Tag Archives | driving in fog

Fog factor

Fog and mist can take you by surprise. Make sure you know how to operate your front and rear fog lights and don’t confuse these with your ‘full-beam’ setting.

Your headlights should be dipped at all times and don’t attempt to navigate using the car in front’s tail lights. Instead, follow the ‘two-second rule’ to leave sufficient space between you and the car in front.

If visibility is very limited, wind down your windows at junctions and crossroads to listen out for approaching traffic.

Be clear on fog lights

Car lights have come on in leaps and bounds, so much so that fog lights almost seem unnecessary these days. However, UK law dictates that a fog light must be included in the tail lights at the rear of every car. Front fog lights on the other hand are only fitted to certain models as an aesthetic add-on for higher spec cars. Fog lights are intended to make you more visible in fog or heavy snow when visibility is less than 100 metres (approximately the length of a football pitch), they’re not designed to light your way or help you to see further up the road. A bit of mist is not a reason to turn them on. They should only be used when your car’s main lights won’t be enough to make you visible to other road users. In the UK, street lights on 30mph roads are placed no more than 183 metres (200 yards) apart. So, a good rule of thumb for using your fog lights is whether you can see the next street light up the road from the one you’re passing. By using this rule, it’s clear that it’s only going to be in the foggiest or snowiest conditions that fog lights should be used. Once visibility improves, you must switch off your fog lights because you risk dazzling other road users. The important point here is about obscuring brake lights. As rear fog lights are brighter than standard tail lights, when you brake, drivers behind you may not be able to see your brake lights illuminate and won’t realise you’re braking. Another no-no is using fog lights when it’s wet. The extra brightness of fog lights is doubled by their reflection off a wet road surface, and the bright light can cause glare through other vehicles’ windscreens if it’s raining. In good visibility, front and rear fog lights simply create unnecessary glare to dazzle and annoy other drivers.

Mist and fog

Mist and fog are often used interchangeably as they are closely related, however, there is a key difference depending on how far you can see through them. The defining difference is visibility; if it’s less than 1,000 metres we call it ‘fog’ and if visibility is greater than 1,000 metres we call it ‘mist’. Importantly, if visibility is less than 100 metres (length of a football pitch) put on your fog lights and remember to turn them off when visibility improves.

One thing drivers forget about fog is that it coats everything with a damp, moist layer in much the same way as light rain. That includes the road surface, so take this into account when you’re at the wheel. It doesn’t help that fog blanks out your vision of the road surface ahead, so the fact that the road is wet is not always obvious. This effect is worse at night, dusk or sunset. What’s more, if it’s cold enough, the moist layer will turn to ice, making driving conditions even more hazardous. So if it’s foggy, remember the effect this can have on the road surface, and drive accordingly.

When to use fog lamps

Remember, you mustn’t use your fog lamps unless the visibility is very poor – rear fog lamps will dazzle other road users, and the effect is intensified when there is spray coming out from the rear of the car. Front fog lamps have the same effect, but for cars ahead of you.

The Highway Code says that you should only use your fog lamps when the visibility drops below 100 metres (about the length of a football pitch). A good rule of thumb is to think about whether you can see the tail lights of the car in front of you. If you can’t, and you know it isn’t that far away, you (and they) should probably be using rear fog lamps.

Fog alert

Fog is estimated statistically to be the most dangerous weather to drive in. So take note that hanging on to the car lights in front of you might seem the easiest way to cope in fog, especially at night or if you are tired, but this can be dangerous. As you can’t see very far ahead, you’ll have little or no warning if the vehicle in front stops suddenly, especially if it’s using rear fog lights which can mask the effect of brake-lights.

Remember SAS – your space and speed – watch your speed and leave extra space when it’s foggy. Tips for keeping safe include: