Evans Accident Reconstruction


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Accident Reconstruction Example

Here is an exmple of an accident reconstruction based on a fictitious accident, which we will use to describe some of the techniques and tools used to perform an a actual accident reconstruction and to answer common questions. The vehicles photographed are vehicle that were utilized in an Evans Accident Reconstruction crash demonstration. This is a simplified explanation for educational purposes; an actual accident reconstruction is usually much more complex and goes into many more factors than are described here.

Our fictitious automobile accident occurred on Tabor Road, near the intersection with Alexander Road, in Bryan, Texas. Mr. Smith was driving a 1997 Pontiac Grand Am southbound on Tabor Road. A 1991 Volkswagen Jetta driven by Mr. Klaus was making a right turn from Alexander Road onto Tabor Road when the vehicles collided.

Some time had passed since the accident, and there was no debris or tire marks present on the roadway. There were orange police paint marks on the roadway marking the Area of Impact (AOI). There was also police paint marking the areas where the vehicles came to rest, both on and off the roadway. The evidence and the roadway were measured with survey equipment. Other items of interest such as telephone poles (often used as reference points in police measurements), buildings (where potential witnesses may have been watching), and potential visibility obstructions (such as signs, trees, etc) were also surveyed. Photographs were taken to document the accident site.

A scaled drawing of the accident scene was then drawn in AutoCAD:

CAD drawing of accident site

Next the vehicles were inspected. The vehicles were photographed to document the damage and other factors that could prove to be important. At this stage, if a vehicle has an airbag system that records data, and permission to download the vehicle is granted, then the data is downloaded, as it was in this case.

Pontiac - post-impact Jetta post-impact Airbag deployed
CDR imaging CDR data

Sometimes there is a potential issue with a vehicle that could have played a role in the accident, such as a tire, steering, or brake failure. In those cases a more detailed inspection may be performed in which vehicle components are thoroughly examined.

Each case is handled differently depending on the nature of the accident. The amount of crush on a vehicle can be measured to help calculate the forces at impact, such as speeds at impact. The amount of crush can also be measured using photographs and a photogrammetry program like PhotoModeler.

Jetta profile photo 1 PhotoModeler points PhotoModeler image 3D rendering

At this point in the reconstruction, the vehicles are drawn to scale and placed into contact positions based on their damages.

CAD drawing - Vehicles at impact

The vehicles can also be placed in their rest positions as measured at the accident site.

CAD drawing - Vehicles at rest

Vehicle data is entered into a computer program that can take into account the energy used to crush a vehicle at impact, momentum, and vehicle drag factors (the friction slowing the vehicles down on and off the roadway). Using the known impact position and rest positions, the computer model can be run to find the speeds of each vehicle at impact.

SMAC vehicle paths SMAC vehicle crush

Hand calculations can be performed to verify that the speeds from the computer model are reasonable. The computer model can also be compared with data that may be stored in the vehicle.

Once impact speeds are known, the focus turns to the vehicles’ movements prior to impact. Is there driver or witness testimony? Any evidence of braking on the roadway? A multitude of factors are considered.

Once the accident variables are understood, a report may be written to document the findings. The report may then be submitted to the court as the expert witness report.

A computer simulation animation, a very powerful tool for communicating different aspects of an accident, may be made. In animations, difficult time and distance concepts can be made clear. Views can be shown from inside a model of a vehicle to show what the driver could or could not have seen, and vehicle damages and motion can be illustrated. They can be invaluable in helping jurors clearly “see” an accident.

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