Why roads may still be icy
Despite the high level of service provided, no guarantee can be given that roads will always be completely clear of ice or snow.
Ice may still be present in frost pockets/hollows and low-lying areas after the remainder of the network has thawed.
On average, forecasts are 90% accurate and in most winters this means that there are days when a road frost is not forecast but can actually occur.
It takes time for the salt to become effective after roads are salted.
Rain can wash salt off roads leaving them prone to re-icing.
In severe cold weather below -8C, even salt will not prevent roads from icing up.
If a road frost follows rain salting will normally start after the rain has stopped to avoid salt being washed away. Temperatures may fall by as much as 5C per hour and the wet roads may well freeze before the salt spreader has been able to salt them.
"Dawn Frost" - This occurs on dry roads and involves the development of early morning dew which falls on cold road surfaces and freezes on impact. It is impossible to forecast with any accuracy where and when it will occur. It is occurs particularly on commuter routes as the water vapour from exhausts falls on the road and freezes.
When rain turns to snow, early salting cannot take place as it would be washed away.
Treated roads can still therefore have icy patches and drivers should remain vigilant and aware of the need to drive carefully at all times especially when road frosts follow rain.
