Thorn Consulting Services - Certified Accident Reconstructionist

Speed From Skidmarks

Skid MarksAfter an accident occurs, everyone wants someone to tell them what happened. But in fatal car accidents, sometimes nobody is left to tell. So we are left with just the evidence on scene. A big piece of that evidence is the tire skidmarks left on the roadway. In a majority of accidents, there are usually some types of tire marks left by the vehicle(s) involved. But there are different ways of solving speeds depending on the type of tire marks left behind. Is the evidence skidmarks, yawmarks, acceleration scuffs, flat tire marks, or imprints? Thorn Consulting Services has extensive experience in recognizing and determining the speeds of vehicles from the aforementioned marks.

It is well known that when a driver applies the brakes really hard, the wheels will lock. As a result, the vehicle will slide and usually leave evidence of skidmarks on the roadway. The length of these skids is an indication of the speed of the vehicle. Two factors are important when calculating speed from skidmarks: 1) the distance the vehicle slid and 2) the coefficient of friction or drag factor between the road and the tires of the vehicle.

If you know or have an estimate of how far a vehicle slid and the coefficient of friction, click on the above Skidmark Chart to find its speed. The chart assumes 100 percent braking efficiency on a level surface.

Download a Sample Speed From Skidmarks Chart. You will need to have Adobe Reader on your computer to view this file - download the FREE Acrobat Reader if you do not have it. It's very quick and easy.

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Thorn Consulting Services - P.O. Box 48482 - Spokane, WA 99228-1482
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Professional
Associations

ASME
Accident Reconstruction Network
Washington Association of Technical Accident Investigators
Society of Automotive Engineers

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The Accident Reconstruction Communications Network
Please email the ARC Network for any technical questions.

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