Crashteams collision reconstruction experts are often called upon to assess the forces involved in collisions where there is little visible damage to the involved vehicles. The reason we are assigned to these cases is simply that there is a suspicion that there was insufficient force in the collision to generate the injury causing mechanism. Normally the orientation of the collision is a same direction rear ender. Normally, the party advancing a claim for injury is in the struck vehicle. The technical process of determining the magnitude of the collision involves inspection of the involved vehicles. We inspect the bumper surfaces for signs of permanent deformation. We inspect, if the vehicles are so equipped, the bumper isolators for signs of sudden compression.

Many times, the involved vehicles have an impact absorbing rear bumper system.  This is a polystyrene filled, polyurethane covered rear bumper.  The rear bumper is supported by a steel reinforcing bar that is rigidly mounted by brackets to the unibody frame of the vehicle.

Research has shown that bumper isolators, which are fluid and gas filled shock absorbers designed to prevent vehicle damage from collisions with barriers or other vehicles, can set the threshold of visible vehicular damage at delta Vs ( speed changes ) ranging from 8.1 to 12.4 mph in modern cars. Yet below this threshold, the occupant can be exposed to significant acceleration pulses. The reported threshold for soft tissue injury of the neck in healthy adult males is a (vehicle) delta V of 5 mph. Therefore, modern passenger vehicles can crash at nearly twice this injury threshold, yet appear undamaged. Similar effects are seen in cars equipped with polystyrene and polyurethane impact absorbing bumpers. Lower speed collisions result in less plastic deformation of colliding vehicles.  In these relatively elastic impacts a greater proportion of force is directed to the occupants. There is no scientific evidence that these bumper designs have reduced injury to occupants.

It is possible for the bumper surface on the striking or struck vehicle to reveal little signs of contact as it is designed to reassert itself and have minimal repair costs on impacts of 5 mph and less. The SAE technical paper entitled “Automobile Bumper Behaviour in Low Speed Impacts” reported on impact testing which indicated vehicles with the polystyrene filled, polyurethane covered rear bumpers, would sustain impact speed changes up to 13.7 kph without any sign of permanent deformation.  On the other hand, poorly designed bumper systems can allow thousands of dollars in damage to occur at speeds less than the generally accepted injury causing threshold.

The problem is now that the involved vehicles may have undergone impacts of a magnitude greater than the injury causing threshold. Impact testing with human volunteers done in British Columbia has shown that the first signs or symptoms of a neck injury begin to appear at a collision magnitude of 6.5 kph ( speed change).

An SAE paper entitled “Analysis of Human Test Subjects Kinematic Responses to Low Velocity Rear Impacts” by McConnell indicates that even before the neck is hyperextended, the injury mechanism begins to occur.  This means before the head accelerates any great distance rearwards to the point where the rearward excursion is limited by the positioning of the head rest, the injury has already begun. However, the injury mechanism does not stop there.

For example, if we were to assume the struck vehicle did sustain a speed change of 14 kph, this would generate 2.6 – 4 g of acceleration. This is based on an impulse duration of 100 – 150 milliseconds. The vehicle would be projected several feet forward and the consequence for the occupant is his body would accelerate at the same rate as the vehicle in the places where his body is supported by the vehicle seat. In this case, his neck would act as a lever and create a higher rate of acceleration for his head, because it is not supported. It has been reported the relationship between the head acceleration and the vehicle acceleration is 2.5:1. This means the acceleration forces would be 6.5 – 9 g., acting at his head.

In summary, the issue of whether or not the impact forces were sufficient to generate a neck or back injury is difficult to assess when the involved vehicles are equipped with modern bumper protection systems.

What can Crashteams experts do for you?
We can examine the available material on a preliminary basis to determine if the available data is sufficient for one of our experts to generate a quantitative analysis, answering the primary question of “ were the forces sufficient to generate an injury “. For this process, we will not charge you a fee.

References:

“Repeated Low Speed Impacts with Utility Vehicles and Humans,” G.P. Neilson, G.P. Gough, Little, West and Baker, Accident Reconstruction Journal, Volume 8, #5, September/October 1996.

