers. Hydrocarbon and air toxic concentrations are also no longer a concern, with the possible exception of formaldehyde and benzene levels, which are being closely monitored. Carbon monoxide and particulate matter are monitored at the West Entrance and Old Faithful, where OSVs are most concentrated. BAT snowmobiles and snowcoaches produce a similar amount of air pollution on a per passenger basis. Under the Clean Air Act Amendments of 1977, Yellowstone is one of 156 national parks and wilderness areas that are designated Class I airsheds, requiring the most stringent protection.


Noise levels have also fallen somewhat with the conversion to BAT snowmobiles, mandatory commercial guiding, and limited numbers of snowmobiles. Although snowmobiles and snowcoaches are commonly heard during certain periods of the day, their noise is absent during other times—even in developed areas like Old Faithful and along busy corridors like the West Entrance Road.

Oversnow vehicles are audible 61% of the day at Old Faithful and 51% of the day at Madison Junction, per the 2010–2011 monitoring report, down from 67 and 54%, respectively. (National Park Service vehicles account for approximately one-fourth of this noise.) The BAT requirements for snowcoaches, which will be implemented in 2016, will reduce noise even more. Snowcoaches account for 94% of the loud oversnow vehicles. Guided snowmobile groups and snowcoaches contribute nearly equally to the percentage of time oversnow vehicles are heard.


With guiding has come a 50% reduction of law enforcement incidents, even when accounting for the drop in visitation. Arrests have virtually disappeared. Calls for medical assistance are the only statistic that has increased since the conversion to mandatory guiding.


Last updated: November 17, 2017

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Yellowstone National Park, WY 82190-0168



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