Salt Questions · Science, chemistry & environment
Why does salt melt ice on roads in the winter?
Short answer
Salt dissolves into the thin layer of water that's always on ice, forming brine. Brine has a lower freezing point than pure water, so the ice melts. Road salt works best down to about −9 °C (15 °F); below that it works slowly, and it can't melt ice at all below about −21 °C (−6 °F).
How salt performs on roads
- 1Eutectic −21.1 °C (−6 °F)
- 2Effective to ≈ −9 °C (15 °F)
- 3Water freezes 0 °C (32 °F)
Freezing-point depression
Dissolved salt splits into ions that get in the way of water molecules locking into ice crystals. To freeze, the water has to get colder. This is called freezing-point depression. Salt doesn't heat the ice; it changes the temperature at which water can stay frozen.
Temperature limits
- 0 to −9 °C (32 to 15 °F): salt works well.
- −9 to −21 °C: it works increasingly slowly.
- Below −21.1 °C (−6 °F): the lowest point of the salt-water mixture (the eutectic point); salt can't melt ice.
Brine and pre-wetting
Road crews often spray brine before a storm (anti-icing) so snow doesn't bond to the pavement, which uses less salt than melting ice after it forms. Our road salt calculator estimates quantities and chloride loads.
Related on The Salt Almanac
More science, chemistry & environment questions
- Is salt an element, a compound, or a mixture?
- How does salt water conduct electricity?
- Why is the ocean salty but rivers are fresh water?
- What temperature does salt water freeze at?
- How do salt mines form underground?
- Why does salt prevent ice from forming at 32 degrees?
Cite this page
For school projects and reports. Teachers often prefer the original sources too: see the list below.
The Salt Almanac. (2026, November 8). Why does salt melt ice on roads in the winter. https://saltalmanac.com/answers/why-does-salt-melt-ice-on-roads-in-the-winter
“Why does salt melt ice on roads in the winter.” The Salt Almanac, 8 Nov. 2026, saltalmanac.com/answers/why-does-salt-melt-ice-on-roads-in-the-winter. Accessed [today's date].
“Why does salt melt ice on roads in the winter.” The Salt Almanac. Last modified November 8, 2026. https://saltalmanac.com/answers/why-does-salt-melt-ice-on-roads-in-the-winter.
Original sources
- Wikipedia. Freezing-point depression. https://en.wikipedia.org/wiki/Freezing-point_depression
- Wikipedia. Brine. https://en.wikipedia.org/wiki/Brine
- Corsi SR, et al. A fresh look at road salt: aquatic toxicity and water-quality impacts. U.S. Geological Survey, 2010. https://www.usgs.gov/publications/fresh-look-road-salt-aquatic-toxicity-and-water-quality-impacts-local-regional-and