Yesterday, a federal court delivered a win for conservationists when it overturned a Bush administration policy that would have opened Yellowstone National Park to unacceptable numbers of snowmobiles. Juliet Eilperin reports for The Washington Post:

U.S. District Judge Emmet G. Sullivan threw out the National Park Service's 2007 plan, calling it "arbitrary and capricious, unsupported by the record, and contrary to law." The administration rule would have allowed 540 recreational snowmobiles and 83 snow coaches a day to enter Yellowstone and Grand Teton national parks and the John D. Rockefeller Jr. Memorial Parkway. Sullivan said the plan violated the agency's mission statement.

Luckily for environmental advocates and park wildlife, the National Park Service did a good job making the case against its own policy. Had the Park Service chosen to ban snowmobiles and allow only snowcoaches (like public buses on the snow), it reports the adverse effects on air quality would be "negligible." Instead, under the 540-snowmobiles-per-day plan, the effects would be "moderate."

Another environmental consideration, "natural soundscapes," would also suffer under the plan to allow 540 snowmobiles per day, according to the Park Service itself. Furthermore, according to the Post, "Studies by the agency have found that snowmobiles in Yellowstone have frequently exceeded noise thresholds."

Choosing a policy option that is obviously not the most environmentally protective doesn't jibe with federal law. According to the Post, the act which created the Park Service "states that the agency's overriding mandate is to 'conserve park resources and values,' but it permits federal managers to 'allow impacts' as long as they do not impair the park's resources."

In his opinion, Judge Sullivan wrote, the act "clearly states, and Defendants concede, that the fundamental purpose of the national park system is to conserve park resources and values."

Sullivan's decision is the latest chapter in an ongoing saga. For at least a decade, the limit on snowmobiles in Yellowstone has been the subject of a pitched battle between conservationists and snowmobile advocates. Just before leaving office in Jan. 2001, the Clinton administration banned all snowmobile use in Yellowstone. The Bush administration was able to delay implementation until a federal court invalidated the ban in 2004 in a case brought by the snowmobile industry. The Park Service then instituted a temporary cap, which it then replaced with the 540 per day cap.

The International Snowmobile Manufacturers Association has already pledged to appeal Sullivan's decision, according to The New York Times.