Editor's note: Updates with comments made during conference call with Yellowstone officials, and reaction from National Parks Conservation Association and Coalition of National Park Service Retirees.

A preferred approach by Yellowstone National Park officials to managing winter use in the park wouldn't significantly alter the number of snowmobiles or snowcoaches allowed to enter the park compared to recent years.

The proposal, one of seven alternatives released Thursday in the park's Winter Use Plan Draft Environmental Impact Statement, will be open for public comment for 60 days. Park officials hope to have a final plan approved before next winter, although it wouldn't take affect until the winter of 2012-13.

Under their preferred alternative, as many as 330 snowmobiles and 80 snowcoaches, or as few as 110 snowmobiles and 30 snowcoaches, would be allowed into the park per day during the 90-day-long winter season. Over the length of the winter season, the proposal would allow a daily average of 254 snowmobiles and 63 snowcoaches into the park, numbers somewhat higher than traffic seen during the past two winters yet below the current upper limit of 318 snowmobiles and 78 snowcoaches per day.

"The average number of snowmobiles per day has been 194, and the average number of snowcoaches per day has been 40," Yellowstone Superintendent Dan Wenk said during a roughly 40-minute conference call with reporters. "If you look at the numbers that would be included within our preferred alternative, I believe the average number of snowmobiles could be 253, excuse me, 254, and 63 snowcoaches. ...Much of the variation in the use per day is reflective in some ways of the current levels of operation.”

At the National Parks Conservation Association, officials said the park's preferred alternative is really no change in managing over-snow travel in the park than what has been done the past two years under an interim plan ordered by Interior Secretary Ken Salazar while park staff worked on the latest environmental impact statement on winter use.

"The preferred alternative is essentially the status quo," said Patricia Dowd, program manager for NPCA's Yellowstone Field Office. "The question that remains is, 'Does the preferred alternative best protect Yellowstone?' We think the answer to that is ‘no.’”

At the Coalition of National Park Service Retirees, Rick Smith, who chairs the group's executive council, said he hadn't had time yet to analyze the entire document.

"But at first glance, it seems that the park has recognized that in the public scoping process, less than 1 percent of the comments received favored more snowmobile use. By preserving the status quo in terms of number of snowmobiles, the park is recognizing what the market trends are already telling them: people prefer to make their winter visits to the park via snowcoaches," said Mr. Smith.

"We should honor the park and its scientists for recognizing that the impacts of only four or five years ago were unacceptable.  The question now is, is the preferred alternative the best we can do to protect America’s first national park?" he continued.

Under the DEIS's preferred alternative, the daily number of snowmobiles and snowcoaches allowed into the park would be based in part on past winters' traffic patterns and in part on what the public wants, Superintendent Wenk said during the conference call.

For instance, during half the winter season -- 45 days -- up to 330 snowmobiles and 80 snowcoaches would be allowed in the park. The bulk of the snowmobile numbers -- 176 -- would be permitted through the West Yellowstone Entrance, while 110 would be allowed through the South Entrance, 22 through the East Entrance, 11 through the North Entrance, and 11 originating from Old Faithful.

Thirty-six snowcoaches would be allowed through the West Yellowstone Entrance under this scenario, with 14 permitted through the South Entrance, two through the East Entrance, a dozen through the North Entrance, and 16 originating from Old Faithful.

For 30 days of the 90-day winter season, up to 220 snowmobiles per day would be allowed into the park, with half allowed through the West Yellowstone Entrance, 66 through the South Entrance, 0-22 through the East Entrance, 11 through the North Entrance, and 11 from Old Faithful. Under this scenario, up to 50 snowcoaches a day would be allowed in the park, with 22 permitted through the West Yellowstone Entrance, eight through the South Entrance, 0-2 through the EastEntrance, eight through the North Entrance, and 10 originating from Old Faithful.

