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Some Numbers To Keep in Mind When Reviewing Yellowstone National Park's Winter-Use Plan

Trumpeter swans, Yellowstone National Park, copyright Kurt Repanshek
Trumpeter swans drifing on the rivers of Yellowstone are one of the enjoyable sights of touring the park in winter. Kurt Repanshek photo.

For more than a decade the debate over how winter in Yellowstone National Park should be enjoyed has dragged on.

The National Park Service has gone back and forth with the political winds, calling back in 2000 for recreational snowmobile use to be phased out completely only to see the Bush administration drop that decision in favor of continued snowmobile use.

Legal battles waged by those who want continued snowmobile use and those who believe Yellowstone would be healthier without snowmobiles have prolonged the debate and led to a fistful of environmental studies -- environmental assessments as well as more complex and detailed environmental impact statements.

The latest comment period on the park's proposal for winter-use comes to an end next month.  Encompassing nearly 550 pages, this Draft Environmental Impact Statement on winter-use is a massive, complex document, one that challenges the lay person as well as the studied expert to be conversant on all its nuances.

Gibbon River, Yellowstone National Park
A thick white coat of snow is cut by the Gibbon River. Kurt Repanshek photo.

Along with technically exploring how best to move about the snowbound park, examining the impacts of snowmobiles and snowcoaches as well as looking at whether plowing of roads for wheeled traffic would be feasible, the study raises questions about the role of national parks, how best to conserve and preserve their resources, and how society views the parks.


Here are some numbers to keep in mind when studying this issue.


$10 Million+

Estimated amount the National Park Service has spent on winter-use studies in Yellowstone since 2000.

100 to 300...

Between 100 and 300 artillery rounds are kept on hand at Sylvan Pass for use in doing avalanche control to allow for safe passage by snowmobiles and snowcoaches coming into the park from the East Entrance.

...And One

According to a panel of experts convened in 2007 to discuss avalanche control work in Yellowstone, there is no other place in the National Park System "where NPS rangers are doing this kind of avalanche hazard mitigation or where this type of work is performed for a transportation corridor that is primarily used by over-snow vehicles."


Annual amount budgeted for avalanche control on Sylvan Pass.

Less Than 3 Visitors Per Day

Number of visitors entering the East Entrance via snowmobile and crossing Sylvan Pass last winter. There were no snowcoaches traversing the pass last winter, as no one bid on the contract.

Visiting Yellowstone by snowcoach
Snowcoaches stop to let riders out for photographs. Kurt Repanshek photo.

8 to 10

Park planners acknowledge that keeping Sylvan Pass safely open could impact wolverines, a slow-reproducing species that in December 2010 was listed by the U.S. Fish and Wildlife Service as a "candidate" species for Endangered Species Act protection.

Jeff Copeland, arguably the foremost wolverine expert in the United States, estimates that there are only 8-10 wolverines in Yellowstone.

Within the Environmental Consequences chapter of the park's DEIS, the planners note that "(B)ecause wolverine females give birth in mid-February and there is at least one known den in Sylvan Pass, there is a risk of disturbance of denning females and kits. Disturbance by OSVs and Sylvan Pass maintenance activities may result in lower quality parental care by female wolverines both prior to weaning at 10 weeks, and before young wolverines set off on their own, generally at around one year old."

At the same time, the planners concluded that "(P)opulation-level impacts on lynx (a threatened species) and wolverines under alternative 7 (the park's preferred alternative) are predicted to be long-term minor adverse."

From his vantage point, Mr. Copeland believes the odds are long that a wolverine would be killed directly by an artillery shell, but he does acknowledge that human disturbance could impact the species.

"I think the likelihood of one of their bombs killing a wolverine would probably be fairly remote. It would have to be a case of being in the wrong place at the wrong time, that kind of thing for the wolverine," he said. "The issue may be more about disturbance or displacement.”


As recently as 2009 a wolverine den was found on Sylvan Pass, according to the park's DEIS.

330 and 80

Guided Snowmobiles, Yellowstone National Park
Rows of guided snowmobiles at Madison Junction. Kurt Repanshek photo.

Under the park's currently preferred alternative in the winter-use DEIS, up to 330 snowmobiles and 80 snowcoaches would be allowed daily into the park for 45 days of the 90-day winter season.

254 and 63

"Average" daily number of snowmobiles and snowcoaches the preferred alternative would allow in the park, according to park officials.


