Road salt is useless if it's colder than 15°. It corrodes pavement and metal and it doesn't biodegrade. Not to mention what it does to water quality when it washes into streams, rivers and lakes.
Beet juice and cheese brine aren't bad de-icing options, but deer love them, and attracting deer to roadways isn't exactly improving safety.
And then there's potassium acetate. It has a lower freezing point, it biodegrades ... it's just so gosh-darn expensive.