Officials are touting Yellowstone National Park’s latest winter-use plan as a long-term solution, and conservation groups have met the proposal with tempered approval.

The environmental plan, mostly unchanged from a draft version released last summer, regulates snowmobiles and snow coaches based on limiting their collective noise, air pollution and wildlife impacts, rather than daily numbers.

It allows up to 110 “transportation events” through park gates each day, defined as a single snow coach or a group that averages seven snowmobiles.

The Greater Yellowstone Coalition — which has repeatedly litigated against Yellowstone winter-use regulations in the past — had a mostly positive reaction after reviewing the plan, released Friday. 

“We’re hopeful that this is on the right track,” said Mark Pearson, the coalition’s conservation program director, “and that we’re going to be able to thread the needle here and further improve the conditions in the park.

“We’ve always wanted them, first and foremost, to protect wildlife and the soundscape and the air quality in the park,” Pearson said. “This plan’s best-intentioned. It certainly is vastly cleaner and quietly than it was in 2000.”

The environmental plan does increase the maximum number of snowmobiles permitted and, for now, decrease the number of snow coaches permitted.

Under an interim plan in effect for the past four winters, up to 318 snowmobiles and 78 snow coaches were permitted per day. At maximum levels, the new plan allows 480 snowmobiles and 60 snow coaches. If snow coaches reach a new “best available technology” standard, the allotment could be doubled to 120.

Dan Wenk, Yellowstone’s superintendent, said a breakthrough of the new plan was transitioning from a focus on numbers to impacts on park resources.

“We’ve been working very hard with all the stakeholders,” Wenk said, describing them as the business, environmental and access communities.

“We had some potential flaws pointed out to us,” the superintendent said. “We were able to see those and adjust.”

Improvements from previous iterations of Yellowstone winter-use plans include lower air pollution limits, Wenk said.

“We’ve included incentives for making snow coaches even quieter,” Wenk said. “We have much more robust standards for snowmobiles as well. They include making individual snowmobiles 25 percent cleaner and 50 percent quieter initially.”

Pro-snowmobile groups seemed equally pleased with the final version of Yellowstone’s winter-use plan.

“I think at first blush it is a balanced plan,” said Jack Welch, a special projects consultant with the Blue Ribbon Coalition. “I think for my organization it would be important to resolve this and come up with a long-range plan that doesn’t get challenged in the courts.”

Stability with winter regulations in the world’s first national park is something that’s lacked, Welch said.

Litigation has stalled implementation of new winter-use plans time and time again. The final environmental document released Friday is the seventh proposal since 2001.

“It’s been on-again, off-again for the last 12 years,” Welch said. “I know it’s been tough, especially for the communities — West Yellowstone is a snowmobile community.”

After a rule is issued, expected in the next couple weeks, there will an “adaptive management framework” developed as a supplement to the plan, Wenk said. That framework will allow for changes to the plan over time, he said.

“I think when we do a plan like this, our hope is it could last up to 20 years,” Wenk said. “We have a robust adaptive management component that we’re going to invite all the stakeholders to help us develop.”

— The Associated Press contributed to this story.