The number of daily snowmobile numbers, above which, resource conditions in Yellowstone would be adversely affected, based on the Park Service's own science, according to eight former National Park Service directors. They added that placing a daily cap below 250 would be better for the health of the park based on the park's science.

The latest National Park Service study illuminates in detail that allowing Yellowstone’s current average of 250 snowmobiles per day to increase—to as many as 720 snowmobiles—would undercut the park’s resurgent natural conditions. Specifically, the study reveals that snowmobile noise would return to areas of the park where visitors are currently able to enjoy natural sounds and quiet. It demonstrates that exhaust would increase in Yellowstone’s air.  It sidesteps a recent recommendation made by Park Service scientists: that in order to minimize disturbance of the park’s wildlife, traffic should be kept at or below current levels, not expanded. -- March 2007 letter the former directors sent to then-Interior Secretary Dirk Kempthorne.


Average daily number of snowmobiles in 2008-09, the last winter NPS monitored the effects of oversnow vehicle traffic both on Yellowstone’s soundscapes and wildlife. Based on its monitoring, NPS concluded that: “The overall impact on the natural soundscape from oversnow vehicles was lower than the past five seasons, likely due to the decrease in daily average number of oversnow vehicles that entered the park; an average decrease of about 95 oversnow vehicles/day from last season.”

Regarding wildlife, NPS reported: “wildlife responses to motorized winter use were slightly lower for most species than in previous winters.”


Total number of snowmobiles (23,122) and snowcoaches (5,730) that could be allowed in Yellowstone during the 90-day winter season under the park's currently preferred alternative.

That total would surpass the levels of snowmobiles and snowcoaches seen entering the park during the winters of 2003-04 (24,481 vehicles), 2004-05 (20,565) and 2005-06 (24,379), the years monitored by Dr. P.J. White, a Yellowstone wildlife biologist, and his colleagues to measure wildlife impacts. In that study, the biologists recommended that over-snow vehicle levels be kept "at or below those observed during our study."

When questioned on the currently preferred proposal to allow nearly 29,000 over-snow vehicles entering the park each winter when Yellowstone's own biologists have recommended lower levels, park spokesman Al Nash responded that, looking at "average" traffic levels from the past two winters "the preferred alternative would allow both fewer snowmobiles and for fewer snowcoaches than we have allowed since limited, regulated use began."

The use of "averages" when discussing snowmobile numbers has not been supported by the courts.

In September 2008 when U.S. District Judge Emmet G. Sullivan struck down the park's most-recent winter-use plan he devoted more than five pages to wildlife impacts, and referred to Dr. White's studies and recommendations. He specifically took exception to the park's position that "there is no reason to expect that average use will increase over the current average of 260-290 entries per day."

"The Court is troubled by this argument, which persists throughout NPS’s briefs," wrote the judge. "There is no evidence in the record to support the assertion that future use levels will remain as low as those seen in the past three winter seasons."


These numbers reflect the sound levels of “best available technology” snowmobiles authorized for use in the park. The general trend since 2005 has not been in the direction of further reductions in the noise produced by snowmobiles entering Yellowstone, which NPS stated in the Federal Register that it expected based on assurances from the snowmobile manufacturers.

Instead, through the past six years the snowmobiles put forward by the industry for use in the park have generally become two to three decibels louder, with top noise levels above Yellowstone’s standard of 73 decibels.

In some cases, while there were initial reductions achieved in noise under the BAT requirements, numbers have begun to reverse. Some 2009 Bombardier models were measured at 70.1-72 decibels before inching backupwards to a range of 71.3 - 75.1 for 2011 models.

In its most recent soundscapes monitoring report, NPS attributes improved listening conditions for visitors at Old Faithful, not to technology, but to reduced traffic, stating: “The lower percent time audible value of the past two winters is likely due to a decrease in the daily average of about 100 snowmobiles/day.” 

Here’s what NPS expected, that hasn’t come to pass:

February 2003:

Old Faithful erupting in winter.
Old Faithful erupting in winter is a sight to see. Kurt Repanshek.

