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When should you switch your fog lights on and off?

When was the last time that you read the Highway Code? If you are anything like me then it is likely to have been when you were taking your driving test, or if you are younger than me, when you were taking your theory test! That for me was, *cough, cough*, over 30 years ago!

It's the end of November and here in Sawtry, and the surrounding area of Huntingdonshire and Cambridgeshire, we have woken up to fog a couple of times this month. Having driven on rural roads and on both the A1 and A14, in fog, and seeing some drivers with NO lights on at all, or day-running lights, and some blinding us with their fog lights I thought that it would be good to re-look at the Highway Code and to share that as part of our Prime Vehicle Sales blog.

When should you switch your fog lights on and off?

In the Highway Code, Rules 234 to 236 are all about driving in fog;

  • Rule 234: Before entering fog check your mirrors and then slow down. If the word 'Fog' is shown on a roadside signal but the road is clear, be prepared for a bank of fog or drifting patchy fog ahead. Even if it seems to be clearing, you can suddenly find yourself in thick fog.
  • Rule 235: When driving in fog you should
    • use your lights as required (see Rule 226)
    • keep a safe distance behind the vehicle in front. Rear lights can give a false sense of security
    • be able to pull up well within the distance you can see clearly. This is particularly important on motorways and dual carriageways, as vehicles are traveling faster
    • use your windscreen wipers and demisters
    • beware of other drivers not using headlights
    • not accelerate to get away from a vehicle which is too close behind you
    • check your mirrors before you slow down. Then use your brakes so that your brake lights warn drivers behind you that you are slowing down
    • stop in the correct position at a junction with limited visibility and listen for traffic. When you are sure it is safe to emerge, do so positively and do not hesitate in a position that puts you directly in the path of approaching vehicles.
  • Rule 236: You MUST NOT use front or rear fog lights unless visibility is seriously reduced (See Rule 226) as they dazzle other road users and can obscure your brake lights. You MUST switch them off when visibility improves.

Rule 226 is mentioned a couple of times within these rules, so Rule 226 says;

  • You MUST use headlights when visibility is seriously reduced, generally when you cannot see more than 100 metres (328 feet). You may also use front and rear fog lights but you MUST switch them off when visibility improves.
How do you judge distance?

So how far is 100 metres or 328 feet? If I were to say that your average lorry is 50 to 65 feet long then the distance in which you should NOT have your fog lights on is approximately 5 lorry lengths. Quite far! Likewise, if you cannot see as far ahead as a lorry length then you should have your fog lights on!

Having driven on rural, fen roads in fog, the visibility has been down to no more than 8 metres (25 to 30 feet), at times. Once back on major roads then the visibility has improved to at least 100 metres (328 feet). The fog lights were then turned off but the headlights were kept on.

So, if you are driving locally, please think about what lights you should be using when there is fog about.