Q: What kind of substance is applied to the local roads during freezing weather? Is the liquid mixture salt or something else? What kind of damage can it cause to cars?
A: Rust. That’s the one word answer. As to what the substance is, that answer is more complicated. But rather than turn this into a chemistry lesson, let’s take a short trip back in time, to the Great Seattle Salt Debate of 2008.
Maybe you remember; the city of Seattle had decided to abandon salt as a treatment for icy and snowy roads, committing instead to using sand. And then the city was hit by the biggest snowfall in a decade. Many roads were impassable, leading to a collision that made international news when two buses full of students slid down a hill and crashed through a concrete barricade, the front quarter of one bus dangling over I-5 thirty feet below. (By magic, luck, physics or divine intervention there were no serious injuries.) In the aftermath, the city switched back to using salt, or other salt-ish chemicals. Some folks speculate that the mayor’s no-salt stance cost him the next election.
I share that story to point out that in many situations there isn’t a perfect solution. And when I say “solution” I mean both the answer to a problem and the homogenous mix of two or more substances. In a perfect world we’d have a deicer that was effective, environmentally friendly, didn’t leave behind any residue or sediment (we’re looking at you, sand), didn’t cause corrosion to vehicles and was cheap to apply. In real life, that product probably doesn’t exist. Picking a deicer means making compromises, and choosing between making the roadways safe right now and the possibility of corrosion in the future, transportation departments pick safety.
That’s not to say that all deicer is equally corrosive. There are a lot of options besides Sodium Chloride (regular old salt). Choices include Magnesium Chloride, Calcium Chloride, Calcium Magnesium Acetate and more. They come in lots of different mixtures, some with corrosion inhibitors added. Many are mixed into a brine to create a sprayable liquid. Some deicers offset the amount of salt or other chemicals with vegetable-based additives. A common one is beet juice. There’s some science involved in picking the right deicer for the situation.
I checked the lists from several road departments in Washington and all of them included chemical-based deicers as an option. Washington DOT describes their snow and ice strategy on their website, and it includes salt as one possible tool. We don’t see too many vehicles rusted out from road salt on the west coast, because we don’t have that much snow compared to places like Michigan or Vermont. But deicer does cause corrosion to vehicles. A study by AAA found that corrosion caused by deicing was responsible for $3 billion of damage a year to vehicles in the US.
Corrosion isn’t just an aesthetic problem. Lots of the parts under your car are metal – brake lines, tie rods, the frame. You know, important things that make your car safe. To combat corrosion, wash your vehicle regularly, including the undercarriage, during the time of year when deicers are applied to roadways. And the best option, if you can choose it: don’t drive when roads are icy. When road conditions get worse, crashes increase. You can protect your car and decrease your risk by eliminating unnecessary trips in snowy and icy conditions.
As I was writing this I did think of low cost, environmentally friendly way to clear the roads. Can we just take all the kids doing remote schooling during the pandemic and tell them that their PE class is going to be shoveling snow?