Of all the skills demanded by contemporary civilization, the one of driving an automobile is certainly the most important to the individual, in the sense at least that a defect in it is the greatest threat to his life. Speed may be increased up to the point where the zone nears the size of the field, and when this happens driving begins to feel “dangerous.” Expressions of the foregoing principle may be found in such common-sense rules as never driving so fast that one cannot stop within the “assured clear course,” and never “overdriving” one’s brakes or one’s headlights. The feeling of driving on an icy surface is similar to the feeling of walking on ice despite the different cues and different muscular movement involved. Intelligent measures toward educating the public to drive safely can only be taken when the performance of driving an automobile is thoroughly understood.