There have been studies about why these multi car pile ups happen in the fog so much.
Part of it is that when the fog is so thick your eyes are glued to the road. You don't dare take your eyes off the road long enough to look at your spedometer. Combine that with not being able to see other objects; such as trees, signs, etc; and you can't judge how fast your going. Next thing you know your speeding then BAMN there's a car in front of you that was not going quite as fast.
Actually there's an explanation for that!
Threaded Mode