A vehicle in motion traveling 55MPH will travel about 80 feet per second. If you remove the reaction and perception times you still get about 360 feet to stop. That said, there are many factors relative to stopping distances. Condition of the roadway, weather, surface material of the roadway, whether your tires lock up or not, can add significantly to the braking distance. The alertness of the driver, the reaction time etc also play a part. A NASCAR/Indy driver will have a significant lesser reaction time, in most instances, than one of us retired old f#$ts. OTOH, they usually drive significantly faster than we do.
