I think the liquid magnesium is for pre-treating the roads. We’ve been subjected to some freakish weather events in the last couple of years where the roads weren’t pre-treated & the temps got so cold, so suddenly that the de-icers weren’t effective. ‘Course the weather is always a bit freaky on I-81 between Tower City & Scanton.
From a montana state site:
“Materials Used for Winter Maintenance What is magnesium chloride?
Magnesium chloride is a salt compound extracted primarily from the Great Salt Lake, with added corrosion inhibitors, used to prevent or remove the build up of ice and snow on roads.
Magnesium chloride works like anti-freeze by lowering the freezing temperature of water and preventing ice from forming a strong bond to the road. It helps keep roads from becoming slick, improves safety and reduces accidents.”