PC-CRASH: How Many % May An Investigator Be Wrong with pc-crash?

[MSI]

In a Crash Forum there was a posting desperate for answers which included a description of a crash in Europe or other country and included the question:

• "how many % may an investigator be wrong with pc-crash?"

• • The desperate for answers author also relayed that:
    • The police used pc crash which they said was PROOF that their daughter was coming from the right, from her lane...very slowly...
    • A second expert was hired who made a little video [impact to rest only) from pc-crash which was the same scenario as police
    • The 2nd expert never tested their daughter's version of the crash with pc-crash or other means...
    • They later found out that the 2nd expert was the regular expert from the assurance company
      In summary neither the police or the 2 experts ever tried any alternate theories of how/why the crash happened

We initially posted this to our post HELP! If YOU or someone you know has been in a crash! However a few other related questions came in so we made this also a separate thread and added additional detail:

• Note that the crash outlined by desperate for answers was a 'who's on the wrong side of the road' question and so we included an example where pc-crash was used improperly as a basis for an incorrect opinion in a case.
• This topic/response was prepared to assist anyone in event a police department or expert has used and presented PC-CRASH (or other simulation program) as PROOF of a theory...PC-CRASH is a very widely used software product however we have found that it can be easy to manipulate the results sometimes to support a preconceived opinion. Any PC-CRASH (or other simulation program) PROOF (and videos created as a result) need to be carefully examined as they might be a smokescreen.
• All crash reconstruction and simulation software products are interesting and useful products however as with ANY product users must exercise caution when using and be sure to check the veracity of any results.
• We always recommend that crash reconstruction simulation software be used to test and refine opinions which also sometimes means testing alternate theories.

The following is our response (with some additional information added to this thread) and anyone seeking an experts help in a collision may benefit from this list:

• Where are you located? Are there not any local experts who can help?
  • If you provide where you are located perhaps someone on this forum knows someone in that area.

You provided a narrative however you did not provide any evidence (pictures, diagrams, reports) on which to offer you any assistance. The following is a list of items which you should provide to allow for a proper evaluation of the crash.

• Pictures of exterior damage to the vehicles.
• Pictures of the vehicles at the scene.
• You mentioned drone pics? post those
• A police report? Any crash scene diagrams? post those
• The location of the crash? Google maps or Google Earth can be helpful in determining distances, etc.

You mentioned:

• "how many % may an investigator be wrong with pc-crash?"

Did the police or some expert in your case use pc-crash?

• if so, first the answer to that question is 'it depends'.
  • pc-crash is a momentum based simulation solution and so subject to momentum limitations and simplifying assumptions
    In several cases we have been able to make a singular change in inputs (the point and angle of momentum exchange') and change the results of a pc-crash simulation used as the basis for an opinion by an expert in a case.
    One example was a 'who's on the wrong side of the road' crash (see below)

You should obtain the inputs and the diagrams from any pc-crash simulation (or ANY computer program/simulation) used in your case.
You should also demand you get the input file in electronic form for ANY simulation/animation so you can have an expert review all inputs and rerun the simulation to verify that the inputs produce the results and then also to allow a test for sensitivities of inputs.

• A demonstration of sensitivities of momentum based solutions comes from How is Monte-Carlo method used in Accident reconstruction?:
  • Which Includes:
    • A classic example of problems with the sensitivity of a linear momentum solution is when it is applied to a t-bone type collision.
  What that ‘classic’ example is meant to illustrate is that when applying a Linear Momentum solution procedure to ANY accident you need to test sensitivities of inputs (angles at impact and angles at separation). If a small change in an angle makes a dramatic change in the results then obviously you need to focus on defining and refining the inputs as well as consider using a more sophisticated solution procedure (like a SMAC simulation).
  
