Gritting Myths – Q&As!

Will road grit melt the snow?

No.

Road grit doesn’t directly melt snow as it first has to mix with the snow to form a saline solution lowering the melting point. If snow is predicted, road grit is spread in advance so when the first snow falls it can start to mix with salt to create a saline solution which can reduce the build-up (accumulation) of snow and prevent the formation of ice.

Pre-gritted roads require traffic to aid the mixing of salt and snow to ensure it is most effective. This is why when significant traffic moves on the road, it appears as grey/black slush, which effectively means the gritters have done their job, as the snow has not been able to stick to the road surface.

However, in prolonged periods of snowfall, the snow can fall at a rate faster than the road grit can mix with the snow, which means the snow may accumulate.

How does road grit prevent frost and ice from forming?

Frost and ice form when water freezes. Road Grit spread on roads and pedestrian areas mixes with any moisture and creates a saline solution. Saline solutions freeze at a lower temperature than water, so frost and ice don’t form on the road, even though the temperature is below freezing for water. It’s for the same reason why salty sea water freezes at a lower temperature than fresh water. The actual freezing point of a saline solution depends on the salinity (strength) of the saline solution.

The right amount of road grit is spread on the roads to ensure, as far as possible, that the salinity of any moisture on the roads is sufficient to prevent frost and ice formation.

At temperatures below minus 6 degrees, the effectiveness of the road grit is reduced.

When is the best time to spread road grit?

This depends on a variety of factors. As we know certainly from the weather forecast the roads will require gritting treatment, where possible we carry out the gritting treatment in the evening at approximately 7.00pm. Gritting at this time ensures the best performance of the grit. Spreading road grit at these times also means the roads are treated in advance of peak traffic flows, before the times when frost and ice will form, and when there will be enough traffic on the roads to help the salt mix with the moisture to form a saline solution.

Where the weather forecast cannot confirm with certainty that a treatment will be needed, we will continuously monitor the weather data and order a grit treatment only if it is needed. If the time of road grit spreading coincides with rush hours, the gritters can be severely delayed and get stuck in traffic, so we always try to avoid gritting during rush hours wherever possible. Difficulties can arise when rain is forecast to continue right up to the time of freezing or when the rain is forecast to turn to snow. In these circumstances, the gritters must wait until the rain has stopped or the salt will be washed away.

Stages of Gritting Road Grit when it Snows!

Pre-salting before major snow accumulation on the road surface – you can see the tyres marks of vehicles aiding the mixing process at this stage.

Pre-salted road surface has had little traffic and significant snowfall in a short period – but crucially underneath the snow, the road grit is just waiting to react to traffic and ensures the snow has not frozen to the road surface.

Pre-salted road where minimal traffic is starting to move – even during significant snowfall. You can start to see the tracks to the road surface start to appear as the salt works in tandem with the traffic.

Pre-salted road as traffic moves in greater volumes – the effectiveness of the road grit is increasing as the traffic does.

Pre-salted road in the final stages – as the optimum traffic flow occurs and the ‘slush’ of unfrozen snow and ice has not been able to form on the road surface – due to the gritters successfully completing the process – often after many an hour behind the wheel!