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 vehicle 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 a frequency that varies with the test vehicle’s speed. Investigating the origin of this frequency revealed the horn effect phenomena, which has been well known in 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 in prior research. The purpose of this study was to outline, test, and confirm the source of the wheel speed frequency as a valid method in forensic application. Data collection included the use of commercially available dash cameras, a pair of remote microphones to identify the source of the frequency varying with vehicle speed, and a VBox Sport to establish a ground speed baseline. The reliability of the audio data was compared against speed data collected from a baseline. The post-processing was conducted using iZotope RX to identify the frequencies of interest that were used to compute the vehicle speed and were compared with the ground speed baseline. The proposed method can be useful in addition to the prior published audio analysis methods to determine vehicle speed and other critical events of a vehicle for accident reconstruction purposes.