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.