Not sure where -7 comes from - the eutectic point for sodium chloride & water is -18C = 0F
I agree with Brian, it is still effective at -10C or so. But when it comes into -20's (it rarely does here) salt becomes ineffective for sure, and the roads become a real icy horror.
The real fun will come when the top surface of the ice melts ...
Not so cold at the moment in Poltava, but the roads are involved into continuos cycle: melting - freezing - polishing - melting etc. Conditions are just perfect for it: +3C daytime, -3C at night. I can post an image of this horror tomorrow if anybody wants.
...But you don't know the most interesting fact about it! I'm learning to drive and having my first practice at the city streets at the moment! Funny, isn't it?