“NPS expects that snowmobile manufacturers will conduct ongoing research to continually improve sound and emissions in a line of available production machines.”
(Yellowstone Winter Use Supplemental EIS)

March 2003: 

“The NPS fully expects, and the industry has stated that, technological improvements will continue and that snowmobiles entering the parks will be even cleaner and quieter than the machines evaluated for the SEIS.”
(Yellowstone Winter Use Record of Decision)

December 2005:

“…there have been no improvements in air or sound emissions since 4-strokes were introduced in 2001.”     
(Text of NPS PowerPoint presentation in public process leading to development of the 2007 Winter Use Plan)

In the 2011 Arctic Cat and Bombardier models authorized for use in Yellowstone, certified sound levels are two to three decibels higher than those produced by Yellowstone BAT models six years ago. Both manufacturers’ machines produce sound levels in excess of Yellowstone’s standard of 73 decibels—reaching levels as high as 75.1 decibels.
(Snowmobile BAT list on Yellowstone Website)


There are seven alternatives in the DEIS. In addition to the park's preferred option, one calls for not allowing any motorized use, another calls for phasing out snowmobiles in favor of snowcoaches, and one proposes 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.

The proposals also call for continued use of "best available technology" (BAT) snowmobiles, 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. Under this proposal, 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.

Traveler clarification: The Traveler reported on May 5 that the Environmental Protection Agency in 2007 said a daily cap of 250 snowmobiles would be in the best interests of the park's health.

What the EPA said in its June 2007 comment letter to the park was that improvements had been made to "air quality, soundscapes, and wildlife disturbance" with traffic reduced by two-thirds of 'historic' use. Park Service documents have identified the 'historic use' number as 795 snowmobiles per day. One-third of that number would be 265 snowmobiles per day.

"Today, vehicle numbers are reduced by two-thirds compared to historic use, resulting in improved air quality and soundscapes as well as reduced wildlife disturbance," the EPA's letter said. "The combination of significantly reduced vehicle numbers and the use of BAT has decreased the predicted maximum carbon monoxide and particulate matter levels by about eighty-five percent.

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First I want to say I would rather visit Yellowstone in the winter for its quietness and solitude compared to the summer as the way it is there are extreme differences between the two seasons.

For an article reviewing the Yellowstone Winter Use Plan there sure isn't much said about the snow coaches and whether they meet the BAT requirements. A lot is put into the snowmobiles yet you remain silent on the snow coaches. We all know that the power requirements to run a vehicle as a wheeled vehicle are much less than when that vehicle has tracks on it serving as a snow coach. Why should the vehicle only need to meet emissions requirements as a wheeled vehicle when they have been converted to a tracked vehicle? Seems like you would want to meet the standards for what the vehicle is being operated as.

Anyway if you are reviewing the winter use plan there is still more to review.

This whole debate is because business owners who rely on park visitors for $$$$ want more and more vistors to Yellowstone they could care less about the impact the visitors have on the park.  These same business people want the federal spending reduced but for some one else not the parks that provide them $$$$.

Conversely John this debate is about those that want to shut down Yellowstone in the winter time to people to view the park by two methods of transportation, snowcoach and snowmobile.  Sure Kurt brings up valid points but it is all slanted at getting rid of snowmobiles. No mention that snowcoaches aren't the saint that groups trying to get rid of snowmobiles say they are.

Read Kurt's section on 28,852 where he compares total snowmobiles allowed to the averages of prior years. Then later in the section he writes that the courts don't support the use of averages when considering snowmobile numbers but he tries to anyway. I know that there is no way the maximum allowable number can be obtained as I have witnessed it on Jan. 1, 2010 when I couldn't get snowmobiles to go into the Old Faithful with an exchange student so we took a snowcoach. That day was still far from the maximum daily allowable but I couldn't get one from West Yellowstone so that is why I know you can't start trying to compare an average to a maximum. The maximum does set the line for an average though through the season.

Anyway John there is two sides to the story and some want to also eliminate the use of oversnow travel into the park and are silent on the noise issues of busses, trucks, and motorcycles in the summer.

YNP4everyone, curious, but where do I use averages when comparing snowmobiles to prior years? Those are Park Service numbers for entries for 2003-03, 2004-05, and 2005-06, not averages.

I also wouldn't say the above numbers story is "slanted at getting rid of snowmobiles." The numbers seem to support daily snowmobile entries at 250 or fewer per day, not an outright ban.

Kurt first I want to let you know that I respect you for your research into your articles but we have different opinions on the subject so we are looking at your article from a different viewpoint.

This quote is in your article, "The use of "averages" when discussing snowmobile numbers has not been supported by the courts." Then you talk about Judge Sullivan's comments in September 2008 about averages. At that time the daily cap was 720 snowmobiles per day and the past two seasons it has been at 318 per day so yes that will definately lower the daily average as less than half the amount would even be allowed in the park.

