The Utah Department of Transportation is charged with the responsibility of keeping state roads safe, and part of that responsibility includes forecasting and preventing snow avalanches.

A system known as the Highway Avalanche Hazard Index has been developed to give a numerical value to the potential snow avalanche threat.

Some of the roads in Utah affected by Snow Avalanches include SR 158, Powder Mountain; SR 190, Big Cottonwood Canyon; US 189, Provo Canyon; US 40, Daniels Canyon and SR 92, American Fork Canyon.

Steep terrain, heavy snowfall, and snow-pack combine to make those Utah roads prone to snow avalanches. But of all the roadways in Utah that are threatened by snow avalanches, the most frequently occurring hazard is on Little Cottonwood Canyon – SR 210. In fact, Little Cottonwood Canyon Road has one of the highest Avalanche Hazard Index ratings in North America.

A system known as the Highway Avalanche Hazard Index has been developed to give a numerical value to the potential threat. The  rating helps planners and administrators “have some understanding of what motorists face on mountain corridors,” says Liam Fitzgerald, UDOT’s Avalanche Forecaster.

A number of factors are combined to determine that numerical value, including snowfall abundance, terrain steepness and traffic volume. Comparing Little Cottonwood Canyon Road with other well known mountain roads gives some perspective: Red Mountain Pass in Colorado has a rating of 126, Rogers Pass in Canada is rated at 174 and Little Cottonwood Canyon Road is rated at 766.

Little Cottonwood Canyon has in part been shaped by avalanches. Avalanches influence vegetation patterns and in turn, vegetation influences erosion patterns forming gullies. Gullies then direct debris further influencing tree growth. Terrain in different parts of the canyon leads to different types of avalanche problems.

Some terrain is very steep and rugged which results in more frequent avalanches usually involving more recently deposited layers of snow. In other sections of the canyon where terrain is more open and less steep, fewer avalanches tend to occur but those occurrences often involve older layers of snow and may cover a wider area.

Although most of the time avalanche forecasting and control efforts allow for safe travel on the canyon roads, upon occasion, naturally occurring avalanches reach the canyon roads while they are open.

Information about back-country safety can be obtained by clicking under the Salt Lake City link on the Avalanche Center’s Web site, www.avalanche.org.

This post is based on a presentation given by Liam Fitzgerald, the Avalanche Forecaster for UDOT.

2 thoughts on “RATING ROADS”

  1. Gary Whitton

    I would be interested in knowing where the image for this post was taken. What canyon and mountains are we looking at?

  2. Becky Parker

    The photo was taken from Maybird Gulch by Adam Naisbitt one of our Avalanche Forecasters. It is of the north side of Little Cottonwood Canyon with the Salt Lake Twins on the left and Superior on the right.

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