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SALT, MOLASSES, GRITTING AND BEST PRACTICE
Page 45
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There are two techniques for applying salt to Britain's roads: pre-wet spreading and pre-mix salt spreading.
The pre-wet salt spreading system is used on motorways and dual carriageways with 6mm rock salt, which is mainly sourced from the UK's only salt mine in Winsford, but it is also imported from Chile.
Andrew Lupton says: "The pre-wet element is pre-saturated brine, which is seven parts water and three parts salt. The water, housed on the side of the hopper, is sprayed onto the salt just before distribution. Pre-wet's beauty is its ability to stick where it lands."
One of the problems with pre-wet spreading is following and passing traffic. "If drivers choose to go for a wide spread, they find that you have a lot of shadowing with other vehicles. The salt distributor might be able to throw it up to 17m, but if you have vehicles [trucks especially] shadowing the vehicle, the salt will hit the vehicles instead of the road surface," he says.
In urban areas, gritting is done with ow-throw distributors and a different salt mix. Safecote, formed of a molasses, which is a byproduct of sugar, is imported from the US, then mixed with salt to produce a dry-granule salt. This is distributed onto the road, and it bounces under parked cars, creating a wider spread pattern.
When it comes to treating roads, the local authority or contractor responsible will pay for a 24-hour weather forecast service and use thermal route imaging to monitor the temperature of their road network.
When adverse weather is identified, they have an hour to load vehicles before leaving the yard, and two hours to cover specific routes. A pre-defined winter road plan will identify which routes are priority, and authorities will look to cover up to 30% of the network.
Officially, a council's winter starts at the beginning of October and finishes at the end of April, with December, January and February being high-risk months.
Storage is a major issue for councils, says Lupton, because they have sold most of their land, including salt storage.
Recruiting drivers to grit and salt the roads can also prove problematic for authorities and contractors. The nature of the work — seasonal and inconsistent means there are issues over drivers' hours and providing training on spreading equipment.
English is frequently not the drivers' first language, and drivers may be from out of the specific local authority area, which means they have little local knowledge of routes. For Econ, damage to rolling stock is the biggest concern, and the company has 18 mobile engineers to service and repair its fleet.