  All simulation inputs for pc-crash may not be included in a printed run summary.
  • In most courts in the USA the inputs for any simulation or animation must be provided in electronic form.
    This allows the other side to rerun the simulation to be sure all inputs are produced so they can be checked
    • weights? specifications? tire properties? values for friction? friction zones? terrain slopes? source of terrain information?
      • Today with cloud scanning of scenes a reconstruction (by Leica, Trimble and/or Faro) can include gigabytes of information about the crash scene and vehicles which are NOT included in any printout (or is they are it will be thousands of pages of unintelligible numbers)...not quite full disclosure of inputs. again WHY full input file in electronic form MUST be required.
    • Proper dimensions for evidence location and ability to compare that to the simulation/animation?
    • if animation, is the animation physically possible and does it obey Newton's Laws?
      • the electronic inputs provide a list of the positions and orientations for each frame so the speeds, speed changes, and approx accelerations can be calculated
    • And do the graphics/video created match the inputs provided?
      • we have cases where inputs (in paper form) and graphics/video provided looked OK however once we obtained in electronic form we found that the printed paper inputs were different than the electronic inputs and did NOT produce the same results/video/graphics!
  Here are some links with additional information:
  • HELP! If YOU or someone you know has been in a crash!
  • What files should be produced for Simulation and Animation
  EXAMPLE: Here is a comparison of two pc-crash runs in a case.
  • An expert used pc-crash as the basis for his expert opinion of who was on the wrong side of the road.
    Once we obtained the electronic pc-crash inputs, we moved the impact point of the vehicles and changed the arbitrary and subjective 'point of momentum exchange' and also 'matched the evidence' (see below)
    We demonstrated that either scenario could be proven with pc-crash.
    So what to do?
    We then tested the experts 'proof' by setting up and running the crash with msmac which produced very different results for the two scenarios. Since with SMAC the solution includes the trajectory and damage produced by a given impact configuration and speeds.
    • msmac is like running a mathematical full scale test since it models the collision forces for each millisecond the vehicles structures interact (100-150 milliseconds) instead of trying to approximate the results of a collision interaction with an "instantaneous exchange of momentum" at an "arbitrary point of momentum exchange"
      • With msmac you set up the mathematical full scale test, set the speeds and then hands off run (simulate) the vehicles into each other. It calculates the movements of the vehicles and displays the structural damage that occurs from the impact speed, relative locations, movements of the vehicles and relative crush stiffnesses (it calculates the vehicle trajectories and collision forces for each and every millisecond!).
      • With pc-crash you must pick a 'point of maximum engagement'' and move the vehicles to that position with no feedback or verification as to whether the speeds, relative locations and collision interaction of the vehicles will produce damage which in any way matches the amount and location of the actual damage. The collision forces are not calculated.
    • We say pc-crash as an arbitrary and subjective 'point of maximum engagement and angle of contact plane' because the pc-crash input guidelines and training videos require the user to subjectively position the 'point of maximum engagement"
      As the pc-crash user moves the point and angle around the user can watch the speed results change until an arbitrary and subjective position and angle is found which produces the desired or known results. Note: there is an 'auto calc' option on their crash simulation dialog however there is no indication if it has been used. In every case we have been asked to evaluate a pc-crash reconstruction it has NOT been selected and selecting it and rerunning the collision dramatically changed the results.
  Pc-crash, and other momentum or planar impact based collision programs, can be easily manipulated. So be sure to test and check any simulations which form the basis for conclusions.
  And of course test and check ANY reconstruction, simulation or animation program results.
  
  
  The experts pc-crash reconstruction which "proved" a vehicle on the wrong side of the road was as follows:

  

  wrong side 2.png (464.91 KiB) Viewed 4780 times

  However we then with pc-crash put the vehicle in its proper lane and made a minor change to the arbitrary and subjective pc-crash 'point of momentum exchange which then also "proved" that the vehicle was in its proper lane!!

  

  wrong side 1.png (530.54 KiB) Viewed 4780 times

  MAIN POINT: Pc-crash, and other simplified momentum based collision programs, can be easily manipulated. Be sure to test and check any conclusions based on momentum based programs or equations. Test and check ANY and ALL reconstruction results.
  

[MSI]

In doing another reread of the narrative posted in the other forum and some additional pictures the author of the original post added (some posted below), the following are some comments:

• "the other woman was driving on the wrong side and tried to correct to her side and the other driver on the right lane, tried to dodge, so the debris ended on the other lane and the driver who was riding on the wrong side and tried to correct was responsible..."

i am reminded of a driving story told to me by my late uncle Ken as a warning when driving...

