then, about 30 seconds later I had to stop 
PennDOT used to use salt; they now use a liquid (magnesium?) and I think they also continue to use salt as well. Last year, they had a situation similar to yours, and a lot of people raised a lot of hell after being stranded during a storm. Fast Eddy Rendell lit a fire under PennDOT, and there are now a multitude of plows on the interstates whenever there is a HINT of snow or ice....
then, about 30 seconds later I had to stop I think I remember reading about that. Back in April of 1980 and 1984, I took my sons down to Florida. Inevitably, there were heavy snowfalls on the way down and back. It was so bad that we got off at several different exits in an attempt to find a motel to stay in, and they were all full. We had no choice but to continue driving, all the while seeing cars and tractor trailers off the road.
It's such a mountainous area, with so much open space that the winds blow the snow across the roads and visibility is zero. On our trip down to Florida in '80, we were driving on 81 South and because the roads were full of wet, heavy snow, driving was very slow. I remember trying to pass a slower vehicle in that crap, and I ended up sliding all the way across the road to the right and banging into the guard rail. Thank God there was no one behind me, and there was a guard rail and no cliff. Now that I'm retired and I don't have to schedule my vacations to suit my employer, I refuse to drive down 81 once any snow has fallen.
I think the liquid magnesium is for pre-treating the roads. We’ve been subjected to some freakish weather events in the last couple of years where the roads weren’t pre-treated & the temps got so cold, so suddenly that the de-icers weren’t effective. ‘Course the weather is always a bit freaky on I-81 between Tower City & Scanton.