Sounds associated with oversnow vehicles, such as snowmobiles and snowcoaches, are an important management concern at Yellowstone and Grand Teton National Parks. The John A. Volpe National Transportation Systems Center's Environmental Measurement and Modeling Division is supporting the National Park Service with its on-going Winter Use Planning program. As part of this support, acoustic measurements of ten snowcoaches and six snowmobiles were made at the south entrance to Yellowstone National Park from the 26th through the 28th of February 2008. Measurement methodologies were guided by SAE J1161 and SAE J192. There were two primary objectives: 1) to determine which snowcoaches had the Best Available Technology (BAT) with respect to noise emissions, and 2) to determine if there was a significant difference between snowmobile sound levels when tested using two revisions of SAE J192.