Winter motorists could be forgiven for feeling at least some small amount of trepidation when negotiating a notorious 11-mile stretch of state Highway 21 between the rural communities of Stanley and Lowman.
Following the winding curves of cascading Canyon Creek, the highly scenic but remote stretch of road passes through the narrow terminus of two formidable mountain ranges, the Sawtooths to the east and the northern end of the Boise Mountains to the west.
Pouring in from both sides along the highway is a total of 54 highly active avalanche chutes. This veritable gauntlet between mileposts 105.5 at Banner Summit and 94.4 near the Grandjean Road turnoff makes the stretch of roadway one of the most highly avalanche-prone highways in the country.
Standing guard at both sides of the stretch of highway are large red and white-colored warning gates, which highway officials can drop at a moment's notice when avalanches threaten.
Because of the area's high avalanche proclivity, officials with the Idaho Transportation Department have for many years taken a cautious approach to maintaining the stretch of road during the cold winter months. In most winters, the threat of avalanches has kept the highway closed for an average of 60 days.
However, beginning this winter, state highway officials hope to cut that figure in half using a number of advanced avalanche mitigation measures.
Standing before a small crowd of Stanley residents on Dec. 5, Tom Points, Region 2 engineer with the ITD, explained the series of avalanche mitigation measures the department is set to implement this winter.
Using a combination of different-sized explosive charges, Points said they hope to cut the number of days the highway is closed down to 30 and in doing so make traveling to Stanley in the winter a more reliable bet. He said avalanche experts employed by the department will be deploying the charges from large gas-compressed avalaunchers, from the air by helicopters and by hand from protected sites.
Points said that beyond the high number of avalanche chutes, factors making the avalanche danger even worse along the stretch of road are the steepness of slopes in the area and the impacts associated with the 2003 Canyon Creek Fire, which burned on both sides of the highway.
Pointing to a 1996 avalanche that dumped 45 feet of debris on the roadway as just one example, he said keeping the highway open has always been a struggle.
"We're always fighting Mother Nature on this one," he said.
Keeping a close watch on the weather inside the canyon are three separate weather stations. Combining the up-to-the-minute weather data these weather stations provide along with hand-dug test pits, highway forecasters will be able to make accurate assessments of the avalanche danger, Points said.
"After that, we ask is there an avalanche risk," he said.
And if the risk is high, a two-person team from the highway department based out of the nearby community of Lowman will implement the avalanche mitigation measures.
"This is a continuous process," Points said.
However, he said that foremost in the highway officials' minds will be the safety of the department workers—both the road clearing and avalanche mitigation crews—as well as the traveling public.
"We've never lost anyone in this canyon (to avalanches) and we intend to keep it this way," he said.
So far, the actions taken to get the program where it is today has cost the ITD a total of $1 million, Points said. This includes the initial capital costs to purchase equipment, survey work by a Canada-based avalanche consultant and a successful trial run of the mitigation measures last winter, he said.
He said that the Highway 21 avalanche program will cost the department about $200,000 per season.
So what will that large annual expenditure achieve? From the perspective of Stanley officials, quite a lot.
In the past, many travelers who might have considered coming to Stanley for the weekend for winter recreation have not done so because they couldn't be sure that the highway would remain open for their return home, Stanley Mayor Hannah Stauts said Tuesday. Many of these travelers are from the Boise and Treasure Valley areas, Stauts said.
"It makes it an unpredictable route," she said.
Stauts said this has been a significant drain on the Stanley economy during the winter. She said the only reliable alternative route for Boise motorists has been to go through the Wood River Valley and over Galena Pass to access Stanley during the winter.
"If we don't have Highway 21 open you're looking at adding two hours to your trip both ways," she said.
Stauts said having Highway 21 closed so often has also been a drain on Stanley residents wishing to travel to Boise for things like affordable shopping, medical care and for visiting friends and family.
Making the decision to close or keep the highway open will be the highway department's lead avalanche forecaster for the area, Jon Barker. Barker will be based out of Lowman.
To determine if the road should be closed, Barker said he and his assistant forecaster will go to the field to apply their explosives.
Slopes that hold after a charge has been detonated make keeping the highway open more likely, Barker said.
"Yeah, we don't need to wait two more days," he explained.
Of course, closures will be needed at times, Barker said. However, those closures shouldn't last as long as they used to because of the avalanche mitigation measures.
"We're not in a waiting game for (snowpack) settlement," he said.
A lot of Barker's work will include actually skiing in to remote sites above the highway to test for slope stability and possibly set off hand charges, he said.
"Pretty much skin up to anywhere you want to work," he said.
Barker, who has worked in other high avalanche danger areas including Snoqualmie Pass in Washington state, said the 11-mile stretch along Canyon Creek is unique in that it doesn't have any easy way access points other than the highway itself. He pointed out that beyond both sides of the highway are large areas of roadless high country.
Barker said most other notoriously avalanche-prone highways around the country have easier accesses from nearby ski areas, cat tracks or forest roads.
"There aren't those options here," he said.