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 water vapor in the air condenses to form suspended water droplets. Fog can reduce visibility to 1/4 mile or less, creating hazardous driving conditions. If you can't postpone your trip until dense fog lifts -- usually by late morning or the afternoon -- follow these tips: 

• Drive with lights on low beam. High beams will only be reflected back off the fog and actually impair visibility even more.
• Reduce your speed -- and 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 wipers and defrosters as necessary for maximum visibility.
• Use the right edge of the road or painted road markings as a guide.
• Be patient. Do not pass lines of traffic.
• Do not stop on a freeway or heavily traveled road. If your car stalls or becomes disabled, turn your vehicle's lights off, and take your foot off of the brake pedal. People tend to follow tail lights when driving in fog. Move away from the vehicle to avoid injury.
• If your vehicle is equipped with automatic daytime headlights, you should remember that tail lights do not automatically turn on.   You should always turn your headlights on manually when driving in the fog or other limited visibility situations.