Always, Always, Always… Start with the Physical Evidence

Skid Marks

Robert T. Lynch, P.E., Principal Collision Reconstruction Engineer

As collision reconstruction engineers, we are charged with the task of applying the laws of physics to the physical evidence that remains following a collision to determine, if possible, how a collision occurred. This physical evidence can exist in many forms, including scene photographs, police measurements, vehicle and site inspection data, event data, and surveillance video of the incident. Utilizing the physical evidence, we then attempt to piece back together (i.e.- reconstruct) how the collision occurred.

There are times when the physical evidence from a collision is limited, and a complete reconstruction is not possible. In those instances, we are often left to evaluate secondary evidence in the form of witness testimony. However, witness testimony is not always accurate and thus testimony, by itself, cannot be accepted as the foundation for an expert opinion. Instead, we may analyze the estimates provided by a witness to see if the testimony is consistent with the physical evidence that we do have from the collision.

Where a forensic expert can go awry is when they focus too much on the witness testimony, and then reject the physical evidence because it does not align with the testimony. This flawed methodology is not proper science and has no place within the field of collision reconstruction. An expert must first analyze the physical evidence to form the foundation of their opinions, and then evaluate the testimony, rejecting those positions of the testimony which are inconsistent with the physical evidence (even if the testimony is from the party we represent).

Note: This article is dedicated to my dear friend and colleague, Steven M. Schorr. Whenever I had a question regarding a reconstruction, he would bring it back to the basics and remind me to always look at the physical evidence first to form opinions, and worry about the testimony last. I miss you Steve.

Categories: Collision Reconstruction | Physical Evidence | Robert T. Lynch


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