Also, who the heck salts streets ahead of time? Maybe if you're expecting some freezing rain, but not snow. Might work on the first inch of snow but after that it gets washed away and you end up with a great ice/slush base under the new snow. You put it on top, either to melt thin sheets of ice or the fallen snow that gets compacted into ice by traffic.
Where I live, most of the time during the winter temperatures are too cold for salt (and other compounds) to be effective anyway. I don't even bother cleaning the driveway until there's 4-6 inches of snow on it.