Why are Accident Engineering Reports Incomplete And/ Or Misleading?

By: Patrick Sundby, Accident Investigator

Specializing in Low Speed and Catastrophic Crashes

 

From my experience as an accident engineer, there are several reasons engineering and accident reconstruction reports are problematic.  Let’s address the first and biggest issue, cost.  Many attorneys don’t realize the true value of cases because they deal with doctors who often doesn’t know how to document the patient’s injuries properly, then there are the Colossus issues that most also do not handle in their documentation.  This is a huge advantage to the insurance company who have banked on the sloppiness and ignorance of the entire medical-legal community.  However, there is a growing number of doctors and attorneys who do know.  If you’re reading this and should follow Dr. Mark Studin teachings, you have an advantage over most of the industry as you also know how those insurance algorithms are used to devalue a case and how documentation on your part as a doctor is critical in refuting it.

In this sense, the insurance company knows they will pay, a majority of the time, a minimal amount for a collision even if the case should have a much higher value due to the nature of the injuries.  The insurance companies know this for several reasons, but the biggest reason is cost, not for them but you.

For the sake of discussion let’s say the average case settles for $15,000.  If the collision specialist costs $2,000 to $5,000 (in addition to the doctors and the other specialists), this is an expense which cannot or chooses not to be absorbed by solo attorney’s, smaller and even larger legal firms. The insurance company knows this and use it whenever it presents itself.

Why can a “deep pocketed” insurance company afford to pay a specialist on a smaller case?  There are few reasons but the two biggest are the insurance companies can absorb the cost of a smaller cases AND the consultants will do the work, in some cases, pro bono, as good faith towards the client to get more cases.

Obviously, if the attorney cannot make any money they will not take the case and paying for a collision professional is a significant factor in this decision, especially if the defense already has one.  If you, the doctor, are also the collision expert, this greatly reduces the attorney’s costs per case while making you more valuable as a resource AND affords the attorney the opportunity to take on more cases.

The cost concerns lead to a second problem, identifying inaccuracies.  I have yet to meet an accident engineering defense specialist who will explain the shortfall of a case because it will expose their inaccuracies and will not bode well for them regarding future referrals. MANY low speed collisions have gaps which must be filled in with vetted data and very carefully chosen.  The use of generalized data (which is the norm in the industry to use) is very dangerous as it makes the gap for results reliability too wide. The results will have too much margin for error and that margin of error is often the difference between prevailing or being on the losing side and all too often accepted as accurate, but is not.

Consider the following screen graphic:

In this section we discuss why time is a critical factor.  In the picture above, we illustrate a train, which collides with a barrier at 100 miles per hour and crushes.  The associated math demonstrates how increasing the time decreases acceleration (see circled numbers).  In this example, there is no room for doubt regarding injury as its speed and acceleration is well beyond accepted thresholds.  What if we change the speeds so they are very close to those injury thresholds?

Consider the second example, here the speed of the train represents final approach to a stop barrier where the engineer is a little careless and bumps the stop barrier.  What is important to note about this visual is the time.  If we double the time (from .05 to .1) the final g force is halved (resulting in 2.267 g’s). What if there were studies we could cite which say the time needed for a train to final stop is .075 seconds?  The first time value of .05 would be too short, the second value of .1 would be too big, and both don’t fit the cited studies.

In this example the time variable changes a very small amount but the resulting change in the g forces may no longer be enough to substantiate a claim for injury.  This is why the justification for any values assigned is so important.  If you don’t know why the variables are there and why or how they were chosen, they you don’t know if they are accurate or not. A small deviation is often the arbiter for success or failure in a case in determining if there were sufficient transference of forces required for bodily injury.

Cost and inaccuracies are two of the problems commonly faced by attorneys regarding collision reconstruction. For doctors, there is now a recognized course [CLICK HERE] to give you the training to be an accident engineer/reconstructionist and for the lawyer, when there is a defense engineer, you MUST have someone dissecting the math to ensure accuracy because usually the “guestimates” used will work against you in settlement or litigation. 

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Accident Scenes & Police Reports

By: Patrick Sundby, Accident Investigator

Specializing in Low Speed and Catastrophic Crashes

 

There is a myriad of questions which centered around accident scenes and police reports.  We will address why reports exist, how conclusions are made, and what you should take away from a report and the role of the police officer as an investigator. This topic can be broken down into a lot of different categories; here we will focus on general reporting and collision analysis.