Three of your prior sections to the 28,852 section mentions "daily averages." That leads into your 28,852 section which starts off with 28,852 vehicles(23,122+5,730) which would be the maximum number of vehicles allowed into the park in the 2011-2012 winter season. The second paragraph then goes on to mention that level would exceed the 2003-06 season levels. You can't compare apples to oranges as the 28,852 is a maximum level and your other three years numbers are actual use levels derived from a maximum level which during that time period was 720 snowmobiles per day or 64,800 snowmobiles per season not counting snowcoaches. Again you need to keep the units behind your numbers so that you can show you are showing apples to apples which you weren't. If you compare maximum to maximum then you would see that the 28,852 is far less than the 64,800 plus snowcoaches that the maximum had been from 2003-06.

If you use your data from the NPS for those three years, wouldn't the three one year averages be the one and the same as the actual numbers that you listed? Then by adding the three together and dividing by three would give you the three year average or "level" as you call it in the second paragraph of that section?

I do know that the actual numbers are far below the maximum levels though. Your second pararaph tries to imply that the maximum will be reached next season but I would be willing to wager that the actual will be far below the maximum also next winter as I related in my prior comment that the park was far from the maximum. My family was unable to rent a snowmobile although the daily cap was far from being met to see the park so we spent the extra money and bought seats on a snowcoach instead so we know first hand you aren't going to approach the maximums using the current system with quotas on the different points of entry into the park.

My final comment about your 28,852 section is you state in the second paragraph that the maximum level would surpass the level (average) for the three years that you have listed. It would be a mathematical impossibility to have an average greater than the maximum so of course your comment is true but you present it as a fear that there will be far more snowmobiles next year than the 2003-06 seasons although the new maximum daily cap average of 254 is only 35 percent of the maximum of 720 during the years you mentioned.

Also your 254 and 63 section is a little misleading as you again changed the units as that is the average "daily cap" and not the daily average because when the cap is at the 110 they will not be allowing 170 in on those days so again you are inconsistant with your units.

Thanks for your time and I hope you understand how your actual use numbers are the ones used to find one, two, or three year averages because they weren't the maximums for those years like the 28,852 is the maximum for next year. Again for comparison sake you must compare like units.

YNP4everyone, the varying use of "average" and "maximum" levels is a reflection of the different comments and statements made on the park's winter-use planning efforts, not something I made up.

The citation of Judge Sullivan's comments concerning speculation on the park's behalf as to future OSV use levels shows his clear opposition to the park's use of "averages" in predicting future use, which is what Mr. Nash is doing when the preferred alternative states quite clearly that maximum daily entries of snowmobiles and snowcoaches could lead to 28,852 per season, a level above what the park's biologists recommend.

Will it? Based on most recent usage levels, likely not. But the judge does not seem inclined to approve a plan based on averages and hopes maximum levels won't be reached. As he put it, "There is no evidence in the record to support the assertion that future
use levels will remain as low as those seen in the past three winter

A question that's difficult, if not impossible, to answer is whether OSV usage would approach or even reach 28,852 per 90-day season. Has the recent winters' usage been reflective of uncertainty over winter-use regulations? Would numbers go up with more certainty in how snowmobilers could enjoy the park?

Let's not forget that for most of the winters during the past decade there was great uncertainty almost yearly over how many snowmobilers could enter the park, whether they could enter the park, whether they could go without guides, etc. No doubt more than a few simply decided not to visit Yellowstone and headed somewhere else.

The low Sylvan Pass numbers in Yellowstone are interesting.

It's worth remembering that Yosemite leaves its eastern entrance, Tioga Pass, closed for the winter and always has. Though some folks on the east side in Lee Vining get antsy when it's not opened by Memorial Day, it's a fact of life that most people seem to accept.

Thanks, YNP4everyone, for putting my issues with the numbers together so well.

I can assure you that no matter how you try, given the way the snowmobile "slots" are given out to gates and then to companies, you will never ever reach the max level for the day.  East gate never could reach its max.  The sole company that operates out of that gate doesn't have the snowmobiles to fill its daily quota.  The north gate is the same story.  That company doesn't ever rent the number of snowmobiles to fill that quota.  The extra slots are never filled.  South and West gates have multiple companies with multiple slots.  Though the different companies try to work together, the logistics of it are hard.  Say you call one company, and for one day they have two snowmobiles avalible.  You need four.  That doesn't work... You call two other companies, they each have one slot avalible.  That makes four, but unless you can get those three companies to work together, its a moot point for you.

As for the east gate, thanks for putting those numbers forth!  Close the east gate.  Its foolish to keep it open!

However, lynx is on the rise in Yellowstone.

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