BILLINGS (LEE) - Noise from snowmobiles at several spots in Yellowstone National Park last winter exceeded goals set by park officials.

As in previous years, the loudest spots were near Old Faithful, along the groomed road between Madison Junction and the West Entrance and between West Thumb and Old Faithful, according to a recently released report.

While noise last winter was "substantially lower" than measurements taken during the winter of 2002-2003, there were also far fewer snowmobiles last year. Also, two-stroke engines were prohibited and all riders had to be in groups.

High noise levels from snowcoaches were also recorded last winter but not as often.

The report suggested that noise might be reduced by lowering speed limits, cutting down on the number of small groups and finding ways to reduce unnecessary idling and rapid acceleration.

John Sacklin, a Yellowstone planner, said the 2005-06 data will be used as the Park Service tries to draw up a long-term plan for snowmobiles and snowcoaches in the park.

For the longer term, park officials have been talking with manufacturers about ways to make the machines quieter.

The study of winter noise is part of an effort by the National Park Service to understand the effects of snowmobiles and snowcoaches in winter.

Last winter, researchers recorded sounds at five places between Dec. 21 and March 12.

They found that "oversnow" vehicles could be heard around Old Faithful 67 percent of the day between 8 a.m. and 4 p.m. On average, snowmobiles could be heard twice as often as snowcoaches.

At several places, including Old Faithful and some of the groomed roads, the noise exceeded the Park Service's goal of 70 decibels, roughly the sound of a vacuum cleaner being run inside.

Noise has been an issue in the long-running debate over the use of snowmobiles in Yellowstone and Grand Teton national parks. The Park Service has said that preserving natural quiet is an important part of its mission.

The Park Service is looking at a wide range of options in its third in-depth study of the snowmobile controversy. A draft of the latest environmental impact statement is expected to be finished and released to the public for comment later this winter.

In the meantime, Yellowstone will be open to snowmobiles this winter. The daily limit will be 720 snowmobiles. All will have to meet pollution and noise requirements, and all riders will have to be with a commercial guide.