Why are treated roads sometimes still icy?
No matter what we do we cannot be sure treated roads will always be completely clear of ice or snow.
This is because:
- in heavy snowfall, salt treatments only work on roads with heavy traffic
- it takes time for the salt to work after roads are salted
- rain and running water can wash salt off roads leaving them prone to re-icing
- in severe cold weather (below –5°C) salt will not prevent roads from icing.
- if freezing conditions follows rain, salting will normally start after the rain has stopped to avoid salt being washed away. Temperatures may fall by as much as 5°C per hour and the wet roads can freeze before the gritter has been able to salt them.
- dawn frost occurs on dry roads where early morning dew condenses on cold road surfaces and freezes on impact. It is impossible to forecast with any accuracy where and when this may happen.
- when rain turns to snow during the rush hours, early salting is washed away and gritters are unable make progress due to traffic congestion
- there may be water on the road for other reasons. These could include a water mains leak, vehicles being washed or windscreens having water poured over them to melt the ice. These quantities of water will result in ice forming if the road surface temperature is below zero degrees. The council treats major water leaks as soon as it can.
- over a season, weather forecasts are approximately 90 percent accurate. In most winters, this means that there are several days when a road frost is not forecast but will still occur.
Treated roads can still have icy patches and drivers should be aware of the need to drive with due care at all times, especially when road frosts or freezing temperatures follow rain.