The picture in this article says it all, pretty much. The motorist, an 'elderly lady' had not bothered to clear any snow from her vehicle, except for a postage-stamp-sized hole cleared by her windscreen wipers before they gave up the unequal struggle. If this doesn't constitute dangerous driving, I don't know what does. I don't care how old she is, if you drive a car you have a duty of care, and if you don't have the wherewithall to exercise that duty, you shouldn't be on the road.
But this is just an extreme example of what you'll see on any frosty morning. Some motorists are just in too much of a hurry to get on with their important journeys to spend a minute clearing their car windows of ice. I'm sure as a cyclist I am not alone in having had near misses with drivers who haven't got a clue what's going on around them because they can't see. If there is something wrong with your eyes, you are not allowed to drive. So why do the police not take action against motorists who, through a concious act of negligence, cannot see where they are going?