[Bella_Bru]

Some reports say that in heavy fog situations, the brain gets a little confused and you begin to perceive that you are moving slower than you actually are. Up in Sacramento, CHP has started running "pacers" on the freeways during heavy fog.

[WVNan]

I think Afton Mountain in Va. (I-64) holds the record for multiple car pileups in fog. It's so bad they finally embedded lights into the roadbed. No matter, I still wouldn't drive over that mountain in the fog.

[LenS]

Dateline did a report on this effect. In the fog, the brain loses it's sense of speed. The driver actually believes that he is slowing down when he drives through fog. To counter that perception, the driver speeds up, mistakenly believing that they are either slowing down or just maintaining their prior speed.