Why do police take general reports?  The most brutal answer is because no one will remember the details in two days, much less two years and they will argue it constantly; but it’s also because society needs a third party who should be an impartial fact evaluator.  “Should” is emphasized, but we need to describe what an impartial evaluator of fact is in the context of this writing.  Within this definition we are assuming the officer / deputy has sufficient training to determine what evidence plays into the case.  Imagine if you went to a call for domestic assault between a husband and wife.  Upon arrival the wife tells you the husband is using drugs and sexually assaulting a young child.  When you question the husband he denies the claim and has the wife’s prescription bottle in his hand – the medication’s listed side effect is “hallucinations”.  This is important relevant evidence the law enforcement officer should weigh in his or her decision. 

We are also going to assume the officer / deputy has no bias or stereotype towards the parties involved OR they do but recognize it and adjust accordingly.  Imagine if the officer from above is female and just went through a difficult divorce.  Does her personal life have an impact on believing the husband?  If it does, what does should she do about it?

Police write collision reports for the state (in which they operate) departments of transportation.  The report is designed to collect information regarding roadway design, operator error, alcohol and /or drug use, etc.  While important, one of the last concerns is for the report to document for the parties involved the specifics of the event.

With utilizing report templates, experience, training, and bias can significantly affect collision reports.  Why?

There are many reasons police have errors in their reports, but by far, the main reason is lack of training.  In order to make a police officer, candidates attend an academy which averages six months, some are longer.  Typically, collision investigation for basic recruit training is less than a day’s worth of training.  In this time the instructor needs to cover everything from scene security to traffic patterns to general hazards.  Most training doesn’t include: skid mark interpretation, speed calculations, principle direction of force, drag factors, etc.  In fact, unless the student after graduation and long into his or her career chooses to attend further training there will be no updates, refreshers, revisions, or continuations to the academy foundation.

Specialty training is necessary to understand the concepts and the physics behind a motor vehicle collision and these are not part of the basic academy curriculum. Therefore, when determining causality and/or specifics of the accident it is critical to ascertain the extent of training of the police officer.

To address the last point, what you should take away from a collision report, we will discuss a real case brought to me by one of you.

A while back I was contacted by a doctor, his family member was involved in a collision where she was rear ended by a truck in heavy traffic; twice.  The family member told the investigating officer their vehicle was established in a lane of travel with the truck behind it.  The truck then struck the vehicle while in traffic twice.  The truck driver told the investigating officer he didn’t know where the vehicle he struck was, but he was coming onto the highway via an “on ramp” and thought the vehicle attempted to pass him in the shoulder and cut in front of him which is why he struck it.

The investigating officer acknowledged there were no marks in the roadway to establish where the event occurred but he did write the report in favor of the truck driver. When I inquired about his reasoning and his background he informed me:

“I wrote the report in favor of the truck driver based on the damage to the vehicles although I had no formal training on damage interpretation and event correlation and could not establish through evidence, where the vehicles were in the lanes of travel.” While the gut reaction is to blame the officer, in this case the municipality who employs him is the root problem.  This agency has failed to train the officer and provide him guidelines to work within.

All that can be taken away from the crash itself is the truck rear ended the vehicle and it likely occurred as the vehicle driver described where the truck driver admitted not knowing where the vehicle was to begin with.

So what do you take away from a police collision report?  Only those facts which can be verified by witness, corroborated evidence, or soundly concluded by the two. The police are fact gatherers, not “causality arbiters” and should be utilized as such. The caveat is there are police experts who have advanced training in accident investigation, crash dynamics and accident reconstruction. My training lends me to be expert in all of those fields, but the average police officer is not and should not be considered as one.

Patrick Sundby has decades of experience in the automotive industry including several years in law enforcement collision investigation. He has also been a driver training and firearms instructor in law enforcement and a police officer for 9 years before specializing in accident investigations. He has had the privilege of participating in both learning and teaching at Prince William County Criminal Justice Training Academy in Virginia and studied at the Federal Law Enforcement Training Center in Georgia. His specialty is low speed and catastrophic crashes and has testified over 500 times at various level. He can be reached at 571-265-8076 orThis email address is being protected from spambots. You need JavaScript enabled to view it.

