Oversnow Vehicle (OSV) Noise Emissions Testing

Photo collage with an oversnow vehicle traveling along the roads in Yellowstone, and a warmly dressed ranger using a monitor.

One goal of Yellowstone National Park's Winter Use Plan and final rule is to create a cleaner and quieter winter-time park experience. As a means of achieving this goal, the final rule specifies new air and noise (acoustic) emissions standards for all oversnow vehicles (OSVs) traveling in the park (see Table 1). All OSVs must operate at or below these Best Available Technology (BAT) standards by the dates listed in the winter use final rule. In addition, if vehicles meet new Enhanced Best Available Technology (E-BAT) emission levels, operators will be able to take advantage of market incentives.

Emission Standards and Timelines
Noise and air emission requirements for snowmobiles continue unchanged until the 2015-2016 winter season, when all snowmobiles are required to meet the new air and noise emission standards (new BAT noise standard of a maximum decibel level of 67 dBA).

Starting in the 2014-2015 winter season, all new snowcoaches brought into service are required to meet the new air and noise emissions standards (new BAT noise standard of a maximum decibel level of 75 dBA). All snowcoaches (new and existing) must meet the new noise and air emission requirements (75 dBA) by the 2016-2017 winter season or be removed from service.

Enhanced BAT
The final rule allows commercial tour operators to voluntarily upgrade their fleets to cleaner vehicles in exchange for an additional OSV per transportation event. As of December 15, 2014, commercial tour operators may voluntarily upgrade their fleets to meet more stringent enhanced air and noise emission standards (described as "Enhanced BAT" or E-BAT). If these voluntary, enhanced standards are met (a maximum decibel level of 65 dBA for snowmobiles or 71 dBA for snowcoaches), the size of a transportation event for that commercial tour operator may increase from a seasonal average of 7 to 8 snowmobiles per event and from 1 to 2 snowcoaches per event, not to exceed a seasonal average of 1.5 snowcoaches per event.

Table 1. New BAT and E-BAT Noise Standards for Yellowstone National Park OSVs

Snowmobiles 67 dBA @ 35 MPH 65 dBA @ 35 MPH
Snowcoaches 75 dBA @ 25 MPH* 71 dBA @ 25 MPH*
*Or the average cruising speed of the vehicle if less than 25 MPH

Through its Adaptive Management Program, the NPS is developing a snowcoach BAT approval and certification process. As part of this process, the NPS will test and certify snowcoaches in the field for compliance with the new BAT air and noise emissions standards. The NPS closely follows the standard procedure outlined by the Society for Aircraft Engineers, known as SAE J1161 – the Operational Sound Level Measurement Procedure for Snow Vehicles (updated November 2013) - to measure each OSV's noise emissions at cruising speed. Vehicle sound levels are recorded in decibels (dBA).

The NPS has and will continue to test snowmobile noise emissions to support NPS-led computer modeling, comparability assessments, validation of manufacturer reported noise emission levels, and to provide data to commercial operators about the performance of their current snowmobile fleet. However, the NPS will not certify snowmobiles as BAT-compliant for noise or air emissions. The NPS will continue to rely on snowmobile manufacturers to certify snowmobiles.

Available Datasets

Contact the Park

Mailing Address:

P.O. Box 168
Yellowstone National Park, WY 82190-0168


(307) 344-7381
Recorded information. For road and weather information, please dial 307-344-2117.

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