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Why is Salt Used on Icy Roads?

By Samantha-Rae Tuthill, AccuWeather.com Staff Writer
December 11, 2013; 9:12 AM

Icy sidewalks and roadways can lead to disasters. Wintertime slick surfaces can cause a variety of problems, from a simple slip to a major car accident. To prevent property damage, injury or death, it's important for surfaces to be de-iced. This is usually done by distributing sand, chemical de-icers or salt over the ice. Of these three, salt is the most common.

The rock salt used on roads is the same salt that is used on your dinner table. The larger salt pieces are typically ground down to finer crystals before being placed on your supermarket shelves. Salt is collected by underground salt mines and then processed, packaged and distributed. The largest salt mining company in the United States, American Rock Salt, produces 10,000 to 18,000 tons of salt each day.

Peruvian salt mines. Photo by Frank Kehren

Salting roads works by altering the freezing point of water. Water with a higher salt content has a lower freezing point than water with less salinity. This accounts for the difference in Celsius and Fahrenheit temperature scales; 0 degrees C is the freezing point of fresh water, while 0 degrees F is the freezing point of brine solution that Daniel Fahrenheit mixed. Salting icy roads and walkways lowers the freezing point of the water that forms ice which leads to melting and prevents falling snow or rain from being able to freeze.

Though salt can be effective, it does have some negative impacts on the environment. Fifty pounds of salt, the equivalent to one large bag, can pollute 10,000 gallons of water. Melting ice and snow runoff that contains salt can pollute lakes and streams, which can have negative affects on plant and animal life. Fortunately, EarthGauge offers tips for helping to protect your water from the hazards of salt.

Photo by EarthGauge.net

First, you should shovel the area and remove as much of the snow and ice as you can yourself. When you apply the salt, only use it on ice and not on snow. This will require less salt to be introduced to the environment. You can also use 30 percent less salt if you add it to some water before applying it to icy areas. It's also important to keep salt away from your plants to avoid damaging them. The sodium chloride that makes up most salt is toxic to many forms of vegetation, choking out necessary nutrients they need to survive.

Photo by EarthGauge.net

There are many different compounds you can use to try and de-ice your area. One thing to keep in mind with rock salt is that some forms only work to certain temperatures. Sodium chloride, for example, doesn't work in temperatures below 15 degrees Fahrenheit. Magnesium chloride and calcium chloride, on the other hand, will work at lower temperatures.

For more information about de-icing options, watch this Weather Why video:

Salt and de-icer can have both good and bad effects during the harsh winter months. Meteorologist Justin Povick explains.

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