"Political pressure" has forced the National Park Service to soften its approach to minimizing the impacts of over-snow traffic in Yellowstone National Park, a coalition of groups charges in comments submitted on the park's latest winter-use plan.

The allegations of undue influence by the Office of Management Budget were made by the Coalition of National Park Service Retirees, the National Parks Conservation Association, the Greater Yellowstone Coalition, the Natural Resources Defense Council and the Winter Wildlands Alliance.

"... we are concerned that this rulemaking is moving down a path that has plagued Yellowstone, the National Park Service, a broad spectrum of stakeholders, the park’s visitors, and the nation’s taxpayers for far too long," the coalition wrote in comments submitted last week. "Through additional years of costly NEPA (National Environmental Policy Act) analysis, NPS has identified steps needed to protect Yellowstone in accordance with its conservation mandate.

"Now, at the rulemaking stage, it appears the agency has come under political pressure at odds with NPS’s professional judgment and in contravention of the agency’s legal obligation to assure conservation of the country’s flagship national park."

Yellowstone officials also did not immediately respond to whether they had been politically pressured to soften their winter-use plan.

As Yellowstone staff works on finalizing the winter-use management plan, the groups have asked that they strengthen that plan with an eye on improving the park's soundscape and air quality.

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.

The park's proposed alternative, the groups maintain, is weak in the time it allows to pass before fully implementing "best available technology" standards for over-snow vehicles, by not requiring non-commercially guided snowmobiles to meet those BAT standards, and by failing to explain how the park plans to keep noise from being a "major adverse impact" on Yellowstone.

"NPS’s plan contains thoughtful strategies to reduce adverse impacts to the park. However, it also maintains deficiencies identified in the judicial opinions that overturned Yellowstone’s 2003 and 2007 plans," the groups wrote. "The public and the park need the Obama Administration not to repeat these errors."

To that point, the groups ask that park planners:

• Fully implement the BAT standards specified in the SEIS by the 2015-2016 winter season rather than waiting for the 2017-2018 season;

• Require non-commercially guided snowmobiles to meet the new-BAT standard like all other snowmobiles.

• Specifically address in the Record of Decision and Final Rule monitoring results that reflect recent use has exceeded the park’s soundscape thresholds for a “major adverse effect” and explain how NPS expects this to change under the Final Rule.

• If NPS expects that adverse impacts of its winter use plan will exceed those of recent winters, this should be stated in the ROD and Final Rule as part of NPS’s rationale for its choice.

• Explicitly state in the ROD and Final Rule that the Desired Future Condition for Yellowstone is a cleaner and quieter park than visitors and wildlife have actually experienced in recent winters.

In their nine pages of comments, the groups say that while progress has been made in improving winter conditions in Yellowstone, problems still remain along the key travel routes taken by snowmobiles and snowcoaches.

"In the park’s travel corridors, where winter visitors spend most of their limited time, noise disproportionately caused by snowmobiles has continued to exceed Yellowstone’s threshold for a 'major adverse effect,' creating what the park terms 'an easily recognizable adverse effect on the natural soundscape and potential for its enjoyment,'” they wrote.

"...Moreover, in the current supplemental analysis, NPS determined through direct testing of vehicles on Yellowstone’s roads that “BAT” snowmobile models certified for use in the park have not become progressively cleaner and quieter, as manufacturers had pledged, but rather have grown noisier and more polluting," they added. "Despite this, NPS has again proposed an increase in snowmobile use to a level much higher than the actual level seen in recent winters."