Understanding Oversnow Vehicle Noise Impacts

The 2006 National Park Service Management Policies (NPS 2006) state that natural soundscapes are to be preserved or restored as is practicable because the unimpaired sounds of nature (natural soundscapes) are a valued resource at national parks. Historical numbers of oversnow vehicle usage in Yellowstone and Grand Teton National Parks and the John D. Rockefeller, Jr. Memorial Parkway created unacceptable adverse impacts on natural soundscapes (NPS 2000; NPS 2003). The 2004 temporary winter use plans environmental assessment reaffirmed these conclusions and established acoustical indicators and standards to mitigate the impact of noise from oversnow vehicles on the natural soundscape (NPS 2004). The winter soundscape at Yellowstone and Grand Teton National Parks consists of natural and non-natural sounds, although extreme quiet also can be experienced in both parks. Natural soundscapes are often important for wildlife survival due to the use of acoustic communication during breeding and predator/prey interactions. Common natural sounds include bird calls, mammal vocalizations, flowing water, wind, and thermal activity. Non-natural sounds include wheeled vehicles, aircraft, and the sounds associated with other human activity and facility utilities in visitor and employee developed areas. The subject of this paper, however, is the sound of oversnow vehicles (snowmobiles, snowcoaches, and snowgroomers). Extensive information on the impacts of oversnow vehicles on the natural soundscapes of Yellowstone and Grand Teton National Parks has been gathered through intensive acoustical monitoring, modeling, and targeted research the past four years. Direct measurements of oversnow vehicle pass-bys, continuous acoustic monitoring throughout the winter, and sophisticated computer modeling all estimate the sound levels and percent of time that snowmobiles and snowcoaches are audible. A few details of these different approaches follow