On many British winter mornings, drivers will awake to find that the gritting lorries have been out in force overnight making the main roads of the UK as safe as is practicable for its multitude of drivers.
You may be surprised to learn that there is a lot more to effectively de-icing the nation’s public thoroughfares than simply scattering salt around all over the streets!
The efforts of De-Icing road gritters means that the countries traffic is kept moving along, as much as possible, even during the most severe winter weather conditions.
How does road gritting work?
The material that is most often used on the UK’s roads is normally rock salt these days. Rock salt is favoured because it both lowers the freezing point of any water (in whatever form) on the road surface and halts ice formation in the first place also causing any existing ice or snow to melt away too!
Getting the timing right is vital for success!
One of the most important considerations in effective gritting is timing. For example, if the first coat of rock salt was performed around 4pm, before the evening rush-hour, there may be another coating at 10pm afterwards. If winter conditions are expected to persist then there may be another coat done at 2am and then a final pre-morning rush-hour coating at 6am.
If the roads are gritted too early then the grit may be wasted because it can be blown away by wind or displaced as vehicles drive over it. The perfect conditions to grit a road with rock salt are when the road surface is already damp, as it will stick more effectively. This is preferable to waiting until a layer of ice has formed, for the same reason that gritting a dry road is often avoided where possible.
Gritting of roads during the rush-hour is a no-no too as the lorry would likely become stuck with the rest of the traffic, going nowhere fast!
The drivers of gritting lorries usually aim to spray the road as symmetrically as possible all along its width. The driver can, if desired, also alter the width of the spread and the angle of delivery, depending on the actual road conditions that he/she experiences.
How much is enough?
The amount of rock-salt that is used varies widely. The amount that it is necessary to spread depends upon the amount of frost, ice and snow present. In a light frost for instance, they may only need to use 10g of rock salt per square metre of road, in deep snow they may need to use as much as 50g, five times as much, because a more aggressive melting action is needed.
The gritters need traffic to help the rock salt do its work; this is because without traffic it will not mix readily and go into solution in the water present on the road surface. A nice brine (salt water) solution is the ultimate objective, for the best effect with maximum impact.
When do the gritters know that it is time to go to work?
In a perfect world, the gritting lorries will be sent out before the first snowfall arrives. This means of course that it is of vital importance to keep an eye on the weather forecast. When temperatures are expected to dip below freezing point for any sustained length of time, the roads will need to be gritted.
The actual air temperature is actually largely unimportant too because there can be a few degrees Centigrade difference between the road surface itself and the air above it due to wind, fog and other effects.
In the 21st century, some local councils will even have their own sensors located within their most important road surfaces, sometimes incorporating GPS to predict the actual local road surface weather conditions with pinpoint accuracy.