Thursday 23 May 2024
12.7 C

Road Gritters out as road temperatures drop to -4ºC – see gritting maps

Gritters will be out across the city and county for the next few days.

Councils will be out gritting roads as winter temperatures arrive this week.

Road surface temperatures are forecast to be -1ºC tonight, and down to -4.7ºC up to the weekend.

Gritters are on part-time standby from October, then 24-hour standby from November until April.

Gritters go out when forecasts suggest:

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  • road temperatures will be at 0°C or below
  • moisture will be present to form ice.

The road temperature often stays higher than the air temperature because roads retain heat from the sun longer than the air.

Roads do not cool down nearly as quickly as objects such as cars. This means frost on a car can be a misleading guide to whether gritting is needed on the roads.

When council gritters have been out salting Nottinghamshire roads, this won’t necessarily prevent snow from settling on roads.

When they spread salt on roads it will mix with any moisture and create a saline solution (basically salty water). This has a lower freezing point than water and therefore helps stop ice form on the road, even though the temperature is below the freezing point of water.

The actual freezing point of a saline solution depends on the salinity (strength), and that relates to how much salt we put on to roads or how much residual salt is present on the roads (e.g. from previous gritting runs).

Gritters apply an amount of salt to ensure, as far as possible, that the salinity of any moisture on the roads is sufficient to prevent ice forming. We usually apply 15gms/m2 or 20gms/m2.

At temperatures below minus 6 degrees the effectiveness of the salt is reduced. Therefore there is a chance that ice could form even though they have gritted roads.

Salt will not directly melt snow. It first has to mix with the snow to form a saline solution.

They spread the salt in advance of snow so it can start to mix to create the saline solution, to help to reduce the accumulation of snow and also help to prevent ice forming.

However, in prolonged periods of snowfall, the snow can fall at a rate faster that the salt can mix with the snow. Therefore snow will accumulate no matter what they try and do in advance.

Vehicles travelling on the roads help the process by breaking down the snow and helping the formation of the saline solution.

So, when you look at a main road and see snow has settled, it does not necessarily mean that the road has not been treated. It simply means the rate of snowfall has been enough for it to accumulate while the salt is still mixing to form a solution.

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Nottingham City Gritting Map

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