There are times during the hardest of Rocky Mountain winters, when the mercury slides far below zero, that Yellowstone Lake’s heavy mantle of ice grinds and groans under the pressure of shifting flows. Snow can fall so deeply on Yellowstone National Park in Wyoming’s northwestern corner that workers at times must clamber onto the rooftops of lodges and cabins to shuck off the drifts so they don't collapse the roofs.

And after the storms are spent, when the sun slowly scales cerulean skies and flares the crystal-coated lodgepole and Ponderosa pines and the steam-wrapped faces of bison, you stand in awe at the landscape. And you listen to it, as well. To the guttural throttling of Old Faithful, Castle, and Riverside geysers in the Upper Geyser Basin. To the splashing and bubbling of hot waters from the springs. To the raspy calls of stellar jays and howls of wolves.

These are the things that lure thousands of visitors to the world’s oldest national park during its harshest of seasons. While there are those who ski or snowshoe into the park, far and away most arrive on the backs of snowmobiles or within the coaches of track-clad vans and buses. Though seemingly insignificant in this incredible setting, these conveyances are responsible for one of, if not the, most contentious issues ever to confront the National Park Service.

While the debate surrounding over-snow vehicles in the park dates back decades, in just the past ten years the Park Service has spent a reported $11 million on resource-impact studies and monitoring. At least 850,000 people -- closer to 900,000 when you consider the latest temporary winter-use rule -- have commented on snowmobiles in the park, with about 80 percent of those folks supporting a phase-out of snowmobiles, according to park officials.

This winter’s plan, which goes into play effect Tuesday when the park opens its gates to over-snow travel (although a paucity of snow might force companies to put the wheels back on their coaches and park the snowmobiles), was delivered by fiat from Interior Secretary Ken Salazar. Back in July he ordered daily limits of 318 snowmobiles and 78 snowcoaches this winter and next and told Yellowstone officials to take another shot at developing a sound and defensible winter-use plan. And so park officials are embarking on their fourth environmental impact statement on the issue.

Perhaps one problem to achieving an acceptable solution is that the National Park Service seems mired in an effort to justify one form of transportation over another, or both side by side, rather than asking the more basic question of should there be over-snow travel in Yellowstone in winter?

Regardless, it has been said that if you wait long enough, a study will arrive to bolster your point of view. In a new book, Repairing Paradise, the Restoration of Nature in America’s National Parks, author William Lowry points out that “(T)he impact of scientific evidence on policy change proposals is not always clear, and the role of science in recent political debates on many issues has been controversial. Different sides often present their own versions and interpretations of scientific evidence.”

And that seems to be the case in the long, meandering, and politically charged path Yellowstone managers have followed in trying to develop a winter-use plan. While each of the first three EISes pointed out that snowcoaches were the environmentally preferred alternative for over-snow travel in the park, technological advances have led to cleaner-running 4-stroke snowmobiles and narrowed, if not eliminated, the past disparities, according to Yellowstone officials. Not long after Secretary Salazar established the over-snow limits, park officials were disseminating snippets of reports that they said showed that snowmobiles have no greater impact on the resources than do snowcoaches.

* “Best available technology” engines have reduced snowmobile emissions so much that they are “are now very similar in their per passenger emissions” with snowcoaches, park officials noted.

* Snowcoaches fluster wildlife slightly more so than snowmobiles, due to the rig’s larger profile, they said.

* Noise studies show the two over-snow vehicles are comparable when it comes to noise, they pointed out.

Indeed, as they continue to assess winter travel, at times it appears that Yellowstone officials have developed a bias, or push back, against snowcoaches after all the previous studies that implicated snowmobiles as the foremost source impacting the park’s resources.

* In briefing the Obama administration’s Interior Department staff on the winter-use issue in March 2009, Yellowstone officials portrayed snowcoaches as fuelish (“coaches typically get 3-4 miles per gallon; snowmobiles get 20 mpg”) and uncomfortable (“many current coaches are not optimal for winter viewing....cramped, with windows that fog or ice up in cold weather”) while describing snowmobiles as having improved dramatically, technology-wise, with the advent of 4-stroke snowmobiles.

