“The Accuracy of Speed Captured by Commercial Vehicle Event Data Recorders”

Many newer commercial vehicles have an event data recorder (EDR) that can record pre-event and post-event speeds. The EDR is incorporated into the engines electronic control module (ECM). In this study, the accuracy of the ECM-reported speed was tested during acceleration, gear shifting and braking at speeds between 16 and 88 km/h (10 to 55mph). The ECM-reported speed was compared to the speed measured by a calibrated optical 5^th wheel. The results showed that the accuracy of the ECM-reported speed matched closely during acceleration, cycled to periods of under-reporting the speed during hard braking due to the ABS brake function, briefly under-reporting the speed after letting off the throttle for braking or gear shift and briefly over-reporting the speed near the end of a gear shift phase. This study also looked at calibration factors of the ECM and their effect on the ECM-reported speed. Information downloaded from an ECM after an accident event can be used in conjunction with conventional methods of accident reconstruction to evaluate the event. The downloaded information can expand the analysis of time, distance and speed because the ECM data covers a time duration of up to 105 seconds prior to the event and up to 30 seconds after the event. Current published research has only addressed the accuracy of event data recorders in passenger vehicles.