Question reference: S5W-15259
- Asked by: Alexander Burnett, MSP for Aberdeenshire West, Scottish Conservative and Unionist Party
- Date lodged: 14 March 2018
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Current status: Answered by Humza Yousaf on 21 March 2018
Question
To ask the Scottish Government, in light of the practice adopted in Europe, what consideration it has given to using pure rock salt instead of a mix of grit and rocksalt during hazardous icy road conditions, which is understood to minimise issues caused by excess grit.
Answer
Our winter service includes precautionary salting of all carriageways and the more important footways in advance of forecast ice and snow. Since 2007-08, pre-wetted salting has been used on all our trunk roads.
Our pre-wetted salting involves spreading dry rock salt and brine in the proportion of 70% dry salt to 30% of fully saturated brine with a salt concentration of around 23%. All salt for de-icing on our trunk roads is required to be 6.3 millimetre grading particle size complying with British Standard 3247:1991 and treated with an anti-caking agent. Our contract specification does allow for abrasive aggregates to be considered in a ratio of 50:50 with salt but this is rarely used and is predominantly as an additional mitigation measure for extreme snow events.
Transport Scotland continues to collaborate and support winter service best practise on a local, national and world level through its current relationships with Local Authorities, Highways England, the National Winter Service Research Group (NWSRG) and the World Roads Association (WRA).
For winter salt treatments, roads authorities in Europe and North America are moving more and more to liquid-only spreading to prevent ice forming on roads. Recent studies from Europe have demonstrated the durability of liquid brine-only spreading in comparison with pre-wetted salt. They concluded that for precautionary salt treatments, especially on dry and moist surfaces, that sodium chloride brine-only spreading is recommended because it requires less salt and stays longer on the surface. For the past four winter seasons, we have been trialling sodium chloride-only liquid treatments on specific routes (A9, A77, A702 and A835) to develop our understanding of liquid performance in the range of conditions experienced on the Scottish trunk road network.