Now this is a wonder to behold. Because the normal road salt does not work when temperatures are below 16 degrees, transportation people have begun adding various additives which they believe keep salt working at temperatures as low as - 25.
Some states are using beet juice which contains carbohydrates that keep ice from sticking. Milwaukee (of course!) has been adding cheese brine which when added to beet juice keeps the salt from scattering and also cuts way back the amount of salt needed.
New York has begun using the cheese brine as well. Des Moines is using garlic salt and parts of Ohio have begun scattering non toxic coal ash while Washington state is using a mixture of molasses and saltwater which creates a gooey mix that keeps roads clear up to 4 days.
Anything that works, use it.