If you can't see, SLOW DOWN.

[Captain Trips]

Hmmm....passing in fog....not good.

My mother's parent's died a week after my parent's wedding. They tried passing a truck on a 2-lane mountain road in the fog. I never knew them.

I once totaled my car due to fog. The road jogged about 5 feet to the right, and there was a 15 inch island right in front of me, with no room to stop.

I still get anxiety driving in heavy fog. Love the thin stuff, where you can still see about 1/4 mile, and love walking in the pea-soup. But not driving in it.

[LoTech]

I just posted this to the invisible van thread, but ..
I read somewhere that fog causes drivers to consistently underestimate their own speed, because the brain mechanism responsible for estimating speed relies heavily on black-and-white vision. Fog lowers perceived contrast, and thus lowers perceived speed.
I may have to track that article down now.