How does salt keep the road from getting icy?

(Lansing State Journal, February 1, 1995)

Bits of salt are commonly dumped onto roads and sidewalks to prevent them from becoming icy.

The salt acts in two ways. First, it helps prevent ice from forming in the first place. Salt water freezes at a lower temperature than pure water, so the salt helps prevent melting snow from refreezing.

Second, the salt bits can help break up ice that has already formed. When a car or truck drives over the salt bits, the weight of the vehicle pushes them downward and backward. These physical forces crack and shatter the ice. The friction also melts the ice and snow, allowing more of the salt to dissolve.

Sand and charcoal cinders are also used in some places to keep roads clear. But, they are generally not as effective as salt, because they do not significantly dissolve in the water.

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