The winter service includes precautionary salting of all carriageways and the more important footways in advance of forecast ice and snow.
For the last two winters, 2006-07 and 2007-08, pre-wetted salting has been used on the North West and South West Units and for this past winter, 2007-08, on all four Trunk Road Units.
During the period 1 November to 31 March, winter patrols operate on 19 routes from midnight to 8 am and during the day if conditions require this. These routes, which are mainly on the older parts of the trunk road network, have been assessed to be of greater risk to road users in winter because of their location, altitude and alignment. The patrol vehicles are equipped to undertake pre-wetted salting should changing road and weather conditions require it.
Pre-wetted salting involves spreading dry salt and brine in the proportion of 70% dry salt to 30% of fully saturated brine with a salt concentration of around 23%. The addition of the brine to the dry salt takes place at the point of spreading and has the following main advantages:
Salt requires to go into solution before it becomes effective in preventing ice formation. The addition of the brine has the effect of reducing, if not eliminating, the time lag before the salt becomes effective after spreading.
The brine minimises the amount of dry salt removed from the carriageway by the draught from the spreading vehicles, road traffic and strong cross winds. More salt adheres therefore to the road surface after spreading and this can increase the length of time the salt lasts without retreatment.
The brine ensures that the “ bounce” of salt crystals onto the road side verges during spreading is minimised and that the greater proportion of the salt spread is contained within the carriageway. This leads to reduced corrosion on roadside structures and environmental benefits.
The changeability of the Scottish weather patterns means that even with this new and improved method of precautionary salting ice formation on roads can still occur. Motorists should be aware therefore that there will still be times when motorways and trunk roads will not remain completely free of snow and ice.
