While many were resting up the night before New Year’s Eve, state Department of Transportation workers Wade Tucker and Kelly Anderson were on the road, spraying down the region’s highways with magnesium chloride to prevent roads from freezing amid a forecasted frost.

The two maintenance technicians are part of the crews who spend winter nights de-icing roads before the morning commute. Their main tool is magnesium chloride, a mix of chemical salt and water that quickly melts through ice. The de-icer is purchased in bulk and stored at stations along the state’s highways.

Tucker and Anderson begin their nights at a maintenance yard in Warrenton. They load large yellow tanker trucks with up to 1,600 gallons of the de-icer at a time and fan out on loops along U.S. Highway 30 east to Westport, U.S. Highway 26 east to the Elderberry Inn and U.S. Highway 101 south to the Tillamook County line, along with state highways snaking through the forests. Spraying at a rate of 20 to 30 gallons per mile from a line of sprinklers near the rear bumper, they can put out up to 6,000 gallons in one night.

“We apply mag chloride as a pretreatment to keep ice from forming on the highway due to wet pavement falling below 32 degrees, frost, freezing fog, and in cases, freezing rain,” said Mark Buffington, District 1 manager for the state transportation department.

The mixture — referred to by road managers as “mag” — is applied when temperatures range between 25 and 38 degrees Fahrenheit, with no rain forecasted in the next 24 hours. Transportation workers deploy sand when packed snow and ice already cover the highway. While the de-icer has been invaluable in helping keep highways passable, Anderson said it can also give drivers a false sense of security.

“They see us putting out the de-icer, and they’re flying,” he said. “But they don’t realize it might be really cold, or there might be a bad batch.”

Tucker and Anderson cautioned against driving at all when there is freezing rain, or when temperatures fall dangerously low, and advise drivers to stay well away from the trucks deploying magnesium chloride, a highly corrosive substance over time.

Last winter, more than 430,000 gallons of magnesium chloride was spread on Northwest Oregon roadways, along with about 9,000 cubic yards of sand. The state has used the de-icer for nearly 20 years, Buffington said.

Oregon has eschewed the more common rock salt and salt brine used by neighboring states to de-ice roads because of the harm to water quality and aquatic life as residual chlorides drain into streams. Evidence has been scant, however, as to the environmental friendliness of magnesium chloride. The state has recently experimented with rock salt on especially treacherous stretches of road near borders with California, Idaho and Nevada.

Even with corrosion inhibitors mixed in to limit damage to property, magnesium chloride is not without its own dangers.

The results of a study published in 2015 by the state and Alaska University Transportation Center showed magnesium chloride can weaken the state’s bridge decks and piers after 10 to 20 years of treatment, increasing the possibility of premature failure. The damage is not visible from the road surface, but core samples showed magnesium chloride’s ability to weaken the elasticity of concrete in absorbing the force and weight of cars driving overhead.

“It could be catastrophic,” Xianming Shi told The Bend Bulletin in a 2015 story about the study. “I think it’s important to educate the public on what the risks are.”

Shi recommended washing down bridges at the end of winter, because most of the damage occurs in summer, and said alternate mixes of Portland cement could mitigate damage. State transportation spokesman Dave Thompson told the paper at the time that the state maintained the practice of sealing bridge decks prior to winter, but hadn’t created a plan in response to the study’s findings.

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