Accuracy of Speed Change Measured by Event Data Recorders during Oblique Offset Frontal Impacts

Data downloaded from event data recorders (EDRs) integrated into the airbag systems of passenger vehicles can be key evidence for collision investigators. Often the EDR data includes information about the severity of the collision in terms of the longitudinal and lateral speed changes experienced by the vehicle. Previous studies have shown that for collisions with small lateral speed changes, the accuracy of the reported longitudinal speed change varies with manufacturer and magnitude. The goal of this study was to quantify the accuracy of EDR-reported speed changes in high-speed angled collisions with larger lateral speed change components. Data from 25 crash tests conducted for the National Highway Traffic Safety Administration’s (NHTSA’s) Oblique Offset Frontal Impact Research and Development Program were used in this study. The accuracy of the EDR-reported speed change was evaluated by comparing it to the longitudinal and lateral speed changes integrated from the independent reference accelerometers at the vehicle’s center of gravity. For vehicles with EDRs that also reported acceleration data, the speed change calculated by integrating the EDR-reported acceleration data was also compared to the speed change integrated from the reference accelerometers. The largest errors were seen in the two 2015 Honda Fit tests that under reported the longitudinal speed change by about 10 km/h. Although the average differences between the EDR-based speed change and the reference speed change were not significantly different from zero, the range of errors was large and varied between the different methods of extracting speed change and between the different components of the speed change The errors on EDR-reported longitudinal and lateral speed changes led to errors on the resultant speed change of up to 12 km/h under or 5 km/h over the actual speed change. The absolute errors for the longitudinal and lateral components of the speed change were similar but their relative errors were not. The speed changes computed by integrating the EDR’s acceleration data were on average less accurate than the speed changes reported and tabled in the EDR reports. The errors on the resultant speed change calculated from integrating the EDR-reported accelerations were up to 18 km/h under or 10 km/h over the actual speed change. There was considerable variation in the accuracy for different vehicle makes and models, with the largest errors observed in some Honda vehicles. The results of this study improve our understanding of the accuracy of EDR-reported speed change in high-severity angled collisions.