Driving and Weather

Drivers are always at the mercy of the weather. Many accidents are caused by human error and dangerous driving. However, a large number of road injuries and deaths are caused by fog, snow, icy roads, strong and gusty winds and heavy rain.

Fog pockets can cause motorway pile-ups and take many drivers unaware as the rest of the road can have clear skies. Radiation fog occurs on calm clear nights where the Earth, which radiates heat at night, will lose heat rapidly, cooling the layer of air just above the ground.

Temperatures fall to the dew point and water condenses into fog droplets and dew. Cool air sinks and on windless nights the cold air will flow gently down hillslopes. The air tends to accumulate in the bottom of valleys often known as "frost hollows".

We say it is foggy where visibility is below 1,000 metres (1,100 yards) although at this distance it mainly affects aircraft. Thick fog at 50-200 metres (55-220 yards) is dangerous for road traffic and dense fog - where it is below 50m (55 yards) - seriously disrupts all forms of transport.

Wind can also be a problem, particularly for high-sided trucks and caravans. They can be blown over if gusts of wind from the side are strong enough. Open stretches of motorway and bridges suffer the worst from this, and some bridges have to be closed when there are particularly fierce cross winds..

Drivers should always regularly check the tread of their tyres, whatever the conditions. In icy problems, even good tyres are not enough, and grit or salt can be spread on road surfaces to counteract this.

Grit helps tyres to grip and salt lowers the freezing point of water and prevents ice formation. This is an expensive solution through and not wholly effective. If it rains then salt can be washed away, and even if the roads are treated in anticipation of ice forming, the ice may not form because of changing conditions over night. Because of this, forecasters often provide councils and road safety departments with site specific forecasts, allowing salt or grit spreading only where ice formation is most likely.

Across the world, weather forecasts are followed closely by regular motorists and transport managers as companies face additional costs whenever busy routes are closed. It is vital for commercial transport to be able to plan routes or reschedule journeys to make the most of good weather and safe road conditions.