Should an Expert Rely Solely on PC-Crash for an Opinion?

General Questions related to the Momentum Based Analysis programs
#pc-crash #virtualcrash #crash
MSI
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Should an Expert Rely Solely on PC-Crash for an Opinion?

Post by MSI »

Q: I know that you have extensive knowledge and experience with simulation programs so I am hoping you might be able to help me out. I have an opposing expert who has relied solely on PC crash for his opinions. I know that PC crash is a momentum based simulation program but not sure what type of physics engine it is relying on for its calculations. The issue that I am wondering about is whether it would model a crash involving a 33000 pound trash truck versus 3000 pound car. I am still working on getting the inputs as they are dragging their feet producing those.
Any insight would be greatly appreciated!!


Our Response:
  • This forum has many topics and links about simplified momentum solution procedures like pc-crash, virtual crash and others.

    Main point is get the input file in printed AND paper form It is generally an easy task to ‘prove’ anything with pc-crash (or virtual crash, or planar impact models)
    What we have done in many cases is to get the input file(s) and make a simple change to the arbitrary and subjective user specified point and angle of momentum exchange and we "prove" a different opinion!!

    Demonstrates to the court how sole reliance on a computer program for an opinion can be fraught with issues
    • especially in your case with a 10:1 weight ratio
    We also recently encountered a person try to "prove" objectivity by using the "pc-crash optimizer" to prove that ONLY his version of the crash passed the optimizer!!
    • Well well...
      first of course the 'expert' made a judicious choice for point and angle of momentum exchange that ONLY worked for his opinion
      so what did we do?
      We simply changed the point and angle of momentum exchange and then could ALSO ‘prove’ a different opinion with pc-crash and also the 'pc-crash optimizer'!
      it all boils down to a judicious choice of arbitrary and subjective inputs for the 'point and angle' for the instantaneous momentum exchange.
    In a recent consulting case we were provided judgements from many Canadian cases related to the use of pc-crash in which it was either not allowed or dismissed as being not of any help to the court.
    For example a sample...(Note: we redacted the names of experts)
    • 2011 ONSC 4864, Ontario Superior Court of Justice, Lancaster (Litigation Guardian of) v. Santos
      which includes:
      • 54 The issue between the parties was as to whether EXPERT NAME REDACTED had sufficient expertise to use and utilize a computer programme called "PC Crash" to provide an accident simulation. The Plaintiff acknowledged that PC Crash is a reliable and accepted software tool.

        62 In Owens (Litigation Guardian of) v. Grandell, [1994] O.J. No. 496, 46 A.C.W.S. (3d) 796 (Ont. Gen. Div.), Kozak J. stated at paras. 31-32:
        • Although this Court was not called upon to deal with the admissibility of the computer generated video-graphic animation to supplement the reconstruction of the accident by the EXPERT NAME REDACTED, some judicial comment should be made as to the accuracy of this high-tech demonstrative evidence. If proven to be accurate, then it should be admitted like any other piece of demonstrative evidence, such as a chart or map. In considering what type of authentication is required, it should be proven:
          1. From the testimony from the accident reconstruction expert that the data points measured at the accident site were accurately recorded.
          2. From the testimony of the person who entered those data points into the program that they were entered correctly.
          3. That the algorithms used in the form and motion software validly apply the law of physics and validly render accurate images of the scenes depicted in the exhibit.
          4. Competent opinion testimony from the accident reconstruction expert that any additional modifications to the exhibit, made after the computer's first renderings, are valid.
          5. Testimony that the experts are familiar with the demonstrative exhibit.
          6. A showing that the exhibit will aid the trier of fact in understanding the expert's testimony.
          Overall it must be proven that the procedures used to feed the data into the computer were reliable and that someone checked the accuracy of the data and the computer operations.
        63 For the reasons that follow, EXPERT NAME REDACTED evidence, in light of the above, is of no assistance to me.
    We should be posting additional information in near future to this forum topic:
    • This is NOT meant as an attack on pc-crash, it is a CAUTION...
      BE SURE to double check your work!
      • This posting present examples that demonstrate that, although it is a very popular program,
        that it,
        • and other simplified momentum programs (such as virtual crash & planar impact programs),
        can be easily manipulated to get ANY results that a user may want/need/knows.
        • But it is the correct answer?
        In other words...
        BE CAREFUL! The program CAN be easily manipulated, misused and misrepresented in court cases.
        It has many times been improperly used as the sole basis for an expert opinion.
      Simulation should be used to test, refine and display an opinion...
      NOT form an opinion
    Computer programs/simulation can help understand timings, and many things unavailable to traditional analysis
    • We strongly recommend ALWAYS FIRST performing a traditional collision analysis...see 3 Day McHenry Seminars on Crash Reconstruction which includes:

      As scientists, engineers and accident reconstructionists, we should not let the unlimited possibilities of making anything look real (with animation) 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.

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