Rock or marine salt is used for treating roads, footways and cycle tracks and although it has a gritty appearance it is not "grit". The salt works by lowering the freezing point of moisture on the road surface.
Once trafficked into the road surface, salt can remain effective at temperatures of below minus five degrees Celsius providing it is spread before the start of these extreme sub zero temperatures. The salt is significantly less effective below minus 10 degrees Celsius.
The County Council uses a pre-wetted salt system on its road network. This system uses brine which is sprayed onto dry salt as it is discharged from the vehicles. With this system the salt becomes a more effective de-icing agent as it goes into solution faster and remains on the road surface longer than dry salt because it is not blown around by the wind. Less 'wetted' salt needs to be spread to give the same results as dry salt which is of benefit to the environment.
The white appearance of a well salted, dry road surface should not be mistaken for frost and it is normally safe for traffic movement. Often, even when it is dry, residual salt will itself attract moisture and can give the road surface a damp appearance, but the salt should prevent the moisture from freezing.
There is no such thing as an absolutely safe road surface during winter.
The presence of salt will not always guarantee an ice-free surface so concentration and care is always necessary when driving in winter.