Frequently Asked Questions

  1. What are the main chemicals of concern in snowmobile emissions?

    Air quality concerns have generally focused on carbon monoxide (CO), hydrocarbons (HC), and particulate matter (PM), as well as a variety of gases classified as "toxic air pollutants," including benzene, 1,3-Butadiene, formaldehyde, and acetaldehyde.

  2. How do four-stroke emissions compare with two-stroke emissions?

    In general, four-stroke engines emit less unburned hydrocarbons (HC) and particulate matter (PM), about the same amount of carbon monoxide (CO), and more oxides of nitrogen (NOx) than two-stroke engines. For a comparison of commercially available 2002 emissions, please see Laboratory Testing of Snowmobile Emissions.

  3. How does four-stroke engine performance compare with two-stroke engine performance?

    The basic strength of the two-stroke engine is that every second stroke is a power stroke. Only one in four strokes is a power stroke in a four-stroke engine. This fundamental difference provides a significant power-to-weight advantage for the two-stroke engine. While the two-stroke engine has an advantageous power to weight ratio, it is noisy and releases high levels of hydrocarbons directly into the atmosphere.

  4. What are the possible technological solutions to reducing harmful emissions from snowmobile engines?

    Technological solutions that could reduce harmful emissions from snowmobile engines include:

    • Substituting four-stroke engines for two-stroke engines to improve fuel economy and reduce emissions.
    • Introducing fuel injection to replace carburetors in new two-stroke machines.
    • Improving fuel atomization in two-stroke engines for leaner burning mixtures.
    • Treating exhaust to reduce emissions from two-stroke engines.
    • Substituting rotary four-stroke engines for two-stroke engines to maintain power-to-weight ratios of the two-stroke engine.
    • Using ethanol blend gasoline and biodegradable lubricants.
    • Developing electric snowmobiles

  5. Can fuel, lubricant, and engine changes solve these problems?

    The use of bio-based fuels and bio-synthetic lubricants, proper engine set-up (such as tuning the snowmobile engine for the elevation being visited), and other two-stroke engine technologies have produced moderate reductions in emissions.

  6. How effective are ethanol blend fuel and low emission lube oils at reducing emissions?

    Of the fuel blends that had been tested as of 2000, ten percent ethanol blend showed the greatest promise for reducing emissions. The best choice of lubricant was less cut-and-dried, but lubricants were shown to have a real impact. Ethanol blend and low emission lube oils in two-stroke engines have been shown to reduce emissions of carbon monoxide by 7 to 11 percent, particulate matter by 25 to 70 percent, and hydrocarbons by 16 to 38 percent. Use of 10 percent ethanol blend requires no engine modifications or adjustments.

  7. Why is snowmobiling in the National Parks controversial?

    Concerns and criticisms have included 1) various possible impacts on wildlife; 2) degradation of air quality; 3) health effects of emissions on snowmobile riders, rangers, kiosk operators, and mechanics; 4) impacts on aesthetic and wilderness values; 5) noise; and 6) water pollution. Supporters of snowmobiling in the National Parks dispute these criticisms and also point to considerations including 1) the availability of technologies to make cleaner, quieter snowmobiles; 2) economic benefits to local communities; 3) the importance of preserving access to public lands; and 4) traditional patterns of use.

  8. How many snowmobiles visit Yellowstone each year?

    In 1998-99 76,000 tourists visited Yellowstone on about 63,000 snowmobiles. Between 1992 and 1999, an average of 66,619 snowmobiles entered the park each year.

  9. Where are the popular entrances to the park?

    Snowmobiles may ride into the park from the East, South, and West Entrances. Over 60% of snowmobiles have generally used the West Entrance.

  10. Are snowmobiles allowed in every area of the park?

    As of the year 2001, snowmobiles were allowed only on designated unplowed roads in the park, and only during times specified by the National Park Service. The winter season runs approximately three months, from mid-December to mid-March, although dates may vary.

  11. What is the effect of snowmobiles on aesthetic and wilderness values?

    The sound level of snowmobiles is an issue with regard to aesthetics and wilderness values. For example, on some days it is difficult for most visitors to travel to an area in Yellowstone National Park where the sound of snowmobiles is not present. Other people, however, state that the sound of snowmobiles has no impact on their ability to enjoy National Parks or wilderness areas.

  12. How long have snowmobiles been used in Yellowstone?

    The first snowmobiles entered Yellowstone Park in 1963.

