Why does salt melt ice on roads and sidewalks?

Salt lowers the freezing point of water through a process called freezing point depression. When salt dissolves in the thin layer of liquid water that exists on the surface of ice, it disrupts the ability of water molecules to form the organized crystal structure needed to stay frozen. This means the water needs to reach a lower temperature than 32°F (0°C) to refreeze. On roads, this causes ice to melt even when temperatures are below the normal freezing point of pure water. Regular table salt works down to about 15°F (-9°C), while other compounds like calcium chloride work at even lower temperatures. The salt doesn't generate heat; it simply changes the chemistry that allows ice to remain solid.