Inertial Pedal Displacement and Brake Switch Activation in Frontal Crash Events

This paper presents research into the inertial displacement of brake pedals and the subsequent activation of brake light switches during crash events. In certain scenarios—such as multiple-impact crashes or with pre-impact interactions such as curb strikes or sideswipes—inertial forces alone may generate sufficient brake pedal movement to trigger the brake switch, activating the brake lights. Such signals may be recorded by an Event Data Recorder (EDR) or observed by witnesses and mistakenly interpreted as an indication of intentional driver braking. To investigate this phenomenon, HYGE sled tests were performed using brake pedal assemblies and associated components from a Toyota Tacoma pickup truck and a Cadillac DeVille passenger sedan. The assemblies were subjected to acceleration pulses simulating a frontal impact, with high-speed video used to capture brake pedal displacement and brake light activation. The tests demonstrated that inertial loading from a pulse with a delta-V (change in velocity) as low as 12 mph could result in momentary brake light activation due to pedal displacement from inertial forces. Increasing the magnitude of the acceleration pulse produced greater displacement of the brake pedal and extended the duration of the brake light activation. An example is presented that demonstrates inertial pedal movement in a full-scale vehicle test conducted by striking a curb, which resulted in brake light activation with a delta-V considerably less than 12 mph. Additionally, a field survey of 50 passenger vehicles found that the brake switch activation threshold ranged from 0.25 to 0.56 inches of pedal travel for 80% of the vehicles measured. These findings indicate that relatively small crash accelerations and durations can produce sufficient inertial pedal movement to activate brake lights, and that only minimal pedal displacement is required in most vehicles.