Collision Reconstruction – A Desktop Analysis Approach

Skid Marks


Robert T. Lynch, PE, Senior Collision Reconstruction Engineer ::::
Some cases don’t reach our desk until months or even years after the incident and the physical evidence that is created immediately after the collision is, at times, long gone. Any potential roadway evidence such as tire marks or gouge marks may have vanished, or the road has been repaved and the vehicles may have been repaired, or totaled, and sent to a salvage yard without a trace.
For these instances, vehicle and/or site inspections may not be feasible, or they would not be expected to provide any data that would be substantial to the reconstruction. That is, an inspection of a repaired vehicle would not be as useful as photographs displaying the damage from the collision, and although an inspection of a resurfaced site would provide roadway widths and other measurements, no roadway evidence would be expected to remain after such a long period of time.
In these cases, a preliminary desktop analysis may be warranted to determine the specifics of the collision based on the available data. If the data is sufficient, this can be done as a stand- alone analysis or as a way to evaluate ‘the good, the bad, and the ugly’ of a case prior to the client incurring the additional costs associated with field work (i.e. inspections). The preliminary desktop analysis will often determine the need for any field work that is necessary to complete the reconstruction analysis.
For example, we were recently contacted by a client representing the driver of a vehicle that executed a left turn from a side road in front of another vehicle traveling on the thoroughfare (that had the right-of-way). Both vehicles contained event data recorders that stored crash data associated with the collision. The police imaged the data as part of their investigation, which was provided for our review.
The event data from these two vehicles, as with most newer model vehicles, provided 5 seconds of pre-impact speed, acceleration, and braking data. The client wanted to know specifically if his driver had stopped at the stop sign before pulling out, while also wanting to know if the speed of the other vehicle was a contributing factor. An analysis of the event data showed that the client vehicle slowed for the stop sign; however, did not come to a complete stop before entering the intersection. The data also revealed that the other vehicle was traveling 15 miles per hour above the speed limit. Had that vehicle been traveling at the speed limit at the point in time when the client vehicle pulled out into the intersection, the client vehicle would have cleared the travel lane before the other vehicle reached the point of impact.
So, while the client vehicle created the hazard that led to the collision, the speed of the other vehicle was a contributing factor to the collision. With the results of the desktop analysis, which was performed at a significantly reduced cost to the client, as opposed to a full reconstruction with associated field work, the client was better equipped to make arguments at the arbitration and, in this case, reach a favorable settlement.
Robert T. Lynch, PE, is a Senior Collision Reconstruction Engineer with DJS Associates and can be reached via email at or via phone at 215-659-2010.

Categories: Collision Reconstruction | Collision Reconstruction Engineer | Robert T. Lynch

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