Yellowstone National Park’s plan for increasing snowmobile traffic fails to provide clear-cut analysis supporting a key claim that seven snowmobiles have a similar impact as one snow coach, a critic says.

The ratio of seven snowmobile to one snow coach is at the heart of the latest winter-use plan for the world’s first national park. The 400-page supplemental environmental impact statement, released June 29, proposes limits that increase snowmobile traffic by 10 percent and reduce snow coach traffic by 23 percent starting this winter.

Officials aim to manage over-snow vehicles based on “transportation events,” which they define as a single snow coach or group of snowmobiles that averages seven machines. This is “based on the concept of comparability; that impacts to park resources and the visitor experience resulting from a snow coach or a group of snowmobiles are comparable to each other,” the document reads.

Managing winter use with transportation events, park officials say, will simultaneously allow for an increase in visitors while decreasing impacts on wildlife, sound and air pollution.

A critic says the plan never justifies the snowmobiles-to-snow-coach ratio. A consultant for the Bozeman, Mont.-based Greater Yellowstone Coalition highlighted the issue during a public meeting on the plan July 16 at the Virginian Lodge.

“The Park Service is emphasizing that the foundation of its proposal is the idea that the impacts of seven snowmobiles on the park’s resources and visitor experience is the same as a single snow coach,” Jon Catton said. “And yet, they’re publicly acknowledging that the evidence that would allow the public to judge for itself is not in the 400-page analysis.”

At the meeting at the Virginian, he challenged Yellowstone officials on the 7-to-1 comparison.

“I was curious where it shows that and gets into the analysis of the impacts,” he said. “I think that would be very helpful for the public, because, as you said, it’s the premise or the basis for your preferred alternative.

“You’re asking the public to believe that [transportation events] are a good way to go for the future of this park, and yet a 400-page document doesn’t actually say “here’s how that works” with respect to air or sound or wildlife.”

Park officials acknowledged Catton’s point.

“We didn’t sort of wrap it up nicely in a bow as well as perhaps we could have,” Yellowstone winter-use documents manager Dave Jacob said.

His boss agreed.

“I realize that we had not done what he asked,” Yellowstone Superintendent Dan Wenk said in an interview after the meeting. “There’s not a summary table some place that says, ‘This is why seven is equal to one.’ So we need to do it. And I think you’ll see it in the final document.”

The pro-snowmobile BlueRibbon Coalition backs the park’s preferred plan, which is technically called “alternative four.”

“We believe that alternative four is the right way forward for access to the park in the winter,” BlueRibbon’s special projects consultant Jack Welch said. “Certainly clarification is always beneficial, but the comparison is sound,” he said of the 7-to-1 ratio.

Getting to 7-to-1

Litigation started Yellowstone establishing long-term winter-use rules but has stalled implementation time and time again. The draft environmental document up for public review is the seventh major plan for regulating snowmobiles in the park in 12 years.

Under an interim plan in effect from 2009 to this spring, 318 commercially guided snowmobiles and 78 commercially guided snow coaches were admitted into Yellowstone each day during winter.

The new preferred option allows for an average of 350 snowmobiles and 60 snow coaches into the park each day.

Up to 110 “transportation events” would be allowed in the park each day, but no more than 50 daily transportation events could come from snowmobiles. Under the proposal, four of the 50 events can consist of groups that are not commercially guided.

Managing by “transportation events” is cleaner, quieter, and has less impact on Yellowstone resources, park officials say.

“We’re trying to get away from this construct that people have been trained to look at number of vehicles entering the park,” Jacob said at the Jackson meeting.

Wenk agreed.

“We went into this not saying how many machines can we allow, we went into it saying what is the allowable impact,” Wenk said in an interview. “And then we said, ‘If that’s the allowable impact, what does it translate to in terms of snowmobiles and snow coaches?’ That’s how we came up with the numbers.”

The impacts from a single snow coach and seven snowmobiles are “not the same, but they’re comparable,” Wenk said.

The superintendent used sound as an example.

A two-stroke snowmobile with “best available technology” running in the park last year produces about 67 decibels running at 30 mph, the maximum allowable speed. For every doubling in the number of snowmobiles, there are three more decibels of sound energy, Wenk said.

So, two snowmobiles produce 70 decibels, four produce 73 decibels and eight produce 76 decibels, he said.

“A snow coach has to be 75 decibels,” Wenk said. “So, take off one from eight [snowmobiles], and basically, they’re comparable.”

