Determining Vehicle Speed from a Video Recording

CCTV video is typically used to provide information about what occurred during a noted event and to assist in identifying people, vehicles, objects, etc. A less common but equally helpful use of CCTV video is to determine the speed of vehicles traveling through the field of view. This article summarizes the legal and evidential requirements that must be met to successfully use this type of evidence in court.

I will discuss this topic by referencing a Canadian case that illustrates how to correctly present this evidence in court. In R. v. Sakhon, 2024 BCPC 9 (British Columbia Provincial Court), the defendant was charged with several offences arising out of a motor vehicle collision. One of the issues was the speed at which the defendant’s vehicle had been travelling immediately prior to the collision. This case illustrates the complementary roles that a certified forensic video technician and a collision reconstruction expert play in acquiring and analyzing relevant data.

The video technician was requested to determine the frame rate for three segments of video obtained from a business CCTV system. The technician was given a disc with the video files and recognized that due to the file format (AVI), she had not been given the original proprietary format videos. Pursuant to her request, she was provided with the AVE files and the Avigilon player. With this media and player, the technician was able to advance the recording frame by frame and determined the frame rate to be 20 frames per second and further noted that there were no duplicate or missing frames. The video recording depicted three vehicles of interest passing through the field of view and the technician determined the number of frames each vehicle remained in view.

By examining the video recording, the collision reconstruction expert identified fixed objects that needed to be measured to determine the distance between them. Using a 3D digital scanner, an officer assisting the collision reconstruction expert measured the scene. Reference to still images from the CCTV video allowed the expert to determine the distance travelled by the offending vehicle from one reference point to another. Utilizing the distance travelled and frame rate, the collision reconstruction expert determined that over a distance of 24.37 meters and a time of 0.75 seconds, the speed of the vehicle was between 110-116 km/h (in a 50 km/h zone).

The defence argued that the speed determination was unreliable, and speculated that the frame rate calculation had an undetermined margin of error, the video may have been compressed, the 3D scanner was not properly calibrated, and the CCTV camera may have been moved. No evidence was called on these points, and in particular no expert evidence. The Court accepted the speed evidence to have been validly and reliably proven by the combination of the evidence of the video technician, the officer who conducted the 3D scan of the scene, and the collision reconstruction expert. For this and other reasons, the defendant was convicted.

Commentary

This case is not ground-breaking. It is however a good example of how determining the speed of a vehicle traveling through a video recording’s field of view should be calculated. First, the video recording must be authenticated by establishing location, date, time, and image integrity. Second, a person suitably qualified in video technology should assess whether the best video recording format has been provided, whether compression is a factor, and the frame rate. The technician should also determine whether there are any factors that might render the recording unreliable for speed calculation purposes. Third, a suitably qualified person should measure the scene depicted in the video recording. The video technician can assist in properly placing the vehicle of interest within the measured scene at relevant points and in determining the number of frames involved. Finally, the collision reconstruction expert analyzes all this data to determine vehicle speed.

There are cases where determining vehicle speed has been performed incorrectly or unreliably. These cases may falter for several reasons. If a collision reconstruction expert attempts to do all this work but is not suitably cross-trained in video technology and analysis, the expert will not be able to competently address issues such as correct file format, compression, real versus predictive frames, and other technical issues. If the video foundation is not solid, the speed measurements will have weakened support. Similarly, if the video technician does not ensure that they are working with the best quality original file format, the reliability of their evidence will be compromised. In some cases, a reverse projection experiment would be valuable – this is accomplished by driving a vehicle through the field of view of the same CCTV camera at known speeds and comparing those recordings and measurements to the original video recording.

Recognizing that different skillsets are required to properly determine the speed of a vehicle observed in a video recording shows humility and a desire to provide robust evidence for the court to consider. Anecdotally, I have noticed that some engineering firms are having some of their staff trained in video technology and analysis so that this work can be done in-house. This approach demonstrates a good understanding of the need to devote trained resources to each aspect of a speed determination project.