“Data and Methods for Estimating the Severity of Minor Impacts,” Bailey et al, SAE950352

“Clinical Response of Human Subjects to Rear-End Automobile Collisions” J. Brault, Wheeler, Gunter, Brault Arch Phys Med. Rehab Vol. 79, Jan 1998

If you are interested in accident reconstruction services please visit: 
www.crashteams.com or call us at (877) 372-3728

In addition to the legal requirements, any expert worth his salt should have the “show the work“ documents. In other words, there should be electronic or hand calculations to show how the answer was achieved. Keep in mind, most experts are either taught to use a series of equations, already derived, for application on different cases ( police trained ), or trained to derive the applicable equations from first principles ( engineer reconstructionists). Regardless of background training they should explain the equation they used, why it was used, and where it came from. If an expert accident reconstructionist cannot do that, he/she is obviously not an expert.

I am sure by now that most of us have viewed the youtube video(Accident Reconstruction Expert) which shows an effective and embarrassing cross examination of a so-called expert. Under cross, he was asked to convert feet and inches to feet and decimal feet. He refused to do so without consulting his equation sheet. What he was asked to do is, at best, Grade 6 math and clearly he was not capable. Triumphant was the relentless manner of the attorney who realizing the weakness in math skills, persisted until the court was convinced of the incompetence of the witness.

All reconstruction experts, regardless of background training, should not require a “ list “ of pre-derived equations and formulae. As experts they all should be capable of deriving almost all equations. There are some very intricate equations used for calculation tractor trailer rollover thresholds that are too complex to expect anyone to derive during a cross examination.

All reconstruction experts should be able to explain the theory behind any mathematical approach to solving basic issues of velocity, acceleration, time, and distance. Often attorneys do not delve deep enough into the questioning for fear of simply making the expert look more competent, but properly worded, those types of questions will often reveal a basic lack of understanding.

Unfortunately, many reconstruction training schools teach students how to choose the correct equation, and how to apply it, but fail to teach the derivation or supporting theory of its application.

Attorneys should ask more technical questions of experts relating to crash reconstructionists, with the guidance of other reconstructionists. Then the answer is known for each question, and the attorney can persist until the expert answers or fails to answer. Once the proper questions are known, the next level of questioning can occur, which is asking the expert to re-calculate answers using a broader range of input variables, such as roadway friction, vehicle stiffness values, and many other values and assumptions which can illustrate a much broader range of proper answers.

How can you better prepare to cross exam an expert witness in accident reconstruction? Simply call another expert and explain you need support on creating an effective set of questions for cross examination.

What can a Crashteams Professional do for you regarding cross examination?

Crashteams experts will prepare a powerful set of questions, provide you with the correct answers, to assist you in exposing the weakest side of your opponents case.

For more information, please do not hesistate to call any of our Crashteams experts. We can help!

To find out more on how your Crashteams partner can help you please go to:www.crashteams.com
or call: (877) 372-3728

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.

You must find out how the diagram was created. Was it generated from a proper survey of the site, or hand measurements, or simply an artist’s rendition? Any diagram generated from any process other than a proper forensic mapping procedure would not be acceptable in terms of accuracy. Forensic mapping means using a total station to precisely measure each point representing the scene geometry, accident evidence, and vehicles.

Cross Examination of Total Station measurement procedure

If it was generated from a proper survey ( forensic mapping ) , which downloaded to a scale diagram, then the following more sophisticated questions should be posed. Here are some of the questions, and of course, the answers that should come back.

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.

Cross Examination of hand measurement procedure

If the measurements were generated from hand measuring, which resulted in a diagram then the following series of questions may be included in the cross examination.

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.

Measurement Logs

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.

See a Sample Measurement Log

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.

When hiring a reconstruction expert to record and preserve an accident scene, make sure he not only has the proper equipment; but also is qualified to use the equipment.