The Yellowstone document said a typical group of snowmobiles is heard for only 17 seconds longer than a single snow coach.

“Data collected at 14 different locations in the park from 2005 to 2011 show that groups of snowmobiles were heard, on average, 3 minutes, 4 seconds, while snow coaches were heard, on average, 2 minutes, 46 seconds,” page 54 of the environmental plan reads.

That means a snowmobile transportation event is 10 percent longer than a snow coach one, according to a News&Guide calculation.

The superintendent also drew a parallel between the impacts of snowmobiles and snow coaches on wildlife.

“Recent behavioral monitoring data and modeling indicates that snowmobiles are slightly more likely to elicit a visible behavioral response from bison or elk, but snow coaches elicit slightly stronger levels of behavioral responses, such as movement or flight,” the document states.

The section of the document addressing air pollution does not explicitly make distinctions between emissions from snow coaches and snowmobiles. It does say that if Yellowstone allowed travel only by snow coaches with the best available pollution technology, a proposal the park does not endorse, there would be substantial reductions in hazardous air pollution emissions compared to the park’s preferred plan.

According to calculations made from tables in the study, a no-snowmobile alternative would reduce formaldehyde emissions by 300 pounds a year, benzene by 260 pounds and acetaldehyde by 100 pounds.

Yellowstone management assistant Wade Vagias acknowledged that when looking at pollution there’s less parity between snowmobiles and snow coaches than when looking at sound or wildlife impacts.

“Probably the biggest discrepancy is how clean a snow coach is and how clean a group of snowmobiles is,” Vagias said. “Snowmobiles are a little bit dirtier than snow coaches.”

Because snow coaches are typically retrofitted buses and vans and are far from uniform, it’s not easy to draw an apples-to-apples comparison in terms of air quality, wildlife and sound impacts, Vagias implied.

In tests conducted earlier this year, some snow coaches “made 65 [decibels], and some made in the mid- to low-80 [decibel range],” Vagias said. The report on those tests is not yet publicly available.

Wenk agreed a comparison is not easy to make.

“It’s a not that neat of a package,” he said, referring to the comparison Catton seeks. “But, in the final document, we need to consolidate that information into one place.”

A historical number

The superintendent added that historical snowmobiles travel patterns also played a role in the proposed daily quota.

“Historically, a group of snowmobiles that has come into the park has been seven,” Wenk said. “In many ways, that was highly influential on how we landed on a group of seven.”

In addition to the park’s preferred plan and the snowcoach-only alternative, Yellowstone examined a business-as-usual plan and one that would bar both snowmobiles and snow coaches.

The National Park Service is shooting to approve its plan before the 2012-13 winter season begins Dec. 15.

While the 2011 draft environmental impact statement drew 59,000 comments and vigorous debate at public meetings, Yellowstone spokesman Al Nash said that response has been a little more tempered this year. Only four people spoke at the Jackson meeting and no comments were submitted, in the West Yellowstone, Mont., meeting, Nash said.

The spokesman did expect a late rush of input in the days before public comment closes Aug. 20.

Not over yet

Besides a more clear-cut explanation for “7-to-1,” Yellowstone officials anticipate other changes to the final plan, Nash said.

“We certainly continue to believe that we presented a good range of alternatives and that our preferred alternative has a lot to offer and a lot of strengths,” he said. “But, I would expect that, based on the public comment that we have and will receive, you will see at the very least some refinement in whatever alternative we select compared to what we presented to the public.”

In particular, Nash said, the park has received a number of substantive comments on the proposal to allow up to 20 snowmobilers a day who are not commercially guided.

The BlueRibbon’s Welch criticized the coalition’s consultant.

“Jon [Catton] has a tendency to form a conclusion — which is that we shouldn’t have snowmobiles in the park — and then come up with reasons why,” he said. “The realities are that seven [snowmobiles] is appropriate, responsible and defensible.”

Catton said he was pleased Yellowstone was planning to comply with his request. He questioned whether Yellowstone has the correct winter-use vehicle ratio.

“The notion of 7-to-1 not being explained in the document, begs the question: ‘Is it really 7-to-1?’” he asked. “And if it’s not, what is it?”

Catton also said Yellowstone’s changes will come in “too late for citizens who right now are evaluating this important choice about Yellowstone’s future.

“It will change after the public has the opportunity to give feedback that might alter the plan,” he said. “It’s unfair and unhelpful to the public.”