Winter Use Management


The National Park Service (NPS) mission is a dual mandate: preserve Yellowstone’s resources and make the park available and accessible for enjoyment and appreciation. The ways in which visitors access Yellowstone in winter can affect the park’s plants, animals, and wild character in ways more profound—and potentially more damaging–than at other times of the year. To meet its mission, the NPS has worked carefully to develop a long-term plan for winter use in Yellowstone that both protects the park’s resources and provides outstanding opportunities “for the benefit and enjoyment of the people.”

For years, the National Park Service managed the park in winter with interim management plans in the face of repeated courtroom challenges over snowmobiles and other winter operations. The final rule, published in October 2013, established long-term management of winter use in Yellowstone and concluded more than 15 years of planning efforts and litigation.

Bombardiers make their way through the rocky formation called the Hoodoos on the way to Mammoth.

History of the Debate

Winter use planning is one of the most contentious issues for park managers and visitors with the debate spanning more than 80 years.

Snowmobiles and a snowcoach line up as they pass a small herd of bison on the road.

Winter Use Planning and Litigation

Learn more about the long history of winter use planning and litigation in the park.


Management by “Transportation Events”

In 2012 the NPS released a draft Supplemental EIS, the seventh environmental document since 2000. This document introduced the idea of managing oversnow vehicles by “transportation events.” Recognizing that a group of snowmobiles traveling together is comparable to a snowcoach in terms of impacts, a transportation event is defined as a group of up to 10 snowmobiles, averaging 7 seasonally, or 1 snowcoach. As OSVs meet stricter air and noise emission standards, group size can increase from a seasonal average of 7 to 8 snowmobiles and from 1 snowcoach to an average of 1.5 across the season. Previous management alternatives were based on managing by absolute numbers of OSVs. Through analysis of monitoring data and computer simulations, the park discovered that by packaging traffic into transportation events (i.e., groups) and limiting the total number of transportation events allowed access into the park each day, the park is able to lessen disturbances to wildlife and improve natural soundscape conditions, in addition to allowing more visitors to see the park in winter. Based on monitoring data, the NPS demonstrated that snowmobile and snowcoach transportation events have comparable impacts on Yellowstone’s resources and values.

In February 2013, the NPS published a final Winter Use Plan/Supplemental EIS to guide the future of winter use in Yellowstone National Park with management by transportation events as the preferred alternative. A proposed rule was published in the Federal Register in April 2013 and the Record of Decision, which officially concludes the SEIS process by selecting management by transportation events as the final alternative, was signed in August 2013.


Frequently Asked Question

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.


A Final Rule for Winter Use in Yellowstone

National Park Service Regulation 36 CFR 2.18 prohibits snowmobile use in national parks when there is no specific rule authorizing their use. This is known as the “closed unless open rule”—without a specific rule, oversnow vehicles would be prohibited from entering Yellowstone.

The final Rule authorizing OSV use in Yellowstone was published in the Federal Register on October 23, 2013 and was based upon the environmental analyses contained within the 2013 SEIS and Record of Decision. The final Rule provides mechanisms to make the park cleaner and quieter than previously authorized; provides greater flexibility for OSV commercial tour operators; rewards new oversnow technologies; allows for increases in public visitation. The specific parameters established by the final Rule for winter use in Yellowstone are

  • Up to 110 daily transportation events.
  • 46 reserved for commercially guided snowmobiles.
  • 4 reserved for non-commercially guided snowmobiles.
  • No less than 60 events reserved for snowcoaches.
  • New "best available technology" (New BAT) is required for snowmobiles by December 2015. Under New BAT, snowmobile transportation events can be up to 10 snowmobiles in a group, with group size averaging 7 each winter.
  • BAT is required for all snowcoaches by December 2016, sooner for newer models.
  • Voluntary "Enhanced BAT" (E-BAT) certification will allow commercial tour operators to increase the average numbers of snowmobiles in their groups from 7 to 8 and snowcoaches from 1 to 1.5 across the season.
  • One non-commercially guided group of up to five snowmobiles is permitted to enter through each of the four park entrances every day.
  • OSVs may continue to use Sylvan Pass; however, the pass may be closed at any time due to avalanche danger or mitigation efforts.
  • Park managers are collaborating with the public by implementing an Adaptive Management Program, which will combine science with public input, to ensure that OSV use impacts stay within limits predicted in the final Plan/SEIS.
A line of snowmobiles spread out on a mountain road
Under the final Rule, OSVs are permitted on Sylvan Pass unless closed for safety reasons.


Adaptive Management Program

The final Rule authorizes an adaptive management program to inform and improve winter use management. Adaptive management is a three-step process: Management, monitoring, and evaluation improve resource protection by blending science and public engagement. It enables natural resource managers to acknowledge uncertainties in the management of natural systems and respond to changing conditions while working with the public and interested stakeholders. Collaborative adaptive management, the approach Yellowstone is taking, emphasizes joint learning and an active partnership between managers, scientists, and other stakeholders, including the public.

