I agree 100% with Grumps on this:
It had been present for nearly twenty four hours. The time to begin driving cautiously was long past. Stopped vehicles do not “appear in the fog.” You may feel that way because you are driving too fast to see them in time.
Slow Down. The life you save may be your own.
One more thing; turn on your lights (low-beams, please). Visibility of a self-lighted object in fog is pretty close to twice that of one that is not self-lit. It doesn’t much help with absolute-zero visibility, but that’s where the slow down rule really comes in.
Let us not forget. Avoid the Herd! Stay out of the pack and your chances of avoiding such will be less.