Evaluating Vehicle Speed From Video… It Never Gets Old For Me!


James R. Schmidt, Jr., BSME, Sr. Collision Reconstruction Engineer
Dash cam video from a vehicle traveling westbound on State Route 372 in Holtwood, Lancaster County, PA was evaluated for vehicle speed. Several stills from the video are shown below:

Thirty-five points of vehicle position were plotted on an aerial photograph, covering more than 1 minute and 1.1 miles of travel of the vehicle across the Norman Wood Bridge over the Susquehanna River, and partially up the windy hill on the other side.

First, vehicle speed from the plotting was calculated, and a graph of calculated vehicle speed versus time was made:

Then, a graph of GPS speed versus time as displayed on the dash cam video was made:

Using GPS speed as the baseline for comparison, the calculated vehicle speed versus time plot was laid thereon:

An excellent match (within 1 to 2 mph) was obtained over the length and duration of the plotted vehicle movements. Those results are incredible! And that’s what we can do and the accuracy we may be able to obtain when evaluating vehicle speed from video for you!
James R. Schmidt, Jr., BSME, Sr. Collision Reconstruction Engineer with DJS Associates, Inc., can be reached via email at experts@forensicDJS.com or via phone at 215-659-2010.

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