  13. What is the economic impact of snowmobiling for communities near Yellowstone?

    Many local economies rely in part on revenues from park visitors in the winter. Some have voiced concern that eliminating over-snow travel and snowmobiles in particular or closing an entrance to the park during the winter could have a detrimental effect on local economies. The magnitude of these economic impacts is hotly debated. For example a 1993-5 study concluded that expenditures by nonresident snowmobilers spent $109 million annually in Wyoming. The University of Montana Bureau of Business and Economic Research estimated that non-resident snowmobilers spent over $44 million dollars in Montana during the 1997-98 season. On the other hand, a 2000 economic study funded by the National Park Service concluded that economic impacts to the town of West Yellowstone from a phaseout of snowmobiling would be in the range of $5 million per year, believed by some to have inconsequential effects on the economy as a whole.

  14. What is the phase-out plan for Yellowstone?

    The NPS Winter Use Plan signed in January 2001 calls for snowmobiles to be phased out of Yellowstone, Grand Teton National Park, and the John D. Rockefeller, Jr. Memorial Parkway. Under the plan, snowmobilers will be allowed to continue using the parks during the winter of 2001-2 with some new restrictions. Use would continue during 2002-3, but at a 50 percent reduced level. In 2003-4 the phaseout of recreational snowmobiles would be complete. See the Regulations section for more detail.

  15. Is snowmobiling allowed in other national parks besides Yellowstone?

    In 2001, snowmobiling is permitted 40 units of the National Park Service, according to the Code of Federal Register. Of these, only seventeen, including Yellowstone, are National Parks.

  16. What is the Organic Act?

    In 1916 the United States Congress passed the Organic Act, whose language defines the National Park Service and its basic mandate. The Act forbids degrading the National Parks and requires the National Park Service to "conserve the scenery and the natural and historic objects and the wildlife therein and to provide for the enjoyment of same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations."

  17. Has the EPA established emissions standards for snowmobiles?

    Under the Clean Air Act, the EPA has the authority to establish emissions standards for snowmobiles.  As of 2001 the agency is at least two or three years away from setting any such standards, which then would not take effect for additional years.

  18. Are there proven health risks for snowmobile riders?

    Exposure to air pollutants is associated with numerous effects on human health, including increased respiratory symptoms or decreased lung function, hospitalization for heart or lung diseases, or premature death. Recent studies conducted by the National Park Service, Air Quality Division, and other scientists have highlighted the potential effects on human health from exposure to air pollutants, specifically snowmobile emissions. See the Air Quality and Personal Exposure sections for more detail.

  19. What are the documented health risks for mechanics, toll booth workers, and patrol rangers?

    A 2000 study showed that mechanics, toll booth workers, and patrol rangers were exposed to levels of benzene exceeding both the acute and intermediate Minimal Risk Level established by the Agency for Toxic Substances and Disease Registry. Exposure levels for toluene and fine particulate matter were also high enough to cause potential long-term health risks.

  20. What is the effect of snowmobiles on water quality?

    As of 2001, the effect of snowmobiles on water quality has not been as well-studied as air quality impacts, but snowpack samples near heavily traveled snowmobile trails have been correlated with elevated levels of ammonium, sulfate, benzene, and other carbon compounds from gasoline combustion, raising concerns about water quality.

  21. What are the documented concerns about snowmobile noise?

    Studies in 1999-2000 showed that kiosk workers and patrol rangers in Yellowstone were subjected to noise levels exceeding OSHA standards. Excessive noise levels can result in permanent hearing loss and can also raise blood pressure. Studies have shown hearing loss for persons subjected to 73 decibels of noise for 8 hours per day for 40 years, or when subjected to 85 decibels over a shorter number of years. Kiosk workers have been exposed to average noise levels of 88 decibels over an 8-hour work day, and a February 2000 study showed patrol rangers exposed to 93 decibel levels.

  22. How many snowmobilers are there?

    According to the American Council of Snowmobile Manufacturers, there are more than four million snowmobilers in the United States and Canada.  Information about snowmobile registration and sales is available from the International Snowmobile Manufacturers' Association.

  23. What is the Clean Snowmobile Challenge?

    The Clean Snowmobile Challenge is an annual design competition for college students first held in 2000. The goal of the competition is to develop a snowmobile with improved emissions and noise characteristics that does not sacrifice performance. A primary sponsor of the competition is the Society of Automotive Engineers.