This study of over-snow vehicle sound levels was conducted to provide supplemental and additional information for preparation of the Winter Use Plan Supplemental Environmental Impact Statement (SEIS) for Yellowstone and Grand Teton National Parks and the John D. Rockefeller, Jr., Memorial Parkway. The tests conducted in this study resulted from the analysis of previous tests conducted in September 2001. The September tests were done on a grass surface, which is permissible under SAE standards. In order to get the best data possible, these February tests were done on snow under typical winter trail conditions.
The pass-by sound level of a variety of over-snow vehicles was measured at operational speeds that would be experienced under normal use of the vehicles while in the national park units. The pass-by testing included three different types of snow coaches, two commercially available four-stroke snowmobile models, a groomer, and various two-stroke snowmobiles. All testing was conducted on the same day in the same location with the same terrain and background conditions.