Snow and ice on the roads

For road salting, we use rock salt, which works by lowering the temperature at which water freezes. The Colas depot can store 850 tonnes of rock salt.

Spreading salt on roads before or after snow falls does not prevent snow lying. It is traffic moving over the road, which crushes and mixes the snow and salt together, that melts the snow.  Sometimes we put salt on roads before the temperature falls below freezing to prevent frost.

We are aware that using salt can damage plants, trees and grass verges, cause water pollution and even change the properties of the soil. Colas take this into consideration when weather emergencies require salting the roads. As an alternative, we use grit, clear snow/ice manually or with the use of snow ploughs.

Find out about all winter maintenance carried out in Portsmouth, including gritting routes and salt/grit bin locations.

When we cannot salt the roads

There are some situations in which roads aren't salted, including:

• when it's raining - to avoid salt being washed away (wet roads can sometimes freeze before we are able to salt them)
• during rush hour traffic - the salt is worn away before it can take effect, and the gritters are unable to progress in the congestion
• if the temperature drops below -10c (14f), when salting is not so effective
• on roads which aren't often used - if there aren’t any passing vehicle tyres to mix the salt and snow together the snow will not melt
• if the gritter has difficulty driving down one of Portsmouth's many narrow roads due to parked cars