Why do we put salt on winter roads?

Waking up and seeing snow outside is one of the most exciting feelings for people across the world (sorry to everyone in Arizona). Snow means no school for kids, and no work for adults, which means free time to build snowmen, participate in fierce snowball fights, and drinking hot chocolate all day. 

Another characteristic of snow days is the prevalence of large trucks on roads, spreading salt everywhere. While snow days do offer a lot of fun, freezing temperatures and ice can make driving dangerous, which is why these salt trucks are extremely important for winter roads. 

The salt these trucks put on roads is very similar to normal salt in a family’s pantry, but serves a much different purpose. The salt dumped on roads actually prevents ice from forming, making driving safe for commuters and public transportation. 

Pure water freezes into ice at 32 degrees Fahrenheit (0 degrees Celsius), but adding salt into the mix drops the freezing point. The new salt-water solution has a freezing point closer to 15 degrees (-10 degrees Celsius), making it much harder for roads to freeze over. Of course, this means that extremely cold climates won’t receive the benefits salt provides, as the salt-water will still freeze. 

However, it’s important that the salt is mixed with water, as already formed ice isn’t affected. Ice melting due to the ground’s warmth and cars driving over it allows the salt to work its magic, and prevent the water from turning back into ice. (This is the same reason why bridges freeze much easier, as there is no earth beneath them to warm up and melt the ice)

The practice of putting salt on roads is greatly beneficial for humans trying to travel, but does have negative impacts on the environment. The salt on the roads doesn’t simply disappear, and instead runs off into other bodies of water, or into nearby soil, harming plants and animals. There are environment-friendly versions of salt, so look forward to seeing colored salt in the future – thanks to organic material like beet juice and molasses being mixed in. 

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