Speed Determination Using Audio Analysis of Dash Camera Video from Passenger Vehicle Tires Frequencies for Vehicle Accident Reconstruction

Prior research has validated a reliable method of determining speed using the audio data and a known wheelbase of a test vehicle captured by dash camera audio. However, it has been found that dash camera audio may record an unknown frequency that varies with the test vehicle’s speed. Investigating the origin of the unknown varying frequency revealed the horn effect phenomena, which has been well known research by the tire industry. Independent research identified a frequency generated by the rotating tires when a certain speed threshold was reached by the test vehicle. The research concluded that the tread pattern of the tire in contact with the roadway surface generated a frequency that varied with vehicle speed. However, research using the audio from a dash camera to determine vehicle speed from that specific varying frequency for forensic purposes has not been investigated. The purpose of this study was to outline, test, and confirm the source of the varying frequency as a valid method in forensic application. Data collection included a commercially available dash camera, two GoPro camera’s, and a pair of remote microphones to identify the source of the frequency varying with vehicle speed. The reliability of the audio data was compared against video and speed data collected for a baseline. The post-processing was conducted using iZotope RX, a recognized audio software, to identify and compare the frequencies of interest with the audio baseline. The proposed method can be useful in addition to the prior audio analysis method to determine vehicle speed and other critical events prior and post collision of a vehicle accident reconstruction.