The McKeen Motor Cars were the first example of an all steel, self propelled train car design in the world. They were also the first known use of purposeful aerodynamic design in North America, and the first successful use of a motive power other than electric or steam, and in being so, they were the lead into the Diesel/Internal Combustion engine era.

The drop-center door invented by McKeen is still used in many trolley cars and buses today. The idea allows the best flow of traffic through two doors. The steps for getting up inside were recessed inside the body of the car, preventing snow, rain, hail, ice, dust, and other things from getting inside like the permanently open Pullman coaches. The Pullman coaches also had the doors on the ends of the car. This meant that in a collision with another train, the doorway would get crushed, and passengers were stuck inside until a hole was opened. McKeen put the door in the center where minimal collapsing would occur.

The knife-edge nose and semi-circle aerodynamic design was tested by the Germans and showed great reductions in drag. It wasn’t until years afterward that the the round shape was moved to the front, and the point to the back, which, ironically, proved more efficient

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