But how do we know that the roads are going to freeze? Which roads will freeze first? Just how icy will the roads become?

These are just some of the questions that the Met Office tries to answer using its ‘Open Road’ system of monitoring and predicting the state of the roads across the West Country.

Twenty five years ago there was no such system in place. When weather forecasters were predicting a cold night gritters would go out and cover the regions roads in a layer of salt.

Unfortunately a cold night does not always result in icy roads so a great deal of expensive and environmentally damaging salt was wasted, to say nothing of the staff costs.

In the early 1980s it was found to be possible to measure the temperature of the roads by using sensors and computer models of the road surface were also developed.

By correctly forecasting the likely cloud, winds, air temperatures etc and entering this data into the model, the fist accurate predictions of how the temperature of the road would change through the day were produced.

Today these models are sophisticated enough to tell exactly when the roads are likely to freeze, how much ice will form and when any ice is likely to melt.

We monitor the road temperatures at more than 700 sites around the country. Data from these sensors is sent to forecasting centres around the country who use this data to produce the forecasts for our region.

The forecasts are sent to companies who are contracted to the Highways Agency, such as W.S. Atkins on the A46 near the M4, whose job it is to sent the gritters out when the roads are forecast to turn icy or when snow is expected to fall.

To stop ice forming they use pure salt (not grit) which comes from Cheshire or sometimes Northern Ireland. Spreading this on the road surface lowers the freezing point of any water on the road surface, preventing it turning into ice. Hundreds of tons of salt are used during each ‘season’.

We aim for something like 90% accuracy using this system. Its not foolproof and even when we get the forecast 100% right the weather condition can make effective salting of the roads very difficult. 20 years ago there was no such system in place. Salting was very hit and miss. Now, forecasters and highway engineers work together to ensure the roads stay OPEN.