For 16 days of the winter season, between 110 and 143 snowmobiles per day would be allowed in the park, with 66 allowed through the West Yellowstone Entrance, 44 through the South Entrance, 0-11 through the East Entrance, 0-11 through the North Entrance, and 0-11 from Old Faithful. Under this scenario, between 30 and 80 snowcoaches would be allowed in the park on a daily basis, with 12 permitted through the West Yellowstone Entrance, six through the South Entrance, none through the East Entrance, six through the North Entrance, and six from Old Faithful.

The various scenarios that show zero entrances allowed via the East and North entrances reflect seasonal closures affecting over-the-snow traffic in those areas of the park.

How officials settled on the 330-snowmobile-per-day upper limit was not clearly explained, other than that "it was fairly clear that the level around the interim level, 318, was more protective of resources than the higher levels (approaching 720 per day), said David Jacob, who managed the DEIS project from his Denver Park Service office.

Neither Superintendent Wenk nor Mr. Jacob were familiar with an Environmental Protection Agency determination, made back in 2007, that allowing more than 250 snowmobiles per day into Yellowstone could be detrimental to both park visitors and wildlife. It is possible that technological advances in snowmobiles since that study was made make its conclusions obsolete, although Ms. Dowd didn't seem to think circumstances had changed.

"What’s going to happen when there’s 330 snowmobiles in the park? That exceeds all the science that indicates impacts occur when there’s more than 200-250 snowmobiles in the park," she said.

Mr. Jacob, though he wasn't familiar with the EPA findings, didn't think 330 snowmobiles and 80 snowcoaches a day would significantly impact wildlife.

“The impacts are minimal and so it’s not really a biological reason for having less,” he said.

As in recent years, the preferred alternative would continue to require that snowmobiles and snowcoaches be accompanied by commercial guides and on existing park roads groomed for oversnow use. Sylvan Pass and the East Entrance to the park would be managed with a combination of avalanche mitigation techniques to provide winter access in accordance with an agreement reached in 2008. A new over-snow vehicle scheduling plan would require that all vehicles entering the park do so by 10:30 a.m. each day.

Among the seven alternatives contained in the draft EIS, in addition to the park's preferred option one called for not allowing any motorized use, another called for phasing out snowmobiles in favor of snowcoaches, and one proposed allowing up to 720 snowmobiles and 78 snowcoaches per day. The park also considered an alternative that would allow commercial, wheeled vehicles to travel on roads that would be plowed from West Yellowstone and Mammoth Hot Springs to Old Faithful.

Use of "best available technology" (BAT) snowmobiles would continue, and a new limit on nitrogen oxide emissions would be implemented. By the winter of 2014-2015, snowcoaches would be required to meet or exceed the Environmental Protection Agency's (EPA) 2010 emission standards for new wheeled vehicles. Snowcoaches also would be required to meet a new ground-surface weight limit of 4.5 pounds per square inch to limit potential damage to park roads.

Additional details on the Draft EIS, an electronic copy, and a form for submitting public comments on the document electronically via the Internet can be found at this site.

You can request a copy of the Draft EIS in compact disc or printed paper form and submit written, hard copy comments by mail to: National Park Service, Management Assistant’s Office, P.O. Box 168, Yellowstone National Park, WY 82190. Comments may be submitted in writing through the PEPC website, in person, or by mail. Comments will not be accepted over the phone, by fax, or email. No bulk comments will be accepted.

The document is now open for public review and comment. The comment period will close 60 days after the EPA publishes a “Notice of Availability” of the Draft EIS in the Federal Register. That date will be announced soon.  A separate, proposed draft federal rule that would be used to implement the park’s preferred alternative, if chosen, will be released for its own separate 60-day public review and comment period soon.

The park will hold six public meetings: four local meetings in communities near the park and two national meetings. Evening public meetings are scheduled for June 1 in Jackson, WY, June 2 in Cody, WY, June 7 in West Yellowstone, MT, June 8 in Bozeman, MT, June 21 in the Denver, CO, and June 23 in Washington, DC. Further details with specifics on meeting locations will be released shortly.  In addition, two public webinars (online “meetings”) are scheduled for June 21 and June 22.

The National Park Service intends to have a final EIS, a Record of Decision, and a final rule guiding winter use in place before the start of the 2011-2012 winter season.