When I was a pharmaceutical salesman, the location of that catastrophic wreck was near my territory. This mountain is a pretty good sized mountain (for the Smokies) and there are multiple run-away truck ramps headed toward North Carolina after coming down from the gap.
My wife is afraid of heights and I am a little stupid... okay, a lot stupid... and I hauled ass down that mountain in our van in an effort to feed her anxiety. Christine dug fingernail holes in her armrests. In my defense, I drove over 30 counties and I covered them every 6 weeks, so I have experience driving in areas like this.
In fog, coming down that mountain, I can imagine that it is insanely dangerous!