Buick RIVIERA 1993 Manual page 170

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. T r y 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, tu_m 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.