FARO Ad Implies A Single Equation Adequate for Crash Reconstruction?

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MSI
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FARO Ad Implies A Single Equation Adequate for Crash Reconstruction?

Post by MSI »

Below we present an ad posted by FARO wherein a laser cloud scanner was used simply to present pictures of a crash. It included an incomplete crash reconstruction which apparently a driver agreed was OK.
  • Our summary, which is also repeated below is:
    • Laser Cloud Scan Devices for crash reconstruction by and others are excellent for memorializing and presenting crash scene data and vehicle crush measurements.
      However
      • As scientists, engineers and accident reconstructionists, we should not let the impressive presentation abilities of data from these scanners obscure our duty to perform a careful and detailed engineering analysis while also continually testing and evaluating the applied techniques, including computer programs, to achieve the most accurate reconstruction possible
Here is our response to the FARO ad about an incomplete analysis:
FARO AD PRESENTATION:
  • Saw a post on Linkedin Today on FARO's Linkedin Page which included:
    • "Calling all #TrueCrime and #ForensicScience fans: If all evidence from a fatal crash scene pointed to one driver being at fault, but the second driver had a very different story to tell...who would you believe?"
      FARO Case solved.jpg
      FARO Case solved.jpg (20.37 KiB) Viewed 89 times
      Which included the following:
      • "In our case study, one forensic scientist decided to use FARO technology to solve the mystery. Find out the twist ending: https://bddy.me/34Ok7tv
        With a link to FARO web page Modern Day Scherlock Holmes 3D Scanning Meets Forensic Science
        That page includes a link to a PDF report
        which includes
        • "At the scene of the accident, Survivor B’s car ended up on the wrong side of the road, facing oncoming traffic, while Party A’s car remained in its lane. The traffic police determined that Survivor B’s husband, who was driving at the time, should bear full responsibility for the accident.
        • "The 3D point cloud data enabled Prof Zhao to obtain accurate measurements and perform a precise deformation analysis on a computer. "
        • "Using the software, Prof Zhao found the positions of the two vehicles prior to the collision by pulling them apart. With this, the positional changes between the two cars (prior and after collision) were reconstructed. By substituting the trace data on the ground, Prof Zhao placed both vehicles in their relative positions.
        • Taking the collision point as the center, and calculating with an equation, he deduced that the intersection angle for the collision was 16 degrees."
MCHENRY DISCUSSION on FARO AD:
  • Apparently the 'driver' of the adverse vehicle "agreed with Prof Zhao’s "deduction" that it was indeed the truth of what happened"
    • We wonder if the driver 'agreed' or simply didn't know due to injuries, etc and once presented with the impressive scientific looking graphics felt they had no choice but to agree.
    • And the analysis MAY have been correct, it may have been WRONG...we have problems with any analysis using a SINGLE EQUATION to solve a complicated collision and hiding a simple single equation analysis behind fancy graphics, like those produced with laser cloud scans, it is simply unacceptable
    In our 50+ years of crash reconstruction & investigation expertise we have found that
    Fancy Graphics and Bluster many times mask inappropriate and incomplete collision investigations and analyses.
    • Cloud scan technology is amazing and being used in crash reconstruction to create great demonstrative documentation of crash scene details and vehicle damage details....however as with any new technology one must be careful to not let the 'pretty pictures' obscure the duty to fully and completely investigate and reconstruct a crash...
      • What is the singular "equation" Zhao used?
        • No doubt a simplified momentum analysis which assumes "instantaneous momentum exchange" which sometimes is OK,but can be a problem as it is EASY to GET ANY RESULT WITH SOME IMPACT CONFIGURATIONS, LIKE WRONG SIDE OF ROAD TYPE QUESTIONS. (see below for links)
      • What is the "precise deformation analysis on a computer"
        • A damage analysis of some sort? That would indicate more than one equation was used and many assumptions (what did he assume for each vehicle's stiffness characteristics? etc.)
          We have a Forum section on Damage Analysis which presents and discusses the limitations and preliminary characteristics of all CRASH type damage analysis procedures.
          Given the ad includes the statement that he used a 'single equation' one must conclude that NO DAMAGE ANALYSIS was performed except a geometric manual analysis. He visually and arbitrarily "pulling the vehicles apart" at some random rate and angle "on the computer" which is merely a fancy way to pretend there was some scientific calculation procedure aka "computer method" behind what he did to determine the approximate impact positions and orientations.To scientifically 'pull the vehicles apart" is a much more complicated process than that. He got lucky or the driver didn't know and so simply agreed with his determination. The paper does not present any scaled roadway evidence such as tire marks, debris, etc from which others might be able to check his work.
      Crash reconstructionists should try to test and refine any reconstruction findings and conclusions and use more than one "equation". A true simulation program like SMAC, which is equivalent to running a full scale mathematical test, is a good choice since it models the precise vehicle trajectories and collision interactions and includes collision forces and moments and damage approximations
      For example:
      • Zhao's "deduced intersection angle for the collision of 16 degrees" is rather high.
        Did he perform any analysis to determine whether and how the 16 degrees was created?
        • Using a program like SMAC which actually mathematically models the forces and moments of the collision interaction as they happen over 50-150 ms of the collision.
          The SMAC program can also be used to model the pre-impact movement which might have allowed Zhao to determine if the 16 degrees was possible
          • He should have determined as a minimum how much lateral distance was required to create 16 degrees with something like the Barrier impact angle Equation.
            16 degrees is a HIGH angle to produce in a single maneuver in the lateral space available.
            • Note that the ability of a vehicle to change its direction of motion is dependent upon its forward speed, the utilized roadway friction and the lateral space available for the maneuver. Were any pre-impact tire marks documented? where relative to the center of each lane was the approximate collision area? And relative to that where did the vehicles come to rest?
      These comments apply to any crash analysis in general and simplified momentum analysis in particular when applied to motor vehicle crashes.
      Programs like PC-CRASH, Virtual Crash, Planar Impact Models, and others:
    Summary:
    • Laser Cloud Scan Devices for crash reconstruction by and others are excellent for memorializing and presenting crash scene data and vehicle crush information.
      However
      • As scientists, engineers and accident reconstructionists, we should not let the impressive presentation abilities of data from these scanners obscure our duty to perform a careful and detailed engineering analysis while also continually testing and evaluating the applied techniques, including computer programs, to achieve the most accurate reconstruction possible
      Quote a slight variation from one in our McHenry Book and our Paper The Proper Use of Simulation Technology for Collision and Rollover Reconstructions and Highway Safety

    Here are items from the PDF report by Zhao:
    SHAOs pulling vehicle apart.jpg
    SHAOs pulling vehicle apart.jpg (44.63 KiB) Viewed 92 times
    ZHAOs scan of accident site.jpg
    ZHAOs scan of accident site.jpg (31.66 KiB) Viewed 92 times
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