Question

insert one comma to separate the coordinate adjectives. the dark foggy conditions resulted in limited road visibility, so the state troopers temporarily closed all major thoroughfares.

Explanation:

Coordinate adjectives are adjectives that describe the same noun and can be separated by a comma. In the phrase "dark foggy conditions", "dark" and "foggy" are coordinate adjectives as they both describe "conditions" and can be swapped (e.g., "foggy dark conditions" still makes sense). So a comma should be inserted between them.

Answer:

The dark, foggy conditions resulted in limited road visibility, so the state troopers temporarily closed all major thoroughfares.