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.

> ... because salt is mostly usable for light to moderate snowfall and ...

Perhaps more important - salt's effectiveness fades as the temperature decreases. Sand and gravel do not have that problem. So if you're running the Road Dept. in an area where serious cold ain't some rare event - why would you bother with salt?

EDIT: I know the "melt to pavement, solar heating finishes the job" tactic. Which can work with heavier snowfall, if you plow/shovel before salting. Colder weather inhibits both halves of the melt-&-heat. (Plus the further north you are, the shorter & slantier the sun's rays get, even on clear days.)

Because the goal is to get the road surface exposed so it'll heat up and melt off the snow during the day. And then the residual salt will leave a residue which will help prevent refreezing.

That only works in places with relatively milder winter climates. In harsher climates, salt stops melting snow, and the surface temperature of even exposed road may stay below freezing even during the day.