Following the first really cold night this autumn, the salt gritters have been our in force. We explore why salt is the ideal method of deicing in terms of efficiency, cost savings, safety and protecting natural resources and the environment.
Keeping The Traffic Moving
Over two million tonnes of rock salt is spread onto our roads each year at an average cost of £150 million. Most of it is spread onto main roads, trunk roads and motorways; without it traffic delays would cost the country a staggering £280 million each day.
In 2001, people trying to travel just before Christmas were left stranded on major Essex roads, including the M11, when a severe freeze struck before roads had been salted. It made national headlines at the time and people were literally parked on a major motorway as conditions made driving impossible for a prolonged spell.
Worth Its Salt
It’s clear salt is the single most significant method to keep roads clear of freezing, and reducing costly delays and accidents. It’s not the same as gritting roads – in fact, the term ‘gritting’ is something of a misnomer as it’s almost certainly salt that is spread onto the roads now. The brownish colour, which may make it look like grit, is actually marl, which is used in small amounts in the salt.
Gritting – when a combination of sand and small stones was spread on the roads – fell out of favour due to claims being made by motorists for windscreen damage, and the use of salt has become a precise science.
How Salt De-ices The Roads
Despite its granular appearance, salt doesn’t act as a physical tyre grip enhancer. It works by lowering the freezing point of water – and only becomes effective when it turns into a liquid-like brine which happens as it gets crushed by traffic.
It’s not just a case of throwing salt liberally all over the road when temperatures drop. The amount of salt to be used is carefully managed; salt spreader vehicles have calibrated metering and the flow rates and bulk density of salt are carefully measured.
Knowing When To Add Salt
It’s not just a decision based on the local forecast but is far more precise than that. Many larger roads have sensors positioned at certain points and connected to an automatic weather station. They beam back data, which is then analysed by local authority officials and meteorologists. GPS is also used to provide detailed ice predictions.
Levels of salt already spread onto the roads are monitored, too. Decisions on whether to re-salt roads have to be made if, for example, rainfall washes it away.
It’s important to get it right of course; local authorities are responsible for controlling the de-icing of roads within its boundaries, and it’s a balance between the costs of road salting and keeping roads clear and safe.
Where Does The Salt Come From?
It’s mined – literally from ‘salt mines’ in Cheshire, Teeside and County Antrim in Northern Ireland. As seawater evaporated following a time when the UK and Ireland was covered by inland seas, vast salt deposits were left behind that were eventually covered over. Once mined, the salt has an anti-caking agent added before being stored ready for onward transportation to gritting depots around the country.
The trade body for salt producers, The Salt Association, estimates the UK’s salt mines have some 140 miles of tunnels which make them nearly as long as the M5 motorway.
Is Salting Roads Environmentally Safe?
As a natural substance, salt is perfectly safe to use and isn’t classed as a hazardous substance. As the amounts of salt used are carefully regulated according to usage demands as discussed above, it’s not likely that excessive amounts are being washed into water courses.
Salt is the sixth most abundant element on earth, and the mining of it causes no subsidence or other risk to land or cause waste, and its highly soluble nature means any that does run off a road surface will soon return to the sea from where it originated. It’s fair to say road salt is a truly biodegradable resource.
It’s therefore a safe method for other applications, such as businesses spreading it in their yards to make them safer, or householders de-icing driveways and garden paths.
Newer road design and more recent road revision projects incorporate features that keep the salt from running off indiscriminately with water when the ice melts.
The Environmental Agency is instrumental in providing guidance for salt storage and guidelines for careful monitoring of when and how much salt to use.
Where To Get It?
You may be familiar with the salt & grit boxes on the streets, but these are only for public paths and roads – you really should not be using it on your drives. If you wish to protect your own property or business from ice, you can order salt from a local supplier, such as Milestone Supplies, who deliver their salt all over Essex.
A Natural Solution
It’s clear that salt is a natural and abundant road de-icer. With the high degrees of precision possible in terms of how much and how often it should be used to keep roads ice free, thus reducing waste and excess use, it’s a very efficient method of keeping traffic moving safely on our roads.