According to the National Parks Conservation Association, use of snowmobiles outside of Alaska has mostly been concentrated in five units of the park system: Yellowstone National Park, Voyageurs National Park, Rocky Mountain National Park, Pictured Rocks National Lakeshore, and the John D. Rockefeller Memorial Parkway. Snowmobile visits to Yellowstone increased during the 2000-2001 and 2001-2002 winter seasons, peaking at 87,206 in the latter winter. Park Service Policy on Snowmobile Access

Although recreational access by snowmobiles has been permitted in units of the national park system, the Park Service, in the late 1990s, concluded that such use has generally been in violation of Executive Orders 11644 and 11989, issued by Presidents Nixon and Carter respectively. Upon completion of the study, the Clinton Administration promulgated a final rule in January 2001, banning snowmobiles from Yellowstone, Grand Teton, and the Rockefeller Parkway beginning in the winter of 2003-2004, but allowing continued visitor access through the use of "snowcoaches"—guided tour-vans that run on rubber treads. The machines themselves would have been required to achieve a 90% reduction in hydrocarbon emissions and a 70% reduction in carbon monoxide under the 2003 rules. The most recent version, released in February 2008, contains 26 models. (The Wyoming court vacated and remanded the Clinton rules on October 14, 2004.) Snowcoaches are also allowed. The snowmobiles would be required to meet best available technology requirements for emissions and noise, and it would require that snowmobilers be accompanied by commercial guides. On September 15, 2008, Judge Emmett Sullivan of the U.S. District Court for the District of Columbia vacated the plan, finding it "arbitrary and capricious, unsupported by the record, and contrary to law." With the rule vacated, it is unclear what limits will apply in the coming winter season. Clean Air Act and Noise Control Act Regulation

In reversing the Clinton Administration rules on Yellowstone access, the National Park Service set limits on emissions and noise from the snowmobiles that would be allowed in the three Yellowstone area park units. In one hour, a typical snowmobile emits as much hydrocarbon as a 2008 model automobile emits in 54,000 miles of driving. In a day of use, a snowmobile may emit as much hydrocarbon as an automobile emits over its entire lifetime. As noted, the National Park Service promulgated noise standards applicable to snowmobiles entering its three Yellowstone area park units beginning December 17, 2003, under the winter use rule that was vacated; it restated these standards in its Temporary Winter Use Plan that took effect in 2004. On June 1, 2004, the U.S. Court of Appeals for the D.C. In its October 5, 2001 Federal Register notice, which proposed the snowmobile standards, the Agency identified 7 areas in Alaska, Washington, Colorado, Oregon, and Montana that have significant populations of snowmobiles and have failed to attain the air quality standard for CO.
Manufacturers of snowmobiles and other nonroad vehicles note, however, that carbon monoxide concentrations have declined [chiefly as a result of auto emission standards] and that none of the 7 areas identified by the Agency has exceeded the CO standard in recent years, even if they were still formally classified as nonattainment at the time of the proposal. Congress and the NPS have provided a temporary resolution of the Yellowstone access issue since 2004, but the issue is now returning to the limelight, as a federal district court has vacated final regulations for Yellowstone access for a third time. The development of these rules showed that public interest in snowmobile issues remains significant, and that the National Park Service's preferred alternatives for snowmobile access to Yellowstone remain overwhelmingly unpopular. Among those opposed, environmental groups and individuals that want snowmobiles banned from the park form a solid majority.
For at least a decade, the use of snowmobiles in Yellowstone and other national parks has been controversial because of the potential impacts on wildlife and, until recently, the absence of standards for snowmobile emissions and noise. The National Park Service has attempted to address the issue by developing Winter Use Plans that establish regulations and limits at individual park units. These plans have been the subject of numerous legal challenges. On September 15, 2008, the U.S. District Court for the District of Columbia vacated the National Park Service's most recent Winter Use Plan for Yellowstone National Park. The plan would have allowed up to 540 snowmobiles per day into the park beginning in the 2008-2009 winter season, provided that they met noise and emission standards and that the riders were accompanied by commercial guides. The NPS plan was opposed by environmental groups and the vast majority of public commenters. With the rule vacated, it is unclear what limits will apply in the coming winter season.
Current model snowmobiles emit significant quantities of pollution. In one hour, a new model snowmobile emits as much hydrocarbon as a 2008 model auto emits in about four years (54,000 miles) of driving. The Environmental Protection Agency (EPA) promulgated regulations limiting air emissions from snowmobiles in 2002, but the regulations have the effect of allowing the machines to emit as much hydrocarbon pollution in a day as a new auto emits in its lifetime. Snowmobiles also emit significant amounts of noise. EPA has no snowmobile noise standards.
The National Park Service has allowed snowmobile use in 43 units of the national park system, in many cases in apparent violation of Executive Orders from the Nixon and Carter years. Outside of Alaska (where snowmobiles are permitted in most national parks by law), the most popular national park for snowmobiling has been Yellowstone, which saw more than 87,000 snowmobile visits in the 2001-2002 winter season. Under the Clinton Administration, the Park Service decided that the emissions and noise from snowmobiling were incompatible with protecting the park, and promulgated rules that would have phased out snowmobiles from Yellowstone by the winter of 2003-2004. The Bush Administration revisited these rules and announced modifications in March 2003 that would have allowed continued use of snowmobiles. The 2003 rules and the Clinton Administration action have been the subject of conflicting court rulings: a federal court in Wyoming has vacated and remanded the Clinton Administration's phaseout, while a D.C. federal court has vacated and remanded the Bush Administration rules. For the last four winters, Yellowstone and two neighboring park units have operated under a temporary plan that permits 720 snowmobiles per day in Yellowstone, but sets standards for their emissions and requires snowmobilers to be accompanied by commercial guides. Under these rules, snowmobile visits have declined by two-thirds.
Efforts to reduce snowmobile emissions and noise remain contentious. This report discusses snowmobile access to the parks, snowmobile emissions, EPA's emission standards, and congressional efforts to address these issues.