* In that briefing paper, park officials said the commercial guiding requirement provides “excellent service to visitors, outstanding safety, and accountability...” And yet, in February 2006, with the guiding requirement in place, a woman was killed when she crashed her snowmobile off the road between Norris and Canyon.

Those who favor snowcoach-only travel question the park's data, noting that the emissions study compared “best available technology” snowmobiles against a mix of old and new technology snowcoaches rather than only the best snowcoach technology, which, just as 4-stroke snowmobiles are cleaner than their older 2-stroke relatives, makes the newer coaches decidedly cleaner than the older ones; that there are more snowmobiles in the park than snowcoaches, and so more opportunities to startle wildlife; that soundscape studies certainly seem to indicate that noise goes down when snowmobile numbers go down.

John Sacklin, a management assistant in the park who has worked on the winter-use issue for at least the past decade, denies there’s a bias against snowcoaches. But he did maintain during an interview that “when you sit in a 15-passenger van on a cold day, you cannot see out...” and that the coaches “rut” the snow-covered roads. He also acknowledged that heavy snowmobile traffic can create “washboard” conditions in the snow surface.

“As we note in many places, each one of these over-snow vehicles provides different kinds of experience for the visitor, and that’s really the important point here,” stressed Mr. Sacklin. “We’re not trying to say one is good, the other is bad. Each has some pluses, each has some minuses.”

From her viewpoint, Yellowstone Superintendent Suzanne Lewis says the growing mountain of research shows winter-use impacts, no matter the form of transportation, are lessening.

“Clearly, between 1995, ‘98, 2000, 2002, 2003, every year we gain more resource information through probably one of the most significant monitoring programs that exists in the Park Service to monitor the resource conditions,” said Superintendent Lewis. “And I think that ... when you examine the data, are we headed in the right direction, have we reduced in every one of those resource categories? I would tell you the data says ‘yes.’

“As we go forward in the next (EIS) analysis, what we are going to be looking at is it acceptable or unacceptable,” added the superintendent. “We’re basing these decisions -- at this point, they’re not decisions (they’re) construction of the alternatives -- based on long-term monitoring and continuing to move to achieve that highest and best resource condition that we can.”

Randy Roberson knows first-hand the comparisons that can and cannot be made between snowmobiles and snowcoaches. For years he has operated businesses in West Yellowstone, Montana, that rely on Yellowstone customers. He rents rooms and snowmobiles and offers snowcoach transportation in the park. (Full disclosure: His Yellowstone Vacations business is a Traveler sponsor)

On the question of fuel economy, Mr. Roberson said, “The Park Service asserts that snowcoach fuel economy averages 3-4 miles per gallon. If we use even the middle of this range -- 3.5 mpg -- and assume only eight visitors per coach when even the smaller of the modern snowcoaches have capacities of 14, and our average visitors-per-coach has been on the rise, then you see that the snowcoach over the same 60-mile roundtrip to Old Faithful uses 17.4 gallons, which is 2.18 gallons per passenger, which works out to 27 miles per gallon per visitor. That's in the case of the smaller coaches.

“With my larger coach,” he continued, “I always get 2-point-something miles per gallon. Always. I can take 30 passengers, but 18 is average. Now you really see the efficiency per visitor. Assuming just 2.0 mpg, the 60-mile-roundtrip to Old Faithful requires 30 gallons. With 18 passengers, that's 1.67 gallons per visitor, which works out to 36 miles per gallon per visitor.”

As for passenger comfort, things have changed over the years, said Mr. Roberson.

“The criticisms ... certainly applied, at one time, to old snowcoaches, although let me say that even many of them have been updated so that the criticisms aren't accurate even for them,” he said. “To give them due credit, those retrofits have combined history with modern technology. Here's the bigger point. For ten years, I've been building snowcoaches from the ground up, in every respect designing them for the winter environment of Yellowstone and the winter visitor's experience.

“That means they're heated, ventilated and have wonderfully large picture windows. My visitors have the advantages of large, comfortable seats, cozy temperatures, easy conversation and a tremendous vantage from which to enjoy the park's scenery,” said Mr. Roberson. “In all but the oldest of the park's snowcoaches ‘fogged’ windows are a thing of the past.

