In the Central NY area (Syracuse, Rochester, etc) they used rock salt - and LOTS of it - on the roads in the winters. This was back in the late 70's through the early 90's, don't know if it has changed now. I just couldn't believe how bad it was when I moved there, a 5 year old car could have holes in it. Will never forget driving down the snowy highway and watching a lump in the carpet under my feet that kept getting larger. Peeled it back and found the floor had completely rusted through. And this was maybe a 7 year old car.