To find out more on how your Crashteams partner can help you with taking scene measurements / forensic mapping for crash reconstructions please go to:www.crashteams.com
or call: (877) 372-3731

The application of animation technology to motor vehicle cases has been going on for about 20 years and in that time we have come a long way.

Then…

The folks that created the animations and delivered them on VHS tapes were almost always specialists in the field of animation as opposed to accident reconstruction professionals. The process was arduous and expensive. The challenge was to represent the opinion evidence of the reconstruction professional in the form of a 3D animation. That meant considerable time was expended between the reconstructionist and the animator to ensure the moving objects were in the right positions at the precisely correct point in time. The reconstructionist had to provide spreadsheets of time vs positional data which was ultimately transformed into a movie which ran for a few seconds and cost $10,000 and more. Often months were spent getting it right through a process of reviewing several draft movies. The end result was vulnerable to rejection by courts since the animator was not the reconstructionist and often factual evidence and reconstruction calculation evidence could not be produced to properly found the basis of the animation. Lawyers would typically have to call both experts to trial.

Now…

Animations are now created by the same experts that produce the reconstruction reports. Thanks to modern, intuitive computer software a highly trained reconstructionist ( all Crashteams partners ) can produce a 3D animation of their opinion relating to vehicle velocities, and time distance positioning. The animation will be in real time, and cost a fraction of what was charged in past years.

What should you expect?

Expect the delivery of a high quality, 3D animation within a few days of the production of the final reconstruction report. In fact, your reconstruction professional can send you a draft movie in .wmv or .avi format as an email attachment for review. You may wish to have several views to make the point.

You should also expect the animation to run on a precisely accurate 3D model of the crash scene and the models in the scene should be precise models. All information depicted will be subject to extreme scrutiny due to its potential to persuade viewers, so it must past muster in all respects.

Getting accepted..

We cannot comment on all the legal requirements for the acceptance of animation evidence in all jurisdictions, however, in terms of the features of the animation that may be examined for accuracy we can offer solid advice. Your animation movie, must be founded on facts. The actual scene measurements completed with total station electronic measuring equipment is the best. The scene on which the animated vehicles move must be proven to be accurate. The time, distances, and velocities must have been determined by accepted calculations and the report that summarizes the dynamics that are viewed in the animation must be also accepted. A special animation report is very helpful. All Crashteams partners provide Animation reports with their animations to assist you in getting the animation accepted. This report outlines, every 5/100ths of a second, the time, position ( x,y,z ), and velocity of each moving vehicle or other object.

It is also very helpful to have time, position, velocity information being displayed in real time as the animation plays. Finally, the animation should run in real time. In other words, the time displayed in the animation should be the same as on any external timer so that no challenge to accuracy will be produced.

See a sample animation

Imagine that within a couple of days you can view an animation like the one above.

Click on this link to read some interesting legal precedents about the acceptance of animations
http://www.mclane.com/newsroom/articles/litigation/animation.php

To find out more on how your Crashteams partner can help you with animations for crash reconstructions please go to: www.crashteams.com
or call: (877) 372-3731

Crashteams Inc. and Forensic Dynamics Inc. have collaborated on supplying technical assistance to a new National Geographic Series called Survival 360. Survival 360 takes a 360 degree look at the science of surviving an extreme disaster. With this novel approach, the series will retell amazing stories of survival using original footage and will uncover the hard and fast science behind some of the most amazing survival stories of our time. At the center of each one-hour episode is a harrowing and personal story of survival-against-all-odds.

Filming of the first episode began in Dayton OH last week. Crashteams Inc. CEO, Tim Leggett, was the Lead Investigator, and Forensic Dynamics Inc. Animator, Ryan Leggett, supplied animation services. Crashteams SOUTHERN OHIO supplied on-scene investigation equipment and support personnel.

This new investigation by Investigator Leggett results in a startling new finding of this 8-year old case involving a pedestrian’s escape from death. This episode will air in the Spring of 2011. Stay tuned!

Crashteams is pleased to announce that Charan Mellor has joined Crashteams CALIFORNIA and will be servicing the Greater Los Angeles area. We wish Charan well in his new position with Crashteams.