“I have no reason to say anything negative about snowmobiles. I continue to rent them,” he added. “But I can tell you that most visitors who really consider the benefits of one option versus the other are choosing snowcoaches and they are leaving the park very happy about what they saw, learned, and were able to talk about while someone else did the driving and they didn't have to deal with cold or wind or noise.”

Sadly, the world’s first national park, the one that arguably is better known and more revered than any other, the one found within the nation that launched the national parks movement, is mired in society’s technological hubris, one fueled by litigation. On one hand there’s the belief that technology can mitigate any and all impacts, and on the other is the promise of a lawsuit if you disagree. But how far should the National Park Service acquiesce in trying to please everyone? Should the agency, which is charged with preserving its properties "unimpaired" for future generations, allow "minuses," to borrow one of Mr. Sacklin's words, in the world's first national park?

Some would say there is a simple solution to the seemingly annual hand-wringing and judge-shopping over whether Yellowstone's winter travelers are to be born by snowmobiles or snowcoaches: Close the park’s interior from November to May. That’s right. Take a cue from Glacier, Crater Lake, Lassen Volcanic, and even Grand Teton national parks, all of which recognize that winter is a particularly harsh season, and put up “Road Closed to Motorized Vehicles” signs at Yellowstone’s west, east, and south entrances on November 1 and don’t take them down until May 1. Winterize the Old Faithful Snow Lodge just like the Old Faithful Inn and let the snows pile up deep on the steaming landscape. Let those who can snowshoe or ski into the park’s interior and enjoy its wintry wonders.

While that solution appears both outlandish and politically unrealistic, the Park Service had a recent chance to block snowmobiles from Yellowstone if it wanted to do so, as the 10th U.S. Circuit Court of Appeals recently noted in ruling on one of the recent filings in the matter.

In 1974, the appellate court noted, President Nixon issued an executive order “directing the Secretary of the Interior to establish policies for off-road vehicles on public lands ... the National Park Service adopted a default rule for all national parks: the ‘use of snowmobiles is prohibited, except on designated routes.' ... Under this default rule -- sometimes called the ‘closed unless opened’ rule -- the Park Service must promulgate a special regulation designating particular routes in a particular national park open to snowmobiles; absent such a rule, no snowmobiles are allowed.”

In short, when a Washington, D.C.-based federal judge in September 2008 threw out the park's winter-use plan because he found that it ran counter to both science and the Park Service's conservation mission, the Park Service could have banned snowmobiles by falling back to the default rule. Instead a federal judge in Wyoming took the stance that there were no regulations for winter-use in Yellowstone heading into the winter of 2008-09 and so ordered the park to fall back onto the 2007-08 regulations that allowed up to 720 snowmobiles if it could not come up with a temporary rule. The Park Service did not appeal that ruling by pointing to the default rule.

“... the default rule has always remained in place and it expressly forbids snowmobiles in national parks when there exists no other special regulation permitting them," the 10th Circuit noted. "The district court didn’t explain why the default rule failed to fill the regulatory void it perceived, let alone purport to adjudicate any challenge to the default regulation before effectively undoing its dictates.”

Short of banning all over-snow traffic outright, perhaps the best solution environmentally, but one also not likely to be accepted, is to simply open up the park by plowing the roads from Mammoth Hot Springs to Old Faithful and from West Yellowstone to Old Faithful and bring visitors in by shuttle bus. Alas, that option also is not without its flaws -- how would vehicles and wildlife coexist on roads bordered by 8-foot snow banks?

Sadly, for all involved, there likely will be no amicable resolution in the near future. Michael Yochim, in his book on the matter, Yellowstone and the Snowmobile, Locking Horns over National Park Use, concluded as much.

“... the agency’s lack of confidence in its ability to articulate and promote its own vision for winter use will continue to hamstring its protective efforts,” Mr. Yochim wrote. “For these reasons, we can expect to be arguing about winter use for many years to come; horns will remain locked for the foreseeable future.”