Most public works agencies buy snow and ice control materials based on cost (45%) and performance (35%), rather than environmental impact (11%) and their affect on infrastructure (9%). Source: Transportation Research Board
When managers give equal weight to cost, performance, infrastructure, and environment, the tool software indicates how well selected deicers will meet department objectives at selected temperatures. Source: Transportation Research Board
Every winter, 22 million tons of snow and ice control materials are applied to North American roadways, but often the decision about which material to apply and in what amount has been more art than science.
Last year the Transportation Research Board published “Guidelines for the Selection of Snow and Ice Control Materials to Mitigate Environmental Impacts,” also known as NCHRP Report 577. Although some previous studies evaluated the effectiveness of various deicers and others documented their environmental impact, none integrated all those factors—until now.
The report is the result of a survey of 28 public works agencies across the United States and Canada.
Report 577 includes a free, downloadable decision-making software tool that allows managers to compare different purchasing and application scenarios by varying the “weight” of four variables: cost, product performance, the effects on infrastructure, and the impact on the environment.
The tool “generates a numerical evaluation that can be used to compare snow and ice control materials—automatically, objectively,” says Morton Satin, director of technical and regulatory affairs at the Salt Institute. “Each agency will have unique objectives and priorities that will affect their selections for the decision categories.”
For example, the tool prompts users to consider factors such as the presence of shallow drinking water wells, air quality concerns with particulates, concerns about whether sensitive vegetation grows within 10 meters of the roadway, or whether animals living near the roadway are sensitive to the product. Local planners don't need to protect sensitive fruit trees or rainbow trout if neither will be affected. Similarly, there's no need to worry about steel bridges if the local system has only wooden bridges.
The report evaluates 42 deicers—including sodium chloride, calcium chloride, magnesium chloride, calcium magnesium acetate, potassium acetate, and organic matter from biomass—for water quality and aquatic life, air quality, vegetation, drinking water, and soil structure. The effects on infrastructure include corrosion of concrete reinforcing (rebar) and atmospheric corrosion on exposed metals.
Sodium chloride is the preferred product above 12° F, for the 28 public works agencies across the United States and Canada that were surveyed for the report, followed by magnesium chloride and calcium chloride. Once temperatures drop below 12° F, sodium chloride and calcium magnesium acetate (CMA) lose performance benefits. Although potassium acetate (KA) is the preferred product, CMA also scores well at warmer temperatures.
“The two things that drive us are effectiveness and budget, but people are weighing environmental impact more and more,” says Mark DeVries, superintendent for the McHenry County Division of Transportation in Woodstock, Ill. “What's cool about this is that no matter where you are you can customize your choices, and you can defend those choices with data to your elected officials.”
DeVries, who's hosted several sessions at American Public Works Association North American Snow Conferences, believes the tool is the first of its kind. “Nobody's done exactly what (the Salt Institute) has done in letting you weigh all the possibilities,” he adds.