Do people really need speed limit signs to have half a brain when road conditions are crappy?
Reduced speed limit precedes the fog bank, so yes, it’s reduced injuries and fatalities considerably. It serves as a warning system, seeing the speed limit drop and if it drops a lot, you know it’s bad before you’re in the thick of it, can’t even see the lines on the road and can’t decide whether to keep moving so you won’t get hit, or stop so you won’t hit somebody.
Here is a link describing the various state DOT efforts and countermeasures dealing with highways prone to poor visibility, fog in particular.
The automated, visibility controlled variable speed limit system in use for decades on I-40 west of Asheville, NC is described in some detail including early bugs in the system as well as cost of implementation.
Many states have similar efforts.
Texas had no countermeasures in place, according to the study.