H. Clifford Brokaw, Putnam's Automobile Handbook: The Care and Management of the Modern Motor-Car
“ As a matter of fact the foot should instinctively go to the brake pedal each time the hand goes to the horn. But if you are seen by the other person why blow the horn at all?If one is driving along a country road and desires to pass another car going in the same direction, it is customary to sound the horn once that the driver ahead may not turn his car in front of you, and so that, if needed, he may turn to the right to let you pass on the left. He is the judge as to when and where he will turn, since he can see ahead better and knows what obstructions are to be avoided. ”
