While this is quite bad, I find what is worse, is snow partially compacted by a few cyclists so the surface becomes extremely bumpy and grooved, then it freezes. It is virtually impossible to make it over patches like that unscathed.
Originally posted by mgagnonlv
Actually, I find that one not terribly efficient, but the hardest is when the same 3-6" of snow has been compacted by cars at a decent temperature, and then froze over. It leaves an uneven 0.5 - 1" of white ice which is a "good" surface for sliding around. Hard to stay upright on such stuff... even with studded tires.