GMC 1993 Safari Owner's Manual page 185

that you can see only a few feet (meters) ahead. It may come suddenly to
an otherwise clear road. And it can be a major hazard.
When you drive into a fog patch, your visibility will be reduced quickly. The
biggest dangers are striking the vehicle ahead or being struck by the one
behind. Try to "read" the fog density down the road. If the vehicle ahead
starts to become less clear or, at night, if the taillights are harder to see, the
fog is probably thickening. Slow down to give traffic behind you a chance to
slow down. Everybody then has a better chance to avoid hitting the vehicle
ahead.
A patch of dense fog may extend only for a few feet (meters) or for miles
(kilometers); you can't really tell while you're in it. You can only treat the
situation with extreme care.
One common fog condition-sometimes called mist or ground fog-can
happen in weather that seems perfect, especially at night or in the early
morning in valley and low, marshy areas. You can be suddenly enveloped in
thick, wet haze that may even coat your windshield. You can often spot these
fog patches or mist layers with your headlights. But sometimes they can be
waiting for you as you come over a hill or dip into a shallow valley. Start
your windshield wipers and washer, to help clear accumulated road dirt. Slow
down carefully.
Tips on Driving in Fog
If you get caught in fog, turn your headlights on low beam, even in daytime.
You'll see-and be seen-better. Use your fog lights if your vehicle has them.
Don't use your high beams. The light will bounce off the water droplets that
make up fog and reflect back at you.
Use your defogger. In high humidity, even a light buildup of moisture on the
inside of the glass will cut down on your already limited visibility. Run your
windshield wipers and washer occasionally. Moisture can build up on the
outside glass, and what seems to be fog may actually be moisture on the
outside of your windshield.
Treat dense fog as an emergency. Try to find a place to pull off the road. Of
course you want to respect another's property, but you might need to put
something between you and moving vehicles-space, trees, telephone poles,
a private driveway, anything that removes you from other traffic.
If visibility is near zero and you must stop but are unsure whether you are
away from the road, turn your lights on, start your hazard warning flashers,
and sound your horn at intervals or when you hear approaching traffic.
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