One of his first driving experiences some 75+ years ago (he passed recently at 90+ years old)
As a young driver he was driving down the road in rural Maine and saw a vehicle on his side of the road.
He decided to go to the other lane to pass the vehicle on the wrong side of the road.
The other driver at the last minute came back over to his proper lane of travel and they collided.
The police charged my uncle with being on the wrong side of the road and causing the crash.

The police can only go by 'where is the evidence' although the other driver was the 'town drunk' and drunk at the time (this was in rural Maine)
Studies have shown that intoxicated people head 'towards the light' so that is why trying to swerve around someone traveling in your lane may make them come back 'to the light' and collide with you and make it appear you are to blame.
it is also why at some crash sites all lit up with emergency vehicles that they sometimes 'attract' intoxicated drivers who 'head towards the light' and crash into the rescue vehicles and cause further carnage.

The main point of this is that the police depend on the evidence and if all the evidence shows a collision in one lane, the person in the wrong lane is charged as your daughter was charged.

Why didn't the police download the EDRs in each vehicle?

• you haven't indicated the make/model/year of each vehicle to determine if the vehicles had any information.
• Some EDRs have information for 5 seconds prior to the crash.
• As a minimum why didn't the expert your insurance company hire read the EDR on your daughters vehicle since it is an easy process

You have not uploaded all photos. In your narrative you mention pictures with police cars, etc
see link above for secure place to upload them.
And also if you have them, please send the pc-crash inputs and report and animation and any police and expert reports.
Notes on the scenario that you mention:

• NOTE: Your scenario puts the white vehicle in the wrong lane but helps explain a possible reason why.
  • The other vehicle was in your daughter's lane and so she swerved left. They crashed in the other vehicles lane the local law may make it your daughters fault even if you can prove the swerve left by your daughter was due to the other driver.
  As a quick demonstration, i did a msmac3D simulation of two somewhat similar vehicles on the scene w/pc-crash results you posted earlier in this thread
  In this quick preliminary demonstration i demonstrate if the other vehicle came back from the opposite lane you still can match the approximate rest positions of the vehicles
  • pc-crash includes a MAJOR simplifying assumption of an "instantaneous exchange of momentum" during a crash which relies on a user set arbitrary and subjective "point of maximum engagement".
    • Other programs which include this simplifying assumption are virtual-crash and planar impact models
    • These types of programs make getting the results you want and need easy by a judicious choice of "Point of instantaneous momentum exchange", but are the results scientifically sound and correct?
    • Do the speeds and orientations of the subject vehicle "AT IMPACT" produce a match of the "point of momentum exchange" AND a correlation of the damage?
    • Having a simulation program which included the modeling of the damage forces and moments during the crash provides an answer to that addition KEY question.
    • Actual crashes occur over 100-200 milliseconds with forces and moments acting along and during the entire crush interface/interaction
  • If we were able to obtain the police/others pc-crash inputs (.PRO file and/or printed outputs) we probably could demonstrate that this scenario can also be "proven" with pc-crash by using a different arbitrary and subjective "point of maximum engagement"
  • With msmac3D simulation you actually mathematically crash the vehicles into one another including calculating the forces and moments of the crush interface and interaction for every millisecond during the 100-200 millisecond crush interaction.
  The video below simply demonstrates the evidence might be matched in either scenario
  To decide which fits best one must do a thorough examination of ALL he evidence as it might reveal which scenario best matches ALL the evidence.
  • EVIDENCE/DATA REQUIRED IF AVAILABLE:
    • The weights, make/model/years, scene information,
    • Damage photos/estimates/areas on each vehicle, extents
    • scene photos and measurements, EDR outputs, etc.
    • MAIN POINT: An expert cannot simply state that pc-crash 'proved' a single scenario without examining the other possible scenario and/or using a simulation program which Models the crushing of the vehicles and damage interaction to see if the two scenarios might allow determining which scenario best matches the evidence.
    • Adding the EDR data to the puzzle might also help clarify which vehicle did what in the 5 secs of pre-impact (if available)
    • • if EDR data was available (make/model/year) from either/both vehicles it begs the question: WHY didn't the police read the EDR data?
  THE VIDEO BELOW IT IS A QUICK PRELIMINARY DEMONSTRATION!
  • NOTE: This also still puts the white vehicle in the wrong lane but helps explain a possible reason why.
    • the other vehicle in the white vehicle's lane and so the white vehicle swerved left and they crashed in the other vehicles lane the local law may make it your daughters fault even if you can prove the swerve left by your daughter was due to the other driver.
    This is merely as a demonstration that the other vehicle might have been coming back into its proper lane.
    • (need actual makes/models/weights, damage measurements/pictures, tire mark evidence, scene evidence, etc)

