Tag Archives: James R. Schmidt

“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.

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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:

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An Example of Off-Tracking


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

A tractor-trailer making a turn undergoes noticeable off-tracking. Specifically, the trailer tires track well to the inside of the path followed by the tractor tires. In this real-world example, a tractor-trailer was making a tight right-turn at a busy intersection. The turn was close to, but a bit less than, 90 degrees. The turn was captured on a dash cam, from which a series of still images have been saved.

First, the tractor-trailer (at the right side of the photo) approaches the intersection:
Off-Tracking

Then, the tractor swings wide:
Off-Tracking

…and makes its turn:
Off-Tracking

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Captain Video and the 3 Car Scenario


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

By now, you’ve likely seen our speed from video evaluations. It doesn’t matter whether it’s a still camera, a moving camera, a dash cam video, daytime, or nighttime. If we can identify sufficient points of reference, we can evaluate speed of a given vehicle from video.

In this example, we’re evaluating speed of three vehicles from one clip: 1) the vehicle equipped with the dash cam (vehicle 1); 2) the vehicle a distance ahead of vehicle 1 (vehicle 2); 3) a vehicle travelling in the opposite direction (vehicle 3). We are able to assess additional vehicles, if that were necessary.

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Speed from Video – Captain Video’s Specialty


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

I’m a collision reconstruction engineer with over 23 years of experience in the field. I’m affectionately known in the office as Captain Video, given my love for the evaluation of vehicle speed and crash-related parameters from surveillance videos.

Basic evaluation from stationary camera:

A 2019 Toyota Sienna minivan passes in front of a stopped dash cam. Speed from video is evaluated therefrom. Speed is distance over time. The easiest way to perform the evaluation is to look at the timeframe required to travel the vehicle’s wheelbase (i.e. the distance from the front wheel or axle to the rear wheel or axle). So, in this example, the minivan travels its 119 inch wheelbase in 7 frames of a 30 frame-per-second video. Distance is 119 inches, or 9.92 feet. Time is 7 frames divided by 30 frames per second, or 0.233 seconds. Calculating speed … 9.92 feet divided by 0.233 seconds is 42.5 feet per second, or ~29 mph. FYI, this was a 35mph speed limit roadway.

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Collision Reconstruction Tidbits


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

A vehicle traveling 50 miles per hour (73.3 feet per second) emergency brakes to a stop on a dry roadway in 119 feet. That same vehicle traveling down a 5% grade, for example, takes longer to stop, as the downgrade effectively reduces the friction. The braking distance for that vehicle would be 128 feet. When traveling uphill the opposite is true, as the uphill grade (again, assuming 5%) effectively increases the friction, resulting in a braking distance of 111 feet. The higher the friction, the quicker a vehicle can stop. The lower the friction, the longer it takes a vehicle to stop.

Speed from video can be an easy thing to evaluate. Of course, we must be able to see the vehicle of interest and the video needs to be of a good quality with a constant/known frame rate. Speed is simply distance divided by time. For example, if a vehicle travels 100 feet in 1.37 seconds, its speed is 73 feet per second (or approximately 50 mph). Alternatively, if the view of the vehicle is limited to something small, or just a “blip”, the time it takes the vehicle to travel its wheelbase (i.e. distance from front axle to rear axle) can be used. For example, a 2007 Honda Odyssey minivan passes through the field of view of a surveillance camera, and in doing so it travels its wheelbase of 118 inches (9.83 feet) in 4 frames of a 30 frame per second video (0.133 seconds). Speed is calculated at 73.8 feet per second (or approximately 50 mph). Each case is unique, and evaluations ranging from simple to complex, using traditional to advanced 3D computer-aided methods, can be performed to determine speed and many other parameters that may be of interest.

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