Accident Investigations: Determining Speed Using Drag

By Michael Miranda

The term “Drag Factor” is not mentioned in engineering mechanics or physics books but it is invaluable when investigating traffic accidents. Drag Factor is the deceleration coefficient for an entire vehicle. The Coefficient of Friction is the deceleration coefficient for a sliding tire. The Drag Factor and Coefficient of Friction are the same, if and only if, all four tires of a motor vehicle are locked and sliding on a level surface.

For years police officers were taught these two terms were the same thing and for the sake of simplicity, we will use the terms interchangeably and say they mean the same thing for the purpose of this discussion. In this article, the drag factor, or coefficient of friction, basically measures the stickiness of a surface such as a roadway, a grassy knoll, a ditch, and the like.

So why does an accident investigator need to know what the drag factor of a roadway surface is and how do they use it? Each surface has its own drag factor, which will determine how quickly a vehicle can come to a stop and how far it will travel while doing so. This answers the question: “How fast were they …read more

Source:: Private Invest