Often you are presented with expert’s reports about motor vehicle accidents. Many times, no matter what the technical issue happens to be, a diagram of the accident scene will be included. This diagram is normally generated in a CAD program ( Computer Aided Drafting ) of some kind, and is assumed to be both “ to scale “ and very precise. Litigator’s may subject the creator of the diagram to cross examination in relation to the accuracy of the diagram. Careful scrutiny of the diagram is important because the positions and measurements from which calculations of speed, time, distance and other factors, are part of the diagram and should be reviewed. If the diagram is not correct, all calculations, simulations, and animations are automatically suspect.
Crashteams experts are highly trained and equipped with state of the art laser total stations, with wich they can measure accident scenes of up to 1000 feet without the need for additional help. We measure all important points that will be used later to generate an accurate scene diagram. Important details are captured with a digital camera so you can clear the road faster.
Measuring a large accident scene >1000ft. is more complicated because it involves having to reposition the Total Station accurately so your measurement points line up.
1. Question: What type of instrument did you use to measure the scene?
Answer: Nikon, Sokkia, Leica, Topcon along with the model number
2. Question: How do you know the instrument is accurate?
Answer: I test the instrument regularly by using known reference measurements.
3. Question: When was the last time it was calibrated?
Answer: I have the instrument serviced and calibrated yearly
4. Question: Are you trained or certified to operate the instrument?
Answer: Yes, I have taken and successfully completed a forensic mapping course which encompassed the use of the measuring equipment as well as the theory of the technology, and also how to download the measurement data.
5. Question: Can you produce a record of the measurement data that you recorded on this case?
Answer: Yes, I have a complete spreadsheet of all the x,y,z coordinate data which also includes the date and time it was recorded.
6. Question: How can you convince the court that the measurements that you took at this accident scene are precise?
Answer: the instrument is capable of measuring at distances up to 2000 metres to an accuracy of 1 cm, and on this case, I took 2 reference measurements by hand with a tape measure, which I later checked using the downloaded data and found the measurements were precisely the same.
7. Question: How do we know the diagram that you have generated is to scale?
Answer: If you look at the scale bar you will see that it represents what 100 feet covers in the real world. If you then use that scale bar to measure any distance you will see that the scale bar is precisely representing that distance.
8. Question: What is the scale of the diagram?
Answer: The scale is 1: 200 ( or any other number ).
9. Question: When you downloaded the measurements to the diagram that you created, how do you know the software represents the scene accurately?
Answer: I used the software to measure between the known reference points and found the distances to be precisely the same.
1. Question: Please explain your measuring procedure.
Answer: I established a straight baseline or reference line at the scene, and then measured along the line and at 90 degrees to the line to the measurement points to establish precise x,y positions of all points.
2. Question: Did you measure the vertical position of each point?
Answer: No, this procedure only measures 2 dimensionally.
3. Question: So, your procedure assumes the scene is a flat plane?
Answer: yes, there is no way to measure vertical positions or angles by hand.
4. Question: How accurate is this procedure:
Answer: it is accurate within about 1 foot on most measurements.
5. Question: When you measure to the evidence or other points at an angle of 90 degrees from the baseline, how do you know you are really at 90 degrees?
Answer: It is estimated.
6. Question: if your measurements from the baseline are taken at an angle different than 90 degrees what is the effect in terms of accuracy?
Answer: the measurements are not accurate if that is the case.
7. Question: If your measurements are accurate only within a tolerance of 1 foot, what would be the error factor on the calculations regarding speed etc?
Answer: the range of accuracy would reflect the scene measurement accuracy.
Here is an example of a measurement log, which details each measurement point in terms of its x,y,z position as well as it’s description.
Also see how the diagram should appear which shows the measurement points, which correspond to the log.
Finally, click here to see what a proper 3D model of an accident should look like after being processed by a professional reconstructionist using state of the art measuring equipment and software.
Our Crashteams reconstructionists are the most highly trained and qualified individuals in the industry.
All Crashteams experts utilize survey equipment to produce precision crash scene diagrams and 3D models.
All Crashteams reconstructionists are qualified expert witnesses and have given testimony at all court levels and jurisdictions.
Your Crashteams experts can interview witnesses and secure detailed statements, as recorded interviews in audio and video formats.
Crashteams experts are all trained and certified as forensic animators. You will find it advantageous that your reconstructionist and animator are the same person.
Crashteams experts are qualified to use many different software applications to simulate the crash for the purposes of answering what if scenarios and exposing errors in the hypotheses advanced by oppsing experts.
You may send us reports from opposing experts and we will be able to tell you immediately if a rebuttal is useful and if so, we produce professional, objective, commentaries.
Crashteams have the expertise coverage and manpower to take on all the crash investigation requirements of a community as a public private partnership.