This paper introduces a method for calculating vehicle speed and uncertainty range in speed from video footage. The method considers uncertainty in two areas; the uncertainty in locating the vehicle’s position and the uncertainty in time interval between them.
An abacus style timing light was built to determine the frame time and uncertainty of time between frames of three different cameras. The first camera had a constant frame rate, the second camera had minor frame rate variability and the third had more significant frame rate variability. Video of an instrumented vehicle traveling at different, but known, speeds was recorded by all three cameras. Photogrammetry was conducted to determine a best fit for the vehicle positions. Deviation from that best fit position that still produced an acceptable range was also explored. Video metadata reported by iNPUT-ACE and Mediainfo was incorporated into the study.
When photogrammetry was used to determine a vehicle’s position and speed from video recorded by a constant frame rate camera, the results closely matched the speeds reported by the instrumented vehicle being measured. This low uncertainty resulted from the constant frame rate eliminating error in time, and from low error in the vehicle’s position through photogrammetry. For the variable frame rate camera, uncertainty in speed was dependent on the time between frames analyzed as well as any uncertainty in position. Quantification of this uncertainty has value for the reconstructionist. Determining speed of the vehicle in the variable frame rate video could be improved by incorporating frame timing reported by iNPUT-ACE or through other video analysis techniques and software that measure precise time differences between each frame.