BILLINGS, Mont. - Snowmobiles and snowcoaches in Yellowstone National Park are still noisier at times than thresholds set by park officials.

A draft report on wintertime noise in Yellowstone, released late last week, said the consistently loudest spots last winter were near Old Faithful and along the groomed road between Madison Junction and the West Entrance.

The Park Service report said conditions are quieter than in years past but more should be done to reduce noise in the winter.

Options include reducing speed limits, phasing out two-stroke snowmobiles used by Park Service and concession employees, and doing something about the older, louder Bombardier snowcoaches still in use.

Al Nash, a Yellowstone spokesman, said those ideas will be considered as the Park Service develops a final long-term plan meant to govern winter recreation in the park.

Noise is one of several issues in the long-running controversy over snowmobiles in Yellowstone. The Park Service has said preserving natural quiet is an important part of its mission.

A switch to four-stroke engines several years ago helped reduce noise and pollution, but park officials are still contending with those issues as they develop a final environmental impact statement.

Earlier this year, the Park Service released a draft plan for Yellowstone, saying its preferred alternative - which is nearly identical to a temporary plan in place since 2004 - would be to allow 720 snowmobiles and 78 snowcoaches a day into Yellowstone.

The machines would have to meet noise and pollution standards, and snowmobilers would have to be with commercial guides, according to the proposal.

A final version is expected to be completed before the Dec. 19 start of the winter season in Yellowstone.

Nash said the latest plan is benefiting from three years of air and noise monitoring data instead of relying more heavily on computer modeling.

"This is the kind of information that we really didn't have to go into the previous process," Nash said.

Much of the focus has been on finding out how much of the time snowmobiles and snowcoaches can be heard.

The most recent study was done between Dec. 20, 2006, and March 11 when, on average, 30 snowcoaches and 299 snowmobiles came into the park each day.

Near Old Faithful, snowmobiles and snowcoaches could be heard 68 percent of the time between 8 a.m. and 4 p.m., roughly the same as in previous years under the temporary plan. Snowmobiles could be heard 61 percent more often than snowcoaches, the study said.

Around Madison Junction, snowmobiles and snowcoaches could be heard about 59 percent of the time.

Researchers found repeated incidents where noise levels exceed the Park Service's maximum threshold of 70 decibels, which is roughly the sound of a vacuum cleaner being run inside.

Those high readings were recorded near Old Faithful, on the road between Madison and the West Entrance, and between West Thumb and Old Faithful.

Although snowmobiles could be heard more often, snowcoaches and Park Service snow groomers had the highest sound levels, the report said.

Still, the report said, the noise was "substantially lower" than the 2002-03 winter, the last year when snowmobile use was unregulated.

"Any visitor, especially to places like West Yellowstone, doesn't need sophisticated monitoring equipment to realize things are better," Nash said.

The Environmental Protection Agency, though, said the Park Service's latest plan still doesn't do enough to preserve quiet places in the park or protect wildlife and employee health.

The EPA in June said earlier noise studies apparently tested volumes only inside the kiosks where park rangers usher snowmobiles and snowcoaches into Yellowstone.

"If some employees work outside the kiosk - as they did in the past - it is possible that noise could still represent a significant hazard for them," the EPA said.