The objectives of the program are to

  • Evaluate the impacts of OSV use and help managers implement actions that keep impacts within the range predicted under the final Plan/SEIS.
  • Gather additional data to compare impacts from a group of snowmobiles versus a snowcoach.
  • Reduce impacts on park resources after implementation of the final Rule by gathering additional data on the overall social and ecological impacts of winter use.

To meet these objectives, the NPS has collaborated with the public and other partners to develop a long-term, sustainable adaptive management plan for winter use in Yellowstone National Park. This plan outlines a process for public engagement and for prioritizing indicators to address scientific uncertainty and monitor resources of interest. NPS staff released the final adaptive management plan for winter use to the public in December 2016. Public input is included through participation in the Adaptive Management Team and the Adaptive Management Working Group. Meetings are also held throughout the region and have been available remotely via webinar.


Adaptive Management Team

The winter use Adaptive Management Team is the broader public engagement body that encompasses all working groups, and will provide feedback on the overall implementation of the Adaptive Management Program, including Adaptive Management Plan drafts. The Team will focus on the Adaptive Management Program in its entirety, and will meet regularly to coordinate across impact topics, and to provide feedback to the NPS on Adaptive Management Program operations. The team will also discuss the results of monitoring, how those results are related to the impacts that were described in the final Plan/SEIS, and, if warranted, discuss potential, adaptive changes that may be considered by the NPS. The team is composed of the Adaptive Management Program Coordinator, all working group leads, working group participants and other interested parties. E-mail us to join the team.


Adaptive Management Program Working Groups

The NPS is asking for feedback from working groups, made up of interested stakeholders and citizens, to develop a long-term and sustainable winter use Adaptive Management Plan (AMP), which will guide the park's future data collection on the impacts of winter use. Working groups are sub-groups of the larger adaptive management team, which meets to discuss ideas across topics and provide feedback on the overall AMP process.

The working groups will focus on five impact topics: wildlife, air quality and soundscape, human dimensions, operations and technology and the non-commercially guided snowmobile access program. Each working group will develop a monitoring strategy for its impact topic in coordination with a National Park Service subject-matter expert. Specifically, working groups are tasked with providing feedback on what resource or impact questions should be monitored to address key scientific uncertainties about their impact topic, and on how to design a fiscally sustainable, efficient and feasible monitoring strategy to achieve key monitoring objectives going forward. Park managers will then use the results of winter use monitoring and stakeholder input to make decisions that best protect park resources and the visitor experience.

The Wildlife Working Group will make recommendations to the NPS on the design of an updated monitoring strategy that measures and evaluates the impacts of winter use on the park's wildlife species, including bison, trumpeter swans, elk, lynx, wolverines, gray wolves, and bald eagles to ensure winter wildlife ecology is not disrupted going forward. This group will also provide feedback to the NPS on current and future results of wildlife monitoring and research, and on adaptive management actions that may be implemented in the future as part of the new Adaptive Management Plan. NPS Lead: Brian Teets (307-344-2653).
The Soundscape and Air Quality Working Group will make recommendations to the NPS on the design of an updated monitoring strategy that measures and evaluates the impacts of oversnow vehicle use on the park's natural soundscape and on the park's air quality to ensure a cleaner and quieter park, and compliance with the new winter use sound and air emissions requirements. NPS Lead: Ann Rodman (307-344-2216)
The Human Dimensions Working Group will make recommendations to the NPS on the design of an updated monitoring strategy that 1) measures and evaluates the impacts of winter use on the visitor experience, and other relevant publics, and 2) assesses changes in winter visitation under the new winter use plan and how such changes impact park resources. NPS Lead: Ryan Atwell (307-344-2627).
The Operations and Technology Working Group will make recommendations to the NPS on the design of an updated monitoring strategy that measures and evaluates how winter use operations, under the transportation event concept, and oversnow vehicle technologies can be improved or modified to create a cleaner and quieter park experience, to facilitate cleaner-running vehicles and to generally reduce impacts to park resources. NPS Lead: Christina White (307-344-2320).
The Non-commercially Guided Snowmobile Access Program permits people to snowmobile in Yellowstone without the presence of a commercial guide. Up to four non-commercially guided groups are allowed to enter the park daily: one at each oversnow entrance. NPS Lead: Ivan Kowski (307-344-2627).

Source: Data Store Collection 7696. To search for additional information, visit the Data Store.

A snowcoach is loaded up with skis at Old Faithful for a day of cross-country skiing.

Winter Use Management Archive

Read the various winter use management and planning documents.

Bison walk single-file on a path through snow.

Winter Ecology

Winter in Yellowstone is a place of magic and vulnerability.

Ranger wearing a yellow safety vest talks with another ranger while standing on a bridge.


Review laws and policies, meet park managers, and examine projects and budgets.

Last updated: January 13, 2023

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