In the UK, rock salt, which is commonly used in gritting our roads, comes from three mines situated in Teesside, County Antrim and Cheshire. These mines provide up to 2M tons of salt each year and their reserves are sufficient to meet any extra demand, helping us to keep our roads ice-free.
This winter, once again, UK salt producers have met the challenge, delivering to local authorities and strategic road networks across the UK in our coldest season for several years – with temperatures as low as minus 20.0°C.
As a result of their efforts, our country has been kept up and running, and services – such as delivery and transport, continued with little inconvenience or delay.
The shorter days in winter mean we make more journeys in the dark and prolonged periods of bad weather. Rock salt helps to keep us safer in these conditions by getting rid of ice and snow. Applied in dry form, gritting with rock salt is tried and tested and supported by decades of successful de-icing results. As a non-toxic mineral, once used, rock salt can be disposed of through natural processes, making it an environmentally-friendly substance.
Gritting fleets (you’ll have seen some of the creative names given to gritters, in the media!) are run by local authorities, highways agencies and their contractors, all of whom have a legal obligation to keep our roads clear. This is a large undertaking with many local authorities responsible for thousands of miles of roads that must be gritted as soon as temperatures start to fall. In addition to the actual task of de-icing, they must ensure their salt stocks are kept at the levels set out by the Government and, working closely with the Met Office, forecast when the weather will be cold enough for the gritters to be sent out.
It will come as no surprise that de-icing our roads is a multi-million pound operation, funded from local authority council tax. The DfT estimates that the welfare cost of disruption to domestic transport is around £280m per day in England and the direct economic costs amount to £130m per day.
So how does gritting make the roads safer? Salt lowers the freezing point of water, meaning that the temperature must drop before moisture on the road surface will turn to ice. When used alone, salt is effective at preventing the freeze down to approximately minus 10.0oC but it can be combined with additives to keep it working at lower temperatures and to improve its spreading characteristics, meaning less is needed. Its large granules also provide traction for tyres on icy surfaces, reducing the risk of skidding, preventing accidents and, therefore, lessening the burden on the NHS and emergency services.
The degree to which the temperature is lowered is dependent upon the amount of salt used. Therefore, if the temperature is expected to fall significantly overnight, a greater amount of salt is needed to prevent the roads from freezing. This knowledge enables local authorities to manage the amount of rock salt that they spread on each gritting run and maintain their locally held stocks over the course of the winter.
Looking ahead, the UK’s salt producers will continue to support local authorities and strategic road networks across the UK, helping to keep our roads open throughout this wintry season and beyond.