While I know to drive more cautiously, after 30 years of driving in Wisconsin, I think nothing of driving in 3-6 inchs (about 7.5-15cm) of unplowed snow on the roads. At least at speeds below 30mph (or so). Highway speeds and snow/ice just don't mix very well.

It always cracks me up when I hear of cities below the "snow belt" becoming **88** because they got one inch of snow.

But I spent Basic Army Training in South Carolina one winter and was impressed at the ice storm we got once. Imagine rain falling on tree limbs, power lines and roads, then freezing on contact. You can get a pretty thick (and heavy) layer of clear ice under the right (..er, wrong) conditions.
