What are the limitations of road salt?

The minimum practical applications range for salt is a pavement temperature of 15 to 20 degrees Fahrenheit and above. While salt will melt snow and ice down to a pavement temperature of negative 6 degrees Fahrenheit, it can melt over five times as much ice at 30 degrees Fahrenheit as at 20 degrees Fahrenheit. Thus the effectiveness of salt is sensitive to small differences in pavement temperature. We attempt to apply only the amount required for temperature, time and use. Too little and the roadway will refreeze, too much is a waste of money and resources.

When the pavement temperature drops below 15 degrees Fahrenheit the effectiveness of salt is decreased significantly. At these lower temperatures, we typically cease straight salt applications and begin adding other chemicals to the salt such as calcium chloride or magnesium chloride that will lower the freezing point even further. Wind conditions must also be considered when deciding on whether to apply salt or other de-icing agents. As the temperatures drop and the snow becomes dryer, the wind can begin to blow the snow across the pavement. If there is a chemical residue left on the pavement from a previous salt application, blowing snow can be attracted to the residue and stick to the pavement creating hazardous conditions that would not have existed if no de-icing agents were previously applied.

This is why we are sometimes reluctant to apply salt or chemicals when the pavement temperatures are below 15 degrees Fahrenheit. The type of pavement can also affect the effectiveness of salt. For example, salt works better on new asphaltic (blacktop) pavements than on concrete pavement. The salt being used today typically includes other ice melting de-icing agents to increase its effectiveness at lower temperatures and to help it better adhere to the pavements. Adding other de-icing agents to the salt also reduces the number of applications needed. WisDOT is always looking for new ways to reduce the amount of chlorides needed to return the roadways to safe winter driving conditions.

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1. Who is responsible for my road?
2. How do I report a pothole/road issue?
3. How do I report damage to my mailbox?
4. How do I report a dead deer?
5. Why do we salt the roadways in the winter?
6. What are the limitations of road salt?
7. Why doesn’t the County use more sand?
8. Am I allowed to pass a snowplow?
9. Who determines when the snowplows are called out?
10. Why is it that I never seem to see a snowplow during a winter storm?
11. Why the difference in performance from storm to storm?
12. Why are you spraying water on the roadway on a perfectly clear day?