Fog Lights

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You must use dipped headlights when visibility is generally reduced.

You MUST use fog lights when visibility is reduced to 100 metres or less. Rear fog lights are high intensity red, and can be seen for further through the murk. However, they can dazzle drivers behind when visibility improves, so you must switch them off accordingly.

Your fog lights are fitted to the car to make it easier for other people to see you, not necessarily to make it easier for you to see other people. For example, if you are stationary on the motorway, in a traffic jam, you need the people behind you to see you early enough so that they can begin to brake in good time.

The red and blue markers on the motorway are 100 meters apart. 100 meters is also approximately 25 car lengths. Use fog lights if you can't see the next marker post.


fog lights
The rear fog light is bright, and can dazzle in normal conditions.

Driving in Fog

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Fog can be dangerous for various reasons. As always, “YOU MUST BE ABLE TO STOP WITHIN THE DISTANCE YOU CAN SEE TO BE SAFE”.

Most collisions in fog are due to drivers not following this very simple advice.

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The four-second rule

Only a fool breaks the two second rule! Under normal dry conditions you should keep at least a two second gap between your vehicle and the one in front. When the road is wet you should keep at least four seconds of empty road between you and the vehicle in front, double the normal minimum gap.

When the car in front passes a landmark, for example a lamp post, begin counting. If you pass the lamp post before you get to two (or four in the wet) then you're probably too close, and should drop back.

In fog, as with blind summits, you should work on the assumption that there is a problem just out of sight, and be prepared to stop in the distance you can see to be safe.

Tailgaiting

If you are being tailgated (if someone is driving too close behind) then you may find it safer to gradually and carefully create an even larger space between yourself and the vehicle in front.

This will mean that you will not be required to brake heavily, and therefore the person behind will be less likely to collide with you.

The driver behind may choose to overtake, which is better for you, as then they are in front and you can choose to create another big gap. This style of driving is known as defensive driving.