Sometimes referred to as collision investigation or crash causation, Traffic Accident Reconstruction is the analysis and interpretation of post-collision scene evidence using scientific and empirical methods to determine what sequence of events led up to or caused the accident.   Often it is desired to determine the “delta-V”, or the change in velocity of the vehicles during the impact phase of a crash in order to correlate the acceleration loads (sometimes noted in g’s, the number of times the force of gravity) with injuries to the occupants of the vehicle.

Accident reconstruction work is very much like trying to form an unknown picture from a puzzle missing most of its pieces.   Some of the pieces can be gleaned from roadway evidence such as skid marks and gouges, some from vehicle damage profiles or event data recorders, or possibly from witness statements.   Inevitably, some of the pieces of the puzzle will never be found.  But usually enough pieces can be found to reveal a satisfactory picture to the analyst that solves the puzzle to a reasonable degree of certainty.

Determinations of such issues as “how fast was the defendant going?” may not be answered with an accuracy of one mile per hour, but often can be ranged to within plus or minus 5 or 10 mph.   The better the quality of the evidence, the more specific and accurate the answers can be.

The best evidence would be excellent scene and vehicle preservation in situ.   But roadways need to be opened to traffic quickly, vehicles may be damaged during extrication procedures, and vehicles need to be hauled away, so such a high level of preservation is not normally practical.  Usually the police, being first on the scene, are in the best position to document the details of the crash scene, before vehicles are moved, skid marks fade, etc., and sometimes this is done.  But often only cursory or no documentation is done.

After some time has elapsed, the best evidence we can usually hope for is excellent scene documentation from the time of the incident via accurate measurements and high-resolution photographs (usually obtained from police reports, insurance documents, shop estimates, etc.), and some preservation of the subject vehicles (usually in a tow yard) for later inspection and analysis.  But it is not unusual for cases to be submitted to an accident reconstructionist years after the accident occurred.  The roadway may have been repaved or completely re-aligned in the meantime and the vehicles long since repaired or recycled, so we may be left with little more than photos of the vehicles and/or scene, or even less.   In some jurisdictions police will not even respond to “non-injury” accidents, so if you are involved in an accident and can SAFELY (staying out of traffic lanes, etc.) take photos of the overall scene and the relative locations of major roadway evidence (skids, debris, vehicle points of rest) before the scene is compromised, it could be very helpful should the accident later need to be reconstructed.   Even with limited information available, though, it is usually possible to determine most of the major characteristics of the accident sequence.


c 2014 Benn Karne