Speed limits are a maximum, not a minimum. With limited visibility in fog or snow, it is extremely common to see cars going 10+ mph under the speed limit. The

Speed limits are a maximum, not a minimum. With limited visibility in fog or snow, it is extremely common to see cars going 10+ mph under the speed limit. The speed limit is supposed to be the maximum appropriate speed in ideal conditions. In practice almost no one treats it that way, but that's the philosophy by which it was designed. They take into account the clear area on the side of the road, sight lines, and the curve of the road itself.