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Accident reconstruction is the application of scientific principles to interpret and analyze the evidence left after a crash has occurred. The analysis answers questions about how and why the crash happened and if it was possible for the collision to be avoided entirely.



The following case study examines a real-world crash and illustrates some of the questions that a reconstruction analysis can answer.


Crash Scenario           


As a Scion FR-S slowed and stopped to allow oncoming traffic to pass before making a left turn into a business driveway, it was hit from behind by a Toyota Corolla. The Toyota driver admitted to police that he was searching for directions and was looking down just before the crash. Both vehicles sustained disabling damage and were towed from the scene. A reconstruction analysis was conducted to determine how fast the Toyota was traveling when it struck the Scion and to assess whether the Toyota driver could have avoided the collision. 




Photographs and measurements of the accident site were taken the day after the crash. A short set of skid marks and the remnants of a fluid stain were the only physical evidence remaining on the roadway. The crash site was later scanned with a 3d laser scanner to document the overall geometry of the roadway.


An inspection of the Scion was conducted and data from the vehicle’s airbag control module (ACM) was imaged. The ACM in this vehicle, as in many modern vehicles, includes an event data recorder (EDR) function. Sometimes referred to as the "black box", the EDR saves data measured by vehicle sensors over a short time period leading up to and including the collision. The Toyota in this case was an older model and was not equipped with an EDR.



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The EDR data from the Scion started approximately 5 seconds prior to the crash, detailing the vehicle’s speed and driver inputs leading up to the impact. The data also included the delta-V measured by the vehicle’s ACM. Delta-V is the vehicle’s cumulative change in velocity over the short duration of the collision and is a quantitative measure of the crash severity.

Analysis of the data established that the Scion slowed normally and came to a stop from an initial speed of about 20 mph over the 5 seconds prior to the crash.  The driver had the brake applied, and therefore the brake lights illuminated, for at least 5 seconds before the crash. The Scion was completely stopped for about 0.5 seconds before impact.  

A computer simulation of the crash was prepared to establish the impact speed of the Toyota. The simulation calculates the motion of the vehicles using mathematical models of vehicle dynamics and impact mechanics. Combining the physical evidence from the site inspection, the EDR data from the Scion, and the simulation results, the speed of the Toyota at impact was found to be approximately 18 mph.  

Factoring in the skid marks leading to impact, the Toyota was traveling at about 30 mph when the driver started braking. The length of the skids established that the Toyota driver applied maximum braking for only about half a second before impact.  



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The reconstruction analysis established that the driver of the Toyota had at least 5 seconds to observe the Scion's brake lights and speed reduction. This was ample opportunity for a reasonably attentive driver to come to a stop or change lanes to avoid this collision. The Toyota driver’s distraction and inattention to the traffic ahead caused this collision.  

The video below shows a sample visualization of this event from the 3d simulation that was prepared during the reconstruction analysis. The crash event can be shown from multiple angles, including driver or witness perspectives.

Please contact 4Moto Engineers to discuss how we can assist with an accident reconstruction investigation and analysis.

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