Speed Change Determination in Low Speed Impacts - A Comparison of Techniques

During vehicle collision testing an accurate measure of the pre- and post-impact vehicle dynamics is necessary for analytical purposes. Sensors typically used for measuring vehicle speed change in low-speed collisions include 5^th wheels, high-speed video, bumper-mounted load cells, and accelerometers. The method used is often based on equipment availability, the involved vehicles, and the type of tests being performed. The purpose of this paper was to quantify the relative accuracy of these four methods in aligned low-speed rear-end collisions. Data from 73 such collisions (clustered in two groups at target vehicle speed changes of 4 and 8 km/h) showed that all four instruments yielded statistically similar results for a target vehicle speed change of about 4 km/h, and that data derived from the 5^th wheel and high-speed video were different than data from the other two sensors at the 8 km/h level. When the data were analyzed for differences of 0.1 m/s (deemed an acceptable difference between sensors for the analysis of real-world collisions), there was no difference between speed change calculated by the four sensors.