GMC 1993 Suburban Owner's Manual page 209

Tips on Driwhg 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 wiper 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 flasher,
and sound your horn at intervals or when you hear approaching traffic.
Pass other vehicles in fog only if you can see far enough ahead to pass
safely. Even then, be prepared to delay your pass if you suspect the fog is
worse up ahead. If other vehicles try to pass you, make it easy for them.
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