How gritting works

Gritting does not mean that the road surface will become ice free. The process works by:

• Turning the ice or snow surrounding each granule into a saline solution which has a lower freezing point than water. 
• The action of traffic helps the salt to be more effective by moving it around and eventually melting the ice or preventing ice forming. 
• Salt is less effective on road surface temperatures of greater than minus 5°C and so will take longer to work in these conditions. 
• It best works to combat snow when snow depth is less than 40mm deep and again only when traffic moves the salt around. 

Why roads could still be Icy

To work effectively, salt needs vehicles to drive over it. Vehicles grind the salt into smaller particles to help it spread across the road. 

This means:

• The more traffic a road has, the quicker it will take effect.
• Less effective when there isn't as much traffic. 
• Less effective when there is a lot of snow. 

Continued rainfall or sleet can wash salt off roads. This leaves them prone to:

• Ice reforming on the road surface.
• If the rain turns to snow, any earlier treatment will be less effective or washed away entirely.

Water begins to freeze at 0°C and the presence of Salt helps to prevent water from freezing. However:

• Salt loses its effectiveness between minus 5°C and minus 8°C.
• And all effectiveness from minus 10°C

Lastly, if weather conditions are extremely severe, access to the road network is not always possible - even for our gritting crews. Also, it is not possible to grit roads in heavy traffic.