Something has to be said about an engineer willing to stand infront of a car during a brake test. In 1951 there was not a DOT or NHTSA setting standards for braking distances. A lot of the testing took place on a big hill outside of Shanksville, PA. If the engineer and car survived the decent down a long grade, the car passed.
After WWII, automakers wanted to be more scientific so they could test the effectiveness of changes to the linings, drums and hydraulics. So was born the mechanical pedal applicator. The pedal produced a constant force that could be repeated over and over.