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Avalanche mitigation program reduces
number of winter closures on Idaho 21

Avalanche-related closures on Idaho 21 have been significantly reduced this winter through the use of explosives that bring down unstable snow before it slides and blocks the highway.

The highway, one of Idaho's popular winter recreation routes and host to the vast majority of the state's avalanches, is typically closed 60 days per year. But this winter – one of he hardest in recent years – Idaho 21 has been closed just 28 days, largely because of ITD’s preemptive measures.

"Given the heavy winter we have had this season, this is a positive sign that we will be able to reach our goal of reducing closure days by about half," said ITD lead avalanche forecaster Jon Barker.

Three primary methods have been used in this first-year program to deliver explosives:

An avalauncher (similar to a cannon) that delivers explosives into avalanche chutes
"Heliblasting" a process of dropping explosives from helicopters into avalanche-prone areas
When conditions warrant, ITD avalanche mitigation crews ski into areas and set charges by hand

Those triggers bring down the snow that has accumulated in the chutes, reducing avalanche hazards and allowing ITD crews to safely clear snow from the roadway. Bringing down snow accumulations enables crews to clear highways faster and more efficiently than if avalanches are left to occur naturally.

ITD received a special-use permit from the U.S. Forest Service to use the avalanche mitigation measures to reduce the potential threats to Idaho 21 between Grandjean Junction and Banner Summit. The 11-mile Canyon Creek section through the Boise National Forest, has 54 avalanche chutes and experiences about 90 percent of the avalanches that affect roadways.

The agencies worked together closely to ensure the area’s natural resources are protected in the development of a long-term avalanche control program.

The department also uses other tools to manage avalanche danger. Information is gathered using technology such as weather stations and snow-density testing to determine when avalanches are likely.

ITD recently purchased an additional weather station to provide the best possible weather-related information for avalanche forecasters.

"Our primary goal is to ensure safety," said ITD regional engineer Tom Points. "The expanded program also provides more reliable access to winter recreation areas along this highway and to the community of Stanley."