Winter maintenance

gritter loading

When gritting starts?

We start watching the weather from October each year and continue 24 hours a day, 7 days a week until the last frosts of spring.

At 1pm each day, the Met Office weather centre at Manchester sends a forecast to the Town Hall in Blackburn. At weekends and on bank holidays a duty officer gets the forecast. Based on the forecast, we decide whether or not to send the gritters out to spread salt.

The forecast includes a graph, which shows predicted road surface temperatures each hour for the next 24 hours and a description of the weather expected over that period.

Sensors embedded in the road surface constantly monitor weather and the road conditions. They transmit that information together with an indication of the amount of salt on the road surface to the Council every hour. We can also use similar information from road sensors at various locations throughout Lancashire.

We use that information to check if conditions are getting worse or better, so we can react to changes in the weather. This monitoring continues night and day.

If the weather forecast changes significantly from the one we get at 1pm, the Manchester weather centre will send an updated forecast.

Salt spreading

Ice starts to form and snow starts to settle when the surface temperature of the road drops below zero.

When salt is spread it has the effect of lowering the freezing point of any water, thus helping to prevent the road from becoming icy.

Salt must be spread onto the road surface before the road becomes icy or snow starts to fall. This is known as precautionary salting.

It takes the gritters around four hours to spread salt on the main gritting routes. So we aim for the gritters to set off at least four hours before sub zero or snowy weather is forecast to arrive.

It's a bit more difficult when rain is forecast to continue right up to the time of freezing or rain is forecast to turn to snow. The gritters must wait until the rain has stopped or the salt will be washed away and therefore have no effect.

So in that sort of weather it may not be possible to spread salt on all of the roads included in the gritting routes before the rain freezes or the snow starts to settle.

If the time of salt spreading coincides with peak traffic periods, such as going to work or returning home times, the gritters may become delayed in traffic and can get stuck along with the cars, buses and lorries they are trying to help.

When snow is forecast salt is spread on the roads to slow the rate of snow settling. Much more salt is needed than when spreading salt to prevent ice forming. Salt alone has very little effect on snow. Once snow has started to build up on the roads there is little anyone can do until it becomes deep enough to plough (about 25mm or 1 inch). The actions of ploughing, spreading salt and vehicles running on the snow will all help to clear the roads.

During times when temperatures remain below zero for an extended period or when there is heavy snowfall, we give priority to the roads on the main gritting routes. Once these are safe and clear of hazards, we turn our attention to other roads. That usually begins with through routes in housing estates and built up areas and continue with less busy side roads.


There are four principal and four non-principal gritting routes within the borough. The principal routes include all of the main roads and the non-principal routes most other busy roads.

Roads with hospitals, fire stations and police stations are included on the gritting routes along with main bus routes. These eight routes are called main routes and are always salted when any wintry hazards are forecast.

As well as to the eight main routes there are three high level gritting routes. These routes include all of the main roads (mainly rural roads) 500 feet or more above sea level. They are salted when wintry hazards are forecast to affect only those roads that are high up.

Salt bins

For roads not included on the main gritting routes, salt bins may be provided. It's just not practical to put a salt bin on every such road, so we use an assessment system to determine priorities. The system takes account of things like how steep the road is (gradient), junction hazards, drainage problems and the number of pedestrians.

Salt from salt bins is meant for use on the roads and not on private paths and drives.

Road users

There is clearly a responsibility on every one of us to drive with care, especially during winter weather. Salt spreading does not make roads completely safe, so even if the gritters have been round, take care.

The Met Office issues regular forecasts and each night on TV and radio, warnings may be given of likely adverse road conditions.

Pay attention to any warnings and set your alarm earlier to allow more time for your journey.

If weather is really severe think about whether your journeys is really necessary.

Watch out for tell tale signs, like frost on the car and icy puddles. They mean that the roads may be slippery. You may be travelling on a road that is not part of a main gritting route or you may be on a road before it has been treated. If this is the case, slow down.

Icy or snowy roads are usually passable if motorists are careful and drive sensibly.

Facts and figures

The Council has 8 gritters to which snow ploughs can be attached if required. We also have a snow blower. The gritters and snow blower are operated by the environment department.

80% of all salt spreading operations take place between 6pm and 8pm and between 5am and 7am.

Salt is spread at 10 grams per square metre for a frost warning.

Salt can be spread at up to 40 grams per square metre for a snow warning.

Salt lowers the freezing point of water and is not very effective on top of ice or snow.

Approximately 2000 tonnes of salt are spread on the borough's roads during the average winter.

There are 340 miles of roads within the borough of Blackburn with Darwen of which around 165 miles are included on main gritting routes.

Each winter season the Council provides, maintains and removes around 350 salt bins at various locations throughout the borough.

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