Question

If fog or smoke becomes so thick that you cannot see well enough to keep driving, __________

Answer 1

I believe the answer is: pull all the way off the pavement and stop then, turn on your emergency flashers.

Emergency flasher could be turned on by passing the hazard light button. The purpose of this emergency flasher is to make sure the other drivers are aware of your location in the thick smoke so unwanted accidents/collisions can be avoided.