Blue Line

The science behind collision reconstruction

November 11, 2014  By Daniel Carrier

There is a popular misconception that the analysis of physical evidence is the most important and critical role in investigating fatal or life threatening collision.

All investigations involve collecting evidence, corroborating it from as many sources as possible and proving the facts at issue. Witness evidence cannot be underestimated. There is great value in witness, victim and accused statements.

A properly conducted interview is invaluable. Always ask yourself the following questions:

ò What information do I have?


ò What information do I need?

ò Why do I need the information?

ò How do I get the information in a manner that can be used in judicial proceedings?

ò What evidence would the extra information offer?

ò Have I exhausted all my sources of potential information?

Investigations can often get caught up in the details and lose sight of the goal. This can be particularly frustrating during the course of a trial. William of Occam (1287û1347) gave us a means to avoid the quagmire of possible scenarios. Occam’s Principle states that among competing hypotheses, the hypothesis with the fewest assumptions should be selected. In essence, he is telling us not to over complicate things.

The best definition I’ve heard of Occam’s Razor was from a criminal court judge, who said, “If you hear the sound of hoof beats approaching, don’t look for a duck.”

An investigation involves much more than the collection and analysis of physical evidence, which can be misinterpreted. Reconstruction is usually limited to collisions resulting in death or life-threatening injuries. These are always tragedies with massive emotional “shock-waves.” Any investigation into such matters requires competence in all facets of investigation.

In my new book, I lead the reader through the science behind collision reconstruction techniques currently being used in the field.

In order to understand the scientific analysis, it is advantageous to develop an understanding of background information involving collision investigation. As a result, this book is organized so as to cover the following progression:

ò Series of events surrounding collisions

ò Vehicle dynamics

ò The physical evidence at the scene of a collision

ò The recording of physical evidence

ò The analysis of physical evidence

ò The reporting of the analytical findings

There is a significant mathematical component involved in any discussion of the physical sciences. In an effort to ease the reader into the science, I have included a review of the mathematics involved in the analysis discussed but limit the math concepts to those directly related to the analyses that follow. I do not cover math concepts that are merely “nice to know”.

Since police testify as witnesses for the prosecution and their equivalents on the defence team are often engineers, the book was designed to provide a common language between all parties involved in the analysis of collision reconstruction evidence.

True knowledge is built by understanding the principles behind the analysis. Information must be digested in the mind and integrated into practice and analysis. My book is meant to be a valuable reference to those already in, or preparing to enter, the collision reconstruction field.

While it is beyond the scope of my book to cover all areas of an investigation, I can leave you with one thought that may assist in developing an investigative strategy. All major collisions requiring reconstruction should be handled as sudden death as opposed to collision investigations.

The conclusion of the investigation may result in traffic related charges, but the investigation should be conducted as an undetermined death investigation; the living owe as much to the dead.


Daniel Carrier is a 26-year member of the Peel Regional Police, including five years on the collision reconstruction team, and is currently a role specific trainer. His book, is available from <>. Contact:

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