> 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

Salt isn't effective when it gets really cold so it tends to be applied more around freezing as opposed to below. It also depends on the road surface temperature as well, heat of the sun melts off snow and that freezes at night. So you'll find salt has to be applied intelligently to the conditions, on bridges for example, which I suppose would come from experience.

I also observe southern states seem to use more rubber instead of rock in their road surface. So that might be a factor on how robust they are to wear.

0F is defined as the temperature that salt on ice reaches. Regular salt is used a lot in Minnesota because it works fine most of the time and is cheap. It doesn't work on the coldest days, so about 15F they start adding in salts other than NaCl. Below -15F they no longer have a salt that works at all - but those days are rare.

My Grandpa worked for the MN highway department until around 1995 when he retied, so my information is a bit out of date, but chemistry doesn't change that much so I doubt it is very different today.