Driving is a visual activity, so driving when visibility is reduced is one of the most dangerous situations you can encounter behind the wheel. And few conditions restrict visibility more than dense fog.
Fog is comprised of tiny particles of moisture suspended in the air in sufficient density to impede vision – in effect it's a cloud that forms at ground level when the temperature falls far enough for the air to become saturated and water vapour in the air condenses to form suspended water droplets.
Visibility can be even worse when it's dark as the water particles reflect the light from headlights, and street lights, creating glare.
The best advice for driving in fog is, "don't." Stay where you are if that's possible. But if you absolutely must drive, here are a few tips to help you reduce the risk.
1 - Keep your windows clear. Use the intermittent wiper setting to sweep away water as it deposits on the outside of the glass and direct enough defroster air to the inside of the windshield and side windows to prevent them from fogging.
2 - Switch your headlamps to low beam. The higher the headlamp beams are aimed, the more the fog will reflect light back in your eyes. If you have fog lights, try them to see if they improve the situation. They may not for many are more decorative than functional.
3 - Be sure you can be seen. Make sure your tail-lamps are on, even if it's not dark, and if your vehicle has a rear fog lamp, as do many European models, turn it on. If the visibility is highly restricted, turn on the four-way flashers – but only if the conditions are extreme. They can be very annoying to other drivers if used indiscreetly.
4 - Slow down. Don't drive faster than you can stop within the distance you can see ahead.
5 - Increase the distance from the vehicle ahead. There's more chance of that vehicle doing something unexpected in the fog so take extra care to provide more reaction time – and space.
6 - Use the painted lines or the edge of the road as guidelines. Use the right edge of the road as a guide, rather than the centre line, if possible.
7 - Don't rely on the tail-lights of the car ahead to lead the way. If it goes off the road you'll follow it and keeping those lights in sight might also entice you to follow it too closely for safety.
8 - Brake gently and early so your brake lights warn drivers behind. Pay attention to any sign of slippage when braking as fog may also form ice on the road surface.
9 - Be cautious for any parked or unlit cars or pedestrians that may be on the road.
10 - Don't attempt to pass other vehicles as you may not be able to see stopped or oncoming vehicles, even with their lights on.
11 - Be aware that fog conditions may not be uniform. They may get dramatically worse without warning so be prepared.
12 - Breathe and blink. Take a deep breath occasionally and the extra oxygen you take in will sharpen your vision temporarily and help you relax. Blinking keeps the surface of the eye clean and lubricated and works the muscles of the eye.
13 - Don't hesitate to pull safely off the road, stop and park, with the low-beam headlamps and four-way flashers on, if the conditions become too difficult to continue safely.