A preferred winter-use plan for Yellowstone National Park that is crafted around "transportation events" and which could allow more than twice as many snowmobiles into the park on a given day than has been experienced in recent years is open for public comment.

The plan also states that the "maximum daily average number of snowmobiles per day would be 342 by the start of the 2017-18 winter season." That's a number still much higher than current usage levels -- the daily average up through the 2011-12 winter has ranged from 187 to 197 snowmobiles, while daily snowcoach numbers have ranged from 56 to 63 -- but one park officials believe will have minimal impacts on Yellowstone's air, water, wildlife, visitors, and employees.

That preferred proposal was published in the Federal Register today, opening a 60-day public review and comment period.

Highlights of the plan's preferred alternative call for:

* Up to 110 "transportation events" per day; these events are defined as a group of seven snowmobiles or one snowcoach. However, the seven-snowmobiles-per-event would be the seasonal average; there could be times when as many as 10 snowmobiles are packaged in one group. Up to 50 of these events could involve groups of snowmobiles;

* Four non-commercially guided groups of five snowmobiles would be allowed each day of the winter season, one each through the park's Mammoth Hot Springs, West Yellowstone, South, and East entrances;

* Sylvan Pass would remain open for snowmobile and snowcoach access through Yellowstone's East Entrance, with park crews performing avalanche control as needed to ensure safe passage;

* Snowcoaches placed in service for the 2014-15 season, when the plan is scheduled to take effect, would have to feature "best available technology" (BAT) standards for their engine noise and emissions.

By the winter of 2017-18, all snowmobiles and snowcoaches would have to meet the latest BAT standards.

If the plan gains final approval, the winter of 2013/2014 will be a transition year, during which the park will allow motorized over-snow travel under the same conditions in place for the past four winters: up to 318 commercially guided Best Available Technology snowmobiles and up to 78 commercially guided snowcoaches daily.

The proposed rule and an electronic form to submit written comments can be found on this page. It is also available on CD or in hard copy by writing the Winter Use Planning Team, P.O. Box 168, Yellowstone National Park, Wyoming 82190. Written comments may also be submitted in person or by mail. Comments will not be accepted by phone, fax, or e-mail. All public comments must be received or postmarked by midnight, June 17.

Additional information on Yellowstone's winter use planning process including answers to Frequently Asked Questions can be found online.

Yellowstone Superintendent Dan Wenk will use the analysis and recommendations contained in the Final SEIS and comments on the proposed rule to make a final recommendation to the NPS Intermountain regional director regarding the direction of winter use. The regional director, John Wessels, is expected to issue the Record of Decision sometime this summer, after which a final rule to implement the decision will be published in the Federal Register in order to allow the park to open for the 2013/2014 winter season.