Practical monitoring of the amount of salt spread on the road surface for de-icing purposes is technically difficult, especially if it has to be done in a commercially viable way. Possible solutions to this problem are discussed. As it has become customary to refer to the freezing temperature of a salted road, the physical meaning of such a temperature is scrutinised. It turns out that the meaning and the definition of freezing temperature are not clear, and that it also does not have the significance that is often associated with it. Some experimental results of salt measurements on a road are presented.