Buick 1993 LeSabre Owner's Manual page 176

Fog can occur with high humidity or heavy frost. It can
be so mild that you can see through it for several
hundred feet (meters). Or it might be so thick 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.
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