GO to the designated shelter, basement, or to an inside hallway at the lowest level of the building. STAY AWAY from windows. GET under a sturdy piece of furniture such as a workbench, heavy table, or desk - hold onto it. USE arms to protect your head and neck. If building shelter is not attainable, crouch near a strong building, and protect your head and neck as indicated above.
Tornadoes can change direction quickly, and lift up a car or truck, and toss it through the air.
Get out of the vehicle, and take shelter immediately. It was simple enough to use in daily practice without involving much additional expenditure of time or money. From a practical point of view, it is doubtful that any other system would have found its way into widespread accepted use, even to this day. The entire premise of estimating wind speeds from damage to non-engineered structures is very subjective, and is difficult to defend from various meteorological perspectives. Often times, we hear on radio and television weather reports that a tornado was an F1, F2 or greater.