We use 6mm crushed rock salt, we do not use grit. It melts ice or stops it from forming on road surfaces.
This is spread by our purpose-built gritters that have a 'spreader' at the back. This gives an even layer of salt across the road at a controlled rate.
Gritting vehicles can also be fitted with snow ploughs, when needed.
How salt melts the snow
Traffic needs to drive over a gritted road in order to grind the salt and activate it.
Salt spread on the roads has little effect on melting snow, on its own. We need vehicles to drive on it to mix the salt with the ice and snow. This creates a saline solution that has a lower freezing point. Only then will the snow and ice melt.
In the concentrations we use on our roads, rock salt is less effective at temperatures below minus five degrees centigrade.
When we grit a road, further snow fall can lay on top of the road. This covers the salt, which can make it look like we have not gritted.
Gritting in rainy conditions
You may see us gritting when we have rain, but the forecast road temperature is below zero. Here we must treat roads to stop ice forming.
These are tricky conditions, as the rain can wash grit away or reduce how well it works. This can then lead to ice forming.
You may also notice this when we are treating snowfall on our highest roads. This can fall as rain at lower levels, with the chance of ice forming.