If you can avoid driving in the fog, postpone your trip until the fog clears enough that you can see cars in front of you. However, if your trip cannot wait, drive slowly, and put your headlights on low beams. You don't want to use high beams, because the light from the high beams will cast back, and cause glare.
Put more distance between you and the car in front of you, and be prepared to stop if necessary. Don't pass another car unless there is no way to avoid doing so. Try to listen for the sounds of traffic that you are unable to see, and if necessary, use your wipers and defroster to help you see better.
If thick fog obstructs your vision, and you can barely see, pull completely off to the side of the road. Your lights should be turned off, and your foot off the brake pedal, so other drivers won't see your taillights and think your car is still moving.
"Pavement on the roads can be the most slippery when rain or snow first starts, because accumulated dust and oil haven't been washed away," according to the Department of Motor Vehicles. When you first notice rain or snow on the road, slow down, and make sure you turn on your defroster, headlights, and windshield wipers.
If you're in a heavy downpour or snowstorm, your visibility may not be more than 100 feet in front of you, and you shouldn't drive any faster than 30 mph. It may be necessary to stop occasionally to wipe mud or snow off your taillights, windshield, and headlights.
Winter traveling supplies should include an ice scraper and brush. You should also carry chains that fit your tires, and know how to put them on. You can practice at home, so you can put the chains on easily when you need them.
Carry a portable weather radio in your car, to keep informed about weather conditions and alerts.
