Fog can be thought of as a cloud at ground level. It forms when the temperature drops to the dew point (the temperature at which air is saturated), and invisible w
ater vapor in the air condenses to form suspended water droplets. Fog can reduce visibility to 200m or less, creating hazardous driving conditions. Driving in heavy fog is like driving with a blindfold on. Statistically it's the most dangerous driving hazard in existence. No matter how important the trip is, it's not worth gambling your life. By far the safest thing to do if you run into fog is to move well off the road and wait for the fog to lift. However, the simple and safe solution is not always the most practical. If you can't postpone your trip until dense fog lifts, follow these simple & safe driving tips during fog:
Use headlights when visibility is seriously reduced, generally when you cannot see for more than 100m, to make sure that you can be seen. Drive with headlights dipped on low beam. High beams will only be reflected back off the fog and actually impair visibility even more by creating a "white wall" effect.
There's no obligation to use fog lights, but they must be switched off when visibility improves. Familiarise yourself with your front and rear fog lights, know how to switch them on and off, and use them when appropriate. Don't keep switching them on and off, this can be a distraction to you & others. Wait for a consistent improvement in visibility before switching them off. However, if your car is involved in an accident in reduced visibility and its fog lights weren't on, then it may be queried by an insurer. If the road has street lights on, then you probably don't need fog lights on.
Do not use hazard lights, emergency flashers or blinkers while moving, these are meant to indicate a stationary hazard. Think about what other drivers see when they're behind you. If you drive with your emergency flashers on or keep tapping your brake pedal, you'll make them nervous and they may try and pass you, a procedure that places both the lives in danger.
Use windscreen wiper-washers, defrosters, defoggers, demisters, as necessary to keep your windows clear for maximum visibility.
Reduce your speed & watch your speedometer. Fog creates a visual illusion of slow motion when you may actually be speeding.
Listen for traffic you cannot see. Open your window a little, to hear better.
Use the edge of the road or painted road markings as a guide.
Be patient. Do not cross the lanes of traffic.
Do not stop on a freeway or heavily traveled road. If your car stalls or becomes disabled, turn off your vehicle's lights, turn on your flashers and take your foot off of the brake pedal so that others know you're there but won't think you are driving on the road. People tend to follow tail lights when driving in fog. Move away from the vehicle to avoid injury.
Only drive as fast as conditions allow and maintain a greater distance between you and the car in front. Change the three-second rule to four-second or more. The three-second rule: "As the rear of the vehicle in front of you passes an object at the side of the road such as a power pole, a tree or a sign, start a three-second count 'one thousand and one, one thousand and two, one thousand and three'. If your car passes the object you picked before you finish the three-second count, you are following too closely. Your crash avoidance space is not large enough. Slow down, and repeat the count again until the three-second crash avoidance space is achieved."
Tailing someone's rear lights can give a false sense of security and is dangerous.
Do not accelerate to get away from a vehicle that is too close behind you.
Check your rear view mirrors before you slow down.
Signal early when you use your brakes, don't stomp on them.