    

    POI v POR msmac3D.jpg (238.16 KiB) Viewed 4579 times

    here are a few of the pictures also posted:

    

    pdf photo received from the newspaper.jpg (21.6 KiB) Viewed 4597 times

    

    photo expert defense.jpg (28.97 KiB) Viewed 4597 times

    

    photo expert defense2.jpg (28 KiB) Viewed 4597 times

[MSI]

July 2020: moved entire response from topic HELP! If YOU or someone you know has been in a crash! to this topic
to reduce having to duplicate any refinement, etc also add some introductory sentences also above:

• This topic/response was prepared to assist anyone in event a police department or expert has used and presented PC-CRASH as PROOF of a theory...It is a very popular software product however it is easy to use and some use it to manipulate answers to support a preconceived opinion and so any PC-CRASH PROOF (and pretty pictures and videos) might be a smokescreen.
• It and all crash reconstruction software products are interesting and useful product however as with ANY product users must exercise caution when using and be sure to check the veracity of any results.
• We always recommend that crash reconstruction simulation software be used to test and refine opinions which also sometimes means testing alternate theories.

[MSI]

A response was posted to the other forum with additional questions and information on the crash.
Please see the latest post on the other forum.

RESPONSE
I am sorry for the issues you are having and hope your children have a full recovery after this most difficult time.
In your description you include a lot of accusations about missed or faked evidence and other things

• for example the light coming on you say to blind you, thinking differently: what it they were actually trying to light up the scene for you to take pictures?

Obviously some or none or all of what you say and think think may be true.
Crash reconstruction relies on facts and evidence!
Your attorney should let you know about the local laws since if your daughter swerved at the last moment to the other side to avoid a crash in her lane while at the same time the other driver swerved from the wrong lane but returned to their lane of travel at the time of impact, your daughter may be responsible even if you prove she was swerving to avoid the crash.
It depends on the local laws and whether you can definitively prove that the police assumption is incorrect.
Main point is that to prove things will require a lot of time, effort and money on your part and may not result in justice being served.

If you'd like someone to review your crash on this forum in more detail, you need to post up or send all the photos since you mention a lot of photos:
You said in this latest post:

1. we managed to take 2 pictures, and you can see that 4 policemen are standing in the middle of the roads where oil and scratches are..
2. there was a picture taken of the speed of our daughter but not of the other driver..
3. pictures by the police
4. the investigator took 8 pictures in 2 minutes with his hand camera,he took 11 pictures of the other car, but not of the roof, not of the rear end, 1 picture of the outside of the car of our daughter
5. drone pictures...he took 21 pictures in 4 minutes...bad light...

Please post up the photos or send them.

Did police make any measurements of final resting positions? A scaled scene diagram?
Have you asked for the actual pc-crash input files used by police and then by the investigator you described in a prior post who also did a pc-crash simulation for you?

Most of the questions you have posted up are things your local investigator/reconstructionist should have been able to answer and consider.

A couple responses to minor points you said:

• "Both cars were the roofs damaged"
  • The roof damage was probably post impact extraction of the passengers from the vehicle. They cut the pillars and peel back the top to get easy access to injured parties. The roof damage probably had nothing to do with the crash.
  2) "On our first picture you can see in the middle, on both lanes a "white powder", I read somewhere this is like "dust" from the brakes, but can't find it again"
  • I doubt brake dust. Brake dust is normally brown or gray (heat of brakes cooks any dust), and not white. Police or fire departments in response to the crash spray sometimes foam or other material to cover any gas or other possible flammable materials from the vehicles.
    That is probably what you see
• "The police just once mentioned the truth: both cars were damaged all around"
  • From the pictures you have sent the main damage related to the crash was to the fronts of each vehicle.
    There most likely was no sideslap damage or any other areas of the vehicle that might have been damaged after the primary impact.
    Debris scratches are not considered crash damage for the purposes of crash reconstruction.
    You mentioned trees: A diagram with the location of the trees relative to the positions of rest of the vehicles is required to see if either vehicle with what might be tree induced damage might have been in proximity to the trees.

