Implementation of an anti-icing program in northern Idaho reduced winter maintenance labor hours by 62 percent and decreased abrasives usage by 83 percent.
Made Public Date


United States

Anti-Icing Success Fuels Expansion of the Program in Idaho

Summary Information

A 29-mile section of US Highway 12, from Arrow Bridge to the city of Orofino in northern Idaho, has always been a challenge for Idaho Transportation Department (ITD) winter maintenance personnel. The highway, which is located deep in a canyon, receives low to moderate amounts of snow and is prone to frost and black ice formation. The highway is particularly hazardous to motorists because slick pavement conditions can persist for long periods of time on sharp curves and in shaded areas. Extremely high quantities of abrasives applied to improve traction were only temporarily effective. In 1997, the ITD District 2 Maintenance Engineer decided to implement an anti-icing program to improve productivity and safety.

A chemical storage facility was installed in the maintenance yard to contain the anti-icing agent, liquid magnesium chloride. The storage facility included two 6,900-gallon tanks and an electric pump used for chemical circulation and truck loading. When inclement weather was forecast, a truck with a 1,500-gallon tank and a truck with a 1,000-gallon tank were used in concert with spray controls to pre-treat the highway with liquid magnesium chloride. Application rates varied from roughly 10 to 50 gallons per lane mile depending on the type of forecasted weather event. After initial application, maintenance crews regularly checked the status of four “indicator areas” along the highway. When frost on shoulder lanes began to migrate into travel lanes, the highway was retreated to ensure that the chemical concentration did not fall below effective levels.

A before/after study was conducted to determine winter maintenance trends over the period from Winter 1991/1992 to Winter 1999/2000. Yearly averages of labor hours, abrasive quantities, and accident frequency were calculated to compare the periods prior to and following inception of the anti-icing program in 1997. Comparison results are shown in the table below.

Comparison Table

Average Labor Hours
Average Abrasive Quantities
Average Number of Accidents
Before 1997
1475 m3
After 1997
247 m3
Amount Reduced
1228 m3
Percent Reduced

The US 12 anti-icing program was a tremendous success. Depending upon precipitation amount, humidity and pavement temperature; a single application of liquid magnesium chloride was typically effective for three to four days. The program has reduced labor hours by 62 percent, abrasives usage by 83 percent, and winter accident frequency by 83 percent. The successes of District 2 and other ITD districts have fueled expansion of anti-icing programs throughout the state.
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