A preferred plan for managing winter visits to Yellowstone National Park would further cut the number of snowmobiles allowed to enter the park each season.

Released Thursday for public comment, the National Park Service’s preferred alternative for winter use would differ from past plans most significantly in that it provides different limits for snowmobiles and snowcoaches day to day.

In total, there would be four different levels of use, with the daily schedule set and released to the public a full year in advance.

On average, a total of 254 snowmobiles and 63 coaches would be allowed into Yellowstone each winter day under the draft plan. That compares to the daily limit of 318 snowmobiles and 78 snowcoaches that has been in effect for the past two seasons. That 318/78 level would remain in effect for the 2011-’12 season, with a new plan taking effect in December 2012.

In terms of actual use, Yellowstone has averaged 220 snowmobiles and 34 snowcoaches per day over the past four seasons.

“Much of the variation and use per day (in the preferred new plan) is reflective in some way of the current levels of use and operation,” said Yellowstone Superintendent Dan Wenk in a Thursday conference call with reporters.

The Park Service writes in its draft Environmental Impact Statement, “Although there may be fewer winter use opportunities under alternative seven (the preferred alternative), it is expected that this level would meet user demand and better preserve the resources that make up the visitor experience.”

The preferred alternative passes over other options the Park Service considered, including banning all snowmobiles, going back to allowing 720 sleds a day and plowing more Yellowstone roads for wheeled vehicles.

In the conference call, park officials said the proposal to reduce snowmobiling levels was not as much to protect Yellowstone’s ecosystem, as to offer a quieter experience for Yellowstone visitors.

David Jacob, a Park Service employee who led the project, said the environmental impacts of having 330 snowmobiles and 80 snowcoaches a day are minimal.

“So it’s not a biological reason for having less, it’s user experience,” Jacobs said.

“I would tell you that the science didn’t give us a number,” said Wenk, saying he thinks the numeric limits can be debated. He said the 330/80 figure was based on “a total look at both the experience and the patterns and the expectations that we all have collectively.”

Wenk said the reduced-use days are the Park Service’s attempt to respond to the expectations and desires of the park’s winter visitors.

“I think it’s a result of the public scoping (comments) we heard,” said Wenk of the new emphasis on non-motorized use like skiing and snowshoeing.

The draft document says the varying limits on snowmobile use would allow park visitors to choose what kind of experience they want in Yellowstone.

“If OSV (oversnow vehicle) noise would detract from a visitor’s experience, that visitor can plan a visit for a time with lower OSV use; if OSV use is a critical part of a visitor’s experience, they can plan for a day with higher OSV use,” the impact statement says.

Under the preferred alternative, Wenk said that in some years the traditionally highest-use holidays (Christmas, New Year’s, Martin Luther King Jr. Day and President’s Day) might allow the maximum of 330 sleds and 80 coaches. Other years, a holiday could have a lower limit to provide more quiet and solitude for skiers and snowshoers.

The alternative preferred by the Park Service also differs from past plans in that it would allow commercial guides to swap their daily permits with other operators at other gates to meet demand. So if a big group of more than the maximum of 22 snowmobiles wanted to come through the East Entrance one day, the outfitter could arrange that by exchanging permits with an operator at, say, the West Entrance.

Swapping permits to better meet actual demand could help keep permits from going unused as they often are currently.

All coaches and sleds would continue to have to be led by a commercial guide. Cleaner, four-stroke snowmobiles would continue to be required for touring in the park, and, for the first time, clean technology standards would be set for snowcoaches, too.

The Park Service said it would consider placing additional clean technology requirements on snowmobiles as technology improves. Operators using cleaner vehicles could receive more permits, the document says.

The new plan would cost the Park Service roughly $3,953,550 each winter, just slightly less than the cost of how officials have managed Yellowstone the last few years. That’s due to some routes on the eastern side of the park closing to snowmobiles and coach use when the East Entrance closes instead of staying open another week and a half.

Of the $3.95 million cost, $2.15 million would be for staff, $789,000 for spring opening, $325,000 for managing Sylvan Pass, and $314,640 for road grooming.

Under a previous preferred alternative released in 2008, the Park Service had proposed closing the East Entrance in the winter, citing the expense and safety risk of managing avalanches on Sylvan Pass. But after local officials and citizens objected, the Park Service reached an agreement to keep the pass open, but with a season that starts a week later and ends a week earlier than the rest of Yellowstone. The preferred alternative continues that agreement.

The new document released Thursday cites some risk associated with managing avalanches on Sylvan Pass, but says that current practices “would ensure that the pass would continue to operate in a manner that would minimize risk to (Park Service) staff.”

The road from Gardiner to Cooke City will continue to be plowed as it has.

This plan is the Park’s Service fourth attempt at crafting a permanent plan for winter use in Yellowstone. Three previous plans have been voided by federal judges over the past decade after legal challenges by environmental groups — who want all snowmobiles out of the park — and snowmobile advocates — who would like to see past, higher limits reinstated.

“I anticipate that we will have support and opposition for various parts of this preferred alternative,” said Wenk, saying he expects a “very vibrant discussion.”

He said he’s looking to engaging with folks about the plan, which will include a meeting in Cody on the evening of June 2.

“I’m very interested to hear what the public has to say,” Wenk said, adding that the Park Service expects to modify its proposal somewhat based on whatever it hears.

The nearly 550 pages of the document and its attachments are available online at http://parkplanning.nps.gov/yell, where comments may also be submitted.

You can request a copy of the document on CD or in hard copy and submit written comments to: National Park Service, Management Assistant’s Office, P.O. Box 168, Yellowstone National Park, WY 82190.

The 60-day comment period is expected to close July 13.