All Weather News

Why Do We Salt Our Roads?

24 Feb 2017, 7:41 am

If you have ever done any walking in a part of the country that uses salt to battle icy roadways– you’ve asked this very question.
The water from the melting snow creeps up your vulnerable pant leg, adding to the misery of standing in the snow and cold.
Only to have that water dry later on turning your cotton trousers into a rock-solid reminder of the weather outside.

It Melts the Snow

Simply put, the salt on the roadways melts the snow and ice. And the safety of millions is worth more than a few stiff pant legs.

We all know this already, but we are going to talk about this voodoo magic in scientific terms!

Salt acts to lower the freezing point of water.
A simple saline solution using table salt has the following affect of water.

  • A 10% solution drops the freezing point of water from 32°F to about 20°F
  • A 20% solution brings the freezing point of the water down to almost 0° F

So by spreading salt on the roadways during a storm, crews can actually lower the freezing point of water– therefore turning the ice and snow into a liquid.

This keeps drivers and pedestrians alike safe from the hazards of a slippery commute.
But what happens if it is too cold for a simple saline solution?

Not Your Mom’s Table Salt

If you’ve ever spent a day in a Chemistry classroom you probably know the chemical compound for salt is NaCl.
Sodium chloride, and for the most part, that is what is used to battle icy conditions on roadways. It’s both cheap and effective.

But the world’s most popular seasoning has a cousin that’s gaining popularity among DOT crews around the country.
MgCl2 — Magnesium Chloride
I’m going to keep this as simple as possible. Notice the little 2 after the chloride, thanks to the magic of chemistry and the way the solution forms with water the magnesium chloride is more effective than its simpleton cousin. (if you want the science feel free to message me on social media directly)
This means that a pre-storm brine or a sprinkling on an icy road can lower the freezing point of water much more effectively than its fry-topping cousin.

But What if its Still too Cold?

If temperatures drop low enough to where salt no longer works, sand is a great option!

Sand adds grip to a slippery surface and when combined with salt it can not only add extra traction, but also help melt the snow or ice when the temperatures rise.

The More You Know!

As with anything there are downsides.
I know each and every one of them just as well as the rest of you, so please don’t fill my inbox with complaints about your salty neighbor.

  • Salt is detrimental to ecosystems, the runoff brine can travel into the water supply hurting the local habitat and wildlife.
  • Salt destroys our cars. Just look at a 10-year old vehicle in the rust belt compared to one from the south or northwest.
  • Salt made my childhood hell. Rock-hard, white, crusty pant legs forced me to roll my cuffs– opening the door to ridicule from my ever-loving peers
  • Sand is blamed for poor air quality in many western cities. The finely ground particles are sent into the air creating poor air quality and an ominous haze.

That is just the tip of a much bigger iceberg, but for now the safety of millions of people each winter falls in the capable hands of salt.

For WeatherNation — Meteorologist Jeremy LaGoo

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