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“Speed (and more) From Video”

James R. Schmidt, Jr., BSME, Sr. Collision Reconstruction Engineer

Surveillance cameras are becoming increasingly more prevalent in today’s world, and videos from these surveillance cameras are oftentimes invaluable to an accident reconstruction analysis.

In this example, the movement of a municipal trash truck is captured by a residential video doorbell. This is just an example, as the trash truck was simply making its routine weekly pickup and was not involved in a collision. We sharpen our skills by evaluating such videos for practice.

Surveillance Trash Truck

As you’ve likely seen in our other examples, we can evaluate the speed of a vehicle from video, even if the video shows only a fraction of a second of the vehicle’s movement. In this example, we’ve evaluated average speed of the trash truck as it moves from one stop to the next. Inherently included in this evaluation is the distance the truck traveled over this same time period, being that speed is calculated from distance divided by time. Truck acceleration from a stop and deceleration back to a stop could also be calculated, if necessary. You can see the acceleration in the increasing speed at the beginning of the plot, then the speed tops out at about 8 mph, after which the speed decreases, which is the deceleration heading toward the next stop.

Charts

This analysis was done from video alone. We did not inspect the site, nor did we inspect the vehicle. Instead, an educated approximation of the distance between the rear drive axles on the truck was made, after which cumulative distance traveled and speed versus time were evaluated.

A simple evaluation with very refined results. For this example, distance traveled is accurate to less than 1 foot, and speed is accurate to within about 1 mph.

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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