I've been riding my bike every weekend throughout the Winter (weather permitting). Weather permitting means unless it's raining or snowing or below 32F- I'm riding. In addition to the salt on the road there is an over-abundance of gravel. I'm sure there is some glass mixed in with that gravel too. Just like your car should have all-season tires in the Winter (as a minimum), so should your bike. I ride with Continental Grand Prix 4-Season tires and I love them. They're constructed with Duraskin and a double Vectran puncture-resistant belt and reinforced sidewalls that stand up to brutal conditions. They're also made with a rubber composition that performs well in cold temperature. It's a great Winter/early-Spring tire. I take them off when I ride in the Summer/Fall.
It's also a great tire for riding dirt/gravel roads like the Hell of Hunterdon bike ride in March (in my area). In the Spring/Summer, I swap the Continental 4 Season tires for the Continental Grand Prix 4000 II tires. They're not as stiff, they're lighter and they have great wet weather traction. They're made in Germany where they know a little bit about automotive products (BMW, Mercedes Benz, Porsche, Audio automobiles not to mention Michelin and Continental tires).
Power ON! Coach Rob