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GLAD YOU ASKED: Salt switch started in 2009-10

Question: I always thought South Dakota mostly used sand on roads during the winter to treat state highways and interstates, but it seems like more salt is being used now. When did that change, and how does the state decide when and where to use salt? Is there any idea of how much salt the state uses or why salt has become more prominent in treating roads?

Answer: "The SDDOT has been using salt for many years," said Greg Fuller, director of operations for the South Dakota Department of Transportation. "In the past, the department used a mixture of salt and sand to treat our state highways. For the most part, the amount of salt used to treat roads is about equal to the amount of salt that was applied when it was mixed with sand."

Fuller said the SDDOT made the change to strictly salt in the winter of 2009-10, because in most cases, research showed that sand was not very effective in treating roads. And, in some instances, salt slowed the effectiveness of salt melting ice. The state typically uses 70,000 tons of salt per year.

"The salt is pre-wetted with salt brine as it is applied to the road surface," Fuller said. "This helps the salt stick to the roadway and jumpstarts the chemical reaction of the salt mixing with ice. The SDDOT does still use salt/sand mixtures in extremely cold conditions when the effectiveness of the salt is slowed and will also use salt/sand mixtures on hills, curves and intersections."

Fuller said sand alone cannot be used because it typically holds a lot of moisture and would freeze solid, making it hard to get out of the stockpile and through the sand applicator on trucks.

"We do also use other chemical applications such as magnesium chloride in lieu of salt, especially in extremely cold conditions as it melts ice at lower temperatures than salt does," Fuller said.