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| How do they know when to grit roads? | How do they know when to grit roads? |
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| WHO, WHAT, WHY? The Magazine answers... When snow is forecast, local councils send out the gritters. Trouble spots are identified by networks of sensors embedded in the asphalt. How does this early warning system work? | WHO, WHAT, WHY? The Magazine answers... When snow is forecast, local councils send out the gritters. Trouble spots are identified by networks of sensors embedded in the asphalt. How does this early warning system work? |
| On roads and highways across the UK, discs are embedded in the road surface to measure climatic conditions. Each is connected by cable or mobile phone technology to an automatic weather station, an unassuming grey box by the roadside. | On roads and highways across the UK, discs are embedded in the road surface to measure climatic conditions. Each is connected by cable or mobile phone technology to an automatic weather station, an unassuming grey box by the roadside. |
| THE ANSWER Sensors measure road and air temps, rain, dew and salt levelsGPS is now being used to provide detailed ice predictionsAuthorities use data to decide when to send out gritters class="" href="/1/hi/uk/7169438.stm">Freezing weather hits UK It's a system developed in the 1970 and 80s and now widely used across the country to track and predict road conditions throughout inclement months. To have accurate information about driving conditions is invaluable to road authorities and local councils to decide when - and where - to send out the gritters. | |
| The sensors are sited either on a representative stretch of road (no nearby trees, buildings or bridges, which offer some protection from the cold), or traditional cold spots. The weather stations then beam back data about air and road temperatures, wind speed and direction, and the wetness of roads. | |
| This is posted on an intranet for officials to monitor, along with analysis by meteorologists using local weather forecasts. | This is posted on an intranet for officials to monitor, along with analysis by meteorologists using local weather forecasts. |
| Salt levels are also measured to ensure that grit already spread has not been blown away by wind or washed away by rain, says David Sparks, of the Local Government Association. | |
| Sensors link to this automatic weather centre (grey box on right)"What we don't want is a worst-case scenario such as we had in the Midlands a few years ago. Cold weather was forecast and the gritters went out. But then the weather changed. The snow turned to rain, which washed away the grit, then the temperatures suddenly dropped again and the rain froze on the roads. | |
| "If you have a sensor measuring wind temperature, you'd know to send the gritters out again if it drops cold again." | "If you have a sensor measuring wind temperature, you'd know to send the gritters out again if it drops cold again." |
| Cold spots | Cold spots |
| With the UK's changeable weather, where sudden cold snaps can follow balmier days and vice versa, councils have gritters on standby from October to early April. | With the UK's changeable weather, where sudden cold snaps can follow balmier days and vice versa, councils have gritters on standby from October to early April. |
| WHO, WHAT, WHY? A regular part of the BBC News Magazine, Who, What, Why? aims to answer some of the questions behind the headlines At Dudley Metropolitan Borough Council in the heart of the Black Country, the council is responsible for keeping the roads clear in the city and the surrounding hilly district. | WHO, WHAT, WHY? A regular part of the BBC News Magazine, Who, What, Why? aims to answer some of the questions behind the headlines At Dudley Metropolitan Borough Council in the heart of the Black Country, the council is responsible for keeping the roads clear in the city and the surrounding hilly district. |
| Its sensors are placed on the outskirts of the urban area and at traditional cold spots, and are linked to four weather stations throughout the borough. | Its sensors are placed on the outskirts of the urban area and at traditional cold spots, and are linked to four weather stations throughout the borough. |
| "At times like this when the weather may change quite quickly, we're looking out for it 24 hours a day, and exchanging information with other authorities in the Midlands," says John Millar, the director of the urban environment. | "At times like this when the weather may change quite quickly, we're looking out for it 24 hours a day, and exchanging information with other authorities in the Midlands," says John Millar, the director of the urban environment. |
| Gritters load up as forecasters predict snow and chillsThe council has been using the sensors - which are constantly getting more sophisticated - for about eight years. | Gritters load up as forecasters predict snow and chillsThe council has been using the sensors - which are constantly getting more sophisticated - for about eight years. |
| And new systems that use GPS technology are available, such as one developed at the University of Birmingham and used by the Highways Agency in the north of England and local councils such as East Sussex, Falkirk and Stirling. This system combines geographical data from satellites with weather forecasts to provide far more detailed ice predictions. | And new systems that use GPS technology are available, such as one developed at the University of Birmingham and used by the Highways Agency in the north of England and local councils such as East Sussex, Falkirk and Stirling. This system combines geographical data from satellites with weather forecasts to provide far more detailed ice predictions. |
| "It doesn't do away with sensors entirely as it's sensible to have eyes on the road to complement the forecasts in case of any hiccups," says Steve White of WSI, the company which bought the system from the university. | "It doesn't do away with sensors entirely as it's sensible to have eyes on the road to complement the forecasts in case of any hiccups," says Steve White of WSI, the company which bought the system from the university. |
| Add your comments on this story, using the form below. | Add your comments on this story, using the form below. |
| Why not make this information available to motorists? Imagine your satnav being able to warn you about icy roads on your journey. Even better to plot a less risky route or warn you to take care.Mark, Nottingham | Why not make this information available to motorists? Imagine your satnav being able to warn you about icy roads on your journey. Even better to plot a less risky route or warn you to take care.Mark, Nottingham |
| These vital services are really appreciated, but they would be even better if the gritting on the pavements was more widespread, as it is often difficult to walk around in icy conditions, especially when walking down hills.Karl Chads, London, UK | These vital services are really appreciated, but they would be even better if the gritting on the pavements was more widespread, as it is often difficult to walk around in icy conditions, especially when walking down hills.Karl Chads, London, UK |
| I totally disagree with gritting the roads, Half the time the councils put it down when the roads are dry and there is no chance of rain, this then draws moisture out the ground and causes black ice, even if this doesn't happen, the salt generally makes the roads slippy and far more dangerous than a slight frost in the early morning. Also the corrosion it causes to cars and the road surface. If they are going to put it down then they should be made to clean up afterwards. I had a serious car crash a few years ago where a gritter had reached the county border and dumped a load of grit on a bend as he'd turned round to go back on his route. David Tidy, Horley, Surrey | I totally disagree with gritting the roads, Half the time the councils put it down when the roads are dry and there is no chance of rain, this then draws moisture out the ground and causes black ice, even if this doesn't happen, the salt generally makes the roads slippy and far more dangerous than a slight frost in the early morning. Also the corrosion it causes to cars and the road surface. If they are going to put it down then they should be made to clean up afterwards. I had a serious car crash a few years ago where a gritter had reached the county border and dumped a load of grit on a bend as he'd turned round to go back on his route. David Tidy, Horley, Surrey |