Salt lowers the freezing point of water. The greater the concentration of salt, the lower the freezing point, although there is a limit of temperature below which salt will not melt ice. This is well below usual winter temperatures in the British Isles. Melting begins on contact when salt is spread on ice or snow. This produces water, dissolving more salt and producing further melting.
Heat is absorbed in the melting process - the latent heat of fusion.
This heat must be absorbed and the rate of melting will depend on the surrounding air and ground temperatures. Other influences on melting rate are the particle size of the salt and the amount of mixing caused by traffic. How Salt is Used When ice and snow are expected, trained winter maintenance teams are mobilised to apply salt at the right rate on planned salting routes. Salt applied before ice or snow occurs produces safer conditions, using less salt. This is called precautionary salting.