Fog

While fog occurs most frequently during the winter, it should be treated as a hazard which can be encountered at any time of year. The weather can be misty even in summer, and sea fog is always a possibility on a coastal road. The simple answer to the problem of driving in fog is don't, but there will always be occasions, for example if a journey is essential or you are caught on the road, when you have to drive on. However, if fog is really dense, bear in mind that an unscheduled stop in a hotel is infinitely preferable to a spell in hospital.

The basic rule for driving in fog is that you must reduce your speed so that you can stop within the range of your vision, even if this means a speed of only 5mph. Of course, such a low speed would probably make it pointless to persevere with your journey. You are asking for trouble if you attempt to drive faster than 'braking distance rate'; before long you will collide with something or someone.

Some drivers are tempted to pick up a white line and follow it blindly. You may be lucky and get away with this technique for years, but eventually you will crash into the back of a stationary, unlit vehicle. White lines and cats eyes should be used only as a guide to where the road goes, so rely instead on your own eyesight. Never straddle a centre white line - you might meet someone coming the other way doing exactly the same thing.

Always be prepared to find somewhere safe to stop and wait for the fog to lift if it is very dense. Do not park where another vehicle might run into the back of you, and leave your sidelights and hazard warning lights switched on.

Always keep your car's headlights on dipped beam in fog whether it is day or night; never drive on sidelights alone. It is absolutely vital in fog that other drivers should have maximum warning of your approach, so the dipped headlight rule exists in order that your vehicle is seen, not necessarily for you to see. It is better to avoid using main beam, because fog reflects so much light that dipped beam generally gives you a better view. Fog lamps, if you have them, are designed to give better light penetration in fog.

Junctions are particularly hazardous in fog, so a safe rule is to flash your lights and sound your horn when you have to cross the path of other vehicles which may be hidden in the fog; it is best to wind down your window so that you can listen too. Exercise special care when turning right, as an approaching driver will not be expecting a car to emerge from the fog in front of him.

If rear fog lamps are fitted to your car, use them when visibility is less than 100 metres but take care to switch them off when the weather improves. Many motorists forget to do this, sometimes motoring round for days dazzling all the drivers who are unfortunate enough to have to follow them.

It is very easy to gain the impression in fog that a vehicle ahead of you is moving unnecessarily slowly; remember that while you can see a pair of red beacons through the fog, the driver ahead may be able to see virtually nothing. Never be tempted to overtake, since this invites a head-on collision with an oncoming vehicle. You can also be misled about visibility if you are following another vehicle, since its motion makes a slight 'hole' in the droplets of water vapour which form fog. You may feel that the fog has eased slightly while you are in another vehicle's wake, only to find, when you are committed to an overtaking manoeuvre, that it is as thick as ever.

While it is wise to stay in line, do not be tempted to stay in touch with the tail lights of a driver whose speed seems too fast for safety. In the sense of loneliness which accompanies fog it can be reassuring to drive in the presence of another vehicle, but do so only in a manner which is safe in the conditions. When you are following another vehicle, leave enough space to stop, remembering that the driver may not slow down and stop in the normal way. There is always the risk that the leader of a convoy will hit a crashed car and stop instantaneously. The result of nose-to-tail motoring can be catastrophic when a pile-up occurs, particularly on a motorway, but many people persist in driving too close and too fast despite constant pleas from the police and road safety bodies.

Publicity centres on motorway accidents in fog because they are so serious, but there is no reason why motorways should not be safer than other roads in fog, just as they are in normal weather conditions. Accidents would rarely occur if all drivers followed the rules outlined here instead of rushing blindly into the fog at high speed. You must look after yourself by driving safely and attentively if you find yourself being passed by these fools, and hope that a few may learn from your example. Illuminated motorway warning signals always post a temporary maximum speed when it is foggy, but follow your own judgement if you feel that the speed indicated is still too fast.

The dangers of fog can be reduced, although never eliminated, if you know what to expect. Listen to weather forecasts and traffic news on your car radio so that you are fully informed, and use your own experience to gauge how the weather is likely to develop during the course of your journey. Always remember that mist can occur in patches, sometimes when you least expect it. Pockets of fog can linger in valleys on an undulating country road, even in summer if the humidity, temperature and air currents are right; alternatively, high ground can be foggy on a very overcast day. Fog tends to form first over water; if you see mist developing, expect thicker patches where your road crosses a river.

You can imagine the danger if you are travelling at 60mph or so when you hit a patch of thick fog, so be prepared for it if you see any signs of mist over the surrounding landscape. Take all the usual precautions when mist does appear: drop your speed, switch on dipped headlights (and auxiliary fog lamps if you have them), and operate the windscreen wipers and washers frequently. Fog usually coats the windscreen with a thin film of moisture which gradually — and sometimes imperceptibly — reduces your visibility. Set the ventilation in the demist position to keep the windscreen clear, open the windows a little if it helps to reduce condensation inside the car, and switch on the heated rear window.