Why is salt placed on roads in the winter?
In the places where there is too much of snow and ice in the winter on the roads there the highway departments use to sprinkle the salt over the ice to clear the roads. They use salt for this purpose because salt has the tendency to lower the freezing and melting point of water so in this case we use the idea to lower the melting point of ice so that it can melt easily.
Water changes to ice at a temperature of zero degree Celsius/32 degree Fahrenheit. So when salt is added to the water the temperature of freezing lowers. If we add 10% salt to the water then it will freeze at -6 degree Celsius/20 degree Fahrenheit. So when salt spreads over the ice on the road it dissolves in the liquid water present with the ice and hence decreases the freezing point of ice and it immediately starts melting the ice which is in direct contact with the salt grain and further allows the other parts of ice to melt. This whole process will not work if the temperature of the road goes below 15 degree Fahrenheit then the salt will not happen to melt the ice present on the roads. Salt will not be able to dissolve in the ice at this temperature. Here another thing which can prove helpful is to sprinkle the sand over the ice.
No doubt using salt on the snow covered road will be helpful but at the same time salt is a corrosive agent who eats the roads and the vehicles running over them. Secondly use of large amount of salt can be toxic for the environment. Thirdly salt is not expensive but using it in the large quantities over the roads will be a wasteful thing. Earlier the production of salt was not much but now it has increased a lot because 51% of the total salt production is used by the cold countries.