The main point of this response is to let you know that sometimes you need to simply accept the situation and move on.
If the police were actually out to cover up the cause of this crash then you will have a very difficult time proving otherwise.

If your daughter swerved to the improper lane to avoid a collision with a vehicle in her lane and that vehicle also swerved such that all the debris and impact were in the opposing lane, then you may be limited by local laws and/or limitation of the documentation of the crash to prove your case.

Unfortunately sometimes it is extremely difficult to conclusively prove your scenario with the limitation of the evidence you have.

I am sorry for the issue you are having.

[MSI]

You uploaded a lot of information to our technical support dropbox (>280 pictures, etc)
we will try to go through the information in the next few weeks or sooner.
we noticed some photos and descriptions are photos of pages from reports: police reports and/or investigator reports.
Could you also upload the police report and any other reports.
we can translate and we will keep the contents confidential
Any and all of your lawyers should have requested and received any and all reports.

• The police include it in their report, and
• you mentioned one of your investigators
  both relied on pc-crash to come to their conclusions or support their conclusions

You must be provided a copy of the pc-crash input files otherwise it should NOT have been accepted by the courts since you must be allowed a proper review of ALL reports, measurements, and for simulations or analyses the inputs to be sure any and all conclusions drawn from the pc-crash or other analyses are of sound scientific basis.

• We have noted in this forum topic and others where we have found extreme sensitivity of pc-crash and an easy ability to change the conclusions, particularly in 'wrong side of road' type crash reconstructions (presented earlier in this post).

It is IMPORTANT to be able to obtain and evaluate their pc-crash inputs in printed and native form (pc-crash input files have the PRO file suffix)
The pc-crash inputs files can be large files depending on the graphics (what type of scan they used at the scene, etc)
for additional information please see:

• What files should be produced for Simulation and Animation

[MSI]

On the other forum an additional response was posted about the case wherein the police used pc-crash to "prove" who was on the wrong side of the road.
Our response:
I am sorry for the many issues.
I think it is time to use email for further questions/details/etc and to expedite responses. Please see link below to our contact information.
You need to ask your lawyer:

• WHY have they not obtained the police report and/or the report with the color pictures, etc you've posted parts of in this forum?
• WHY have they not obtained the pc-crash simulation(s) by police and/or investigators '
  • As i have posted in PC-CRASH: How Many % May An Investigator Be Wrong with pc-crash?
    In many collision configurations pc-crash is extremely sensitive to minor changes in certain inputs such that a single change and demonstrate that their proof' is not a proof! Since a change to the subjective and arbitrary "point and angle" of maximum engagement required for the programs to exchange momentum in an single instant is easy to manipulate to get the results you want, particularly in a 'wrong side of roadway' type crash.

And last i would suggest having a search of the junk yards in your area

• In several cases we have been involved in lawyers/investigators were able to find a junked car and then read the EDR.
  You should have a local expert find one or both of the cars and see if EDR data available.

THAT would answer a lot of the questions (depending on model year of the vehicles, etc a LOT of information may be available)

Please use this link for contact information and either you or your lawyer please send us an email so we can see if we can be of any additional assistance in your case.
Contact Information

[MSI]

As part of another thread about Simulation Analysis: Effects of Input Variations we summarized issues with Instantaneous Exchange Momentum Simulation Programs like PC-CRASH, Virtual Crash, Planar Impact Models, and others:

• Simplified momentum equations and programs require the user to pick a point and angle/direction to instantaneously exchange the momentum of a vehicular crash.
  Any vehicular crash takes 50-150 milliseconds (or more) for the collision interaction which these programs/equations consider a SINGLE 'instant'.
  When applying a momentum solution it is subjective and random HOW a user sets the LOCATION and the ANGLE/DIRECTION for the INSTANT of the momentum to be "instantaneously exchanged"
  
  Please see
  • The Major Shortcoming of Simplified Momentum Simulation and Analysis