How good are American roads?

> Interestingly, I expected cold places to have lower road quality in general due to things like freeze-thaw cycles and the impact of road salting, but there doesn’t seem to be much correlation. Plenty of cold places (North Dakota, Wyoming, Minnesota) have good-quality roads

Not sure about those states in particular, but I have anecdotally noticed that some of the places with the harshest winters do some of the least road salting -- because salt is mostly usable for light to moderate snowfall and the people who live in the harshest climates are often better equipped to drive on hard packed snow.

Also depends on where you're looking. Cities will have worse roads because they're always digging working on gas and water lines, some of which leak. That disturbance of the ground will make things a lot worse than some rural road where the ground hasn't been disturbed since it was created.