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Crash Dynamics and Accident Reconstruction Q & A's

By: Patrick Sundby, Accident Investigator

Specializing in Low Speed and Catastrophic Crashes

 

1. “How do airbags work and why do they deploy in some cases and not others.”

Almost all airbag equipped vehicles contain an airbag control module.  The module monitors various vehicle systems and has a predetermined threshold for deployment; in simpler terms, this means the collision has to meet certain settings to deploy an airbag.  While each car brand’s system is specifically different from the next the concept is the same.

The module constantly monitors a vehicles speed and when a collision occurs the module can tell the change in speed is happening faster than if the car was slowing by brakes alone.  IF the collision, as calculated by the module, is extreme enough it will deploy the appropriate airbag(s).  The module has the final say in why an airbag is deployed, this is truly vehicle specific as well as module software & hardware dependent.

The module can knows, via onboard accelerometers, of changes in the vehicles direction and speed.  The module constantly calculates these changes and when it “sees” a change beyond preset thresholds it begins to monitor, very closely, the changes (this is called algorithm enablement).  If it determines the changes meet the criteria for airbag deployment it will deploy the appropriate airbag(s).

Many vehicles also have failsafe sensors mounted in the vehicle which are designed as a secondary mechanical and/or electrical triggering system.  These sensors are mounted on the front of the vehicle, usually under the radiator, when crushed or damaged they force an airbag deployment.    

Occasionally, someone will ask if how a vehicle knows if a seat is occupied.  The driver’s seat is obvious, beyond this, the front passenger seat has a pressure sensor in it which can tell when a predetermined amount of weight is on it, and the rest of the seats use the seatbelt latch (vehicle specific).  When you are driving a vehicle the module also monitors the status of seatbelts and the pressure sensors, it uses this data to make the best decision possible about which airbags to deploy and when.

 

2. I’m often asked about a specialists report, but the most common subset questions are about the lack of support for findings in the report.  I have chosen to address this question because it’s of personal & professional interest to me.

“I got this collision expert’s report but there doesn’t appear to be any explanation for his findings, is this normal?”

Yes and No.  Yes, this happens; no, it’s not acceptable standard.  One of the reasons I have chosen to work with Dr. Studin is his tenacious commitment to research.  If you have seen Mark present you know he has scholarly research to back up his points.  Mark and his colleagues have been through accredited and standardized training based on a lot of scholarly research.  All professional fields of post primary education are all based in accredited & scholarly formal standards. 

Collison reconstruction specialists are no different.  While not necessary part of an undergraduate or graduate program, the training and education they have is based on the same accredited & scholarly formal training and education - because of this correlation, the same standard should be applied to collision reconstruction specialists.  Scholarly research is based on objective methods of testing and investigation, peer review, and rigorous scrutiny before being accepted. 

When an expert offers an opinion without citing supporting scholarly documentation it’s not worthless, but rather it stands alone; it is only his opinion.  Conversely, when an expert offers and opinion with appropriate supporting scholarly documentation, all the work, expertise, and research is offered with his opinion.   

3. Often times an appraisal for repairs is used to justify “low speed” by citing minimal costs.  There are a few points regarding them to consider so the question is: 

“Is the listed cost on the appraisal an accurate reflection of damage?”

The short easy answer is “no”.  The long answer starts with understanding who did the appraisal and what is there background?  Usually, appraisers are trained by the insurance company – as such, minimizing the costs and expenses of repair is in the insurance company’s interests.  Secondly, most appraisers do not disassemble a vehicle to determine if there is any hidden damage, particularly in low speed collisions.

The next problem is when replacement parts are needed where do they come from?  Original Equipment Manufacturer (OEM) parts cost substantially more than Equal or Like Quality (ELQ) parts, as such, ELQ parts are the preferred choice of insurance companies.  It would cost the industry millions more to use OEM parts instead of ELQ parts when making repairs.  Along this same line, the quality of paint also varies.  Paint manufacturers offer paint systems which will meet the OEM specifications and are very durable paints, however, they also offer more economically friendly paint which is not as durable or closely color matched to the original, and as expected, it costs less.

The last problem to discuss is job downtime.  The longer a vehicle is in for repairs the more it costs the insurance company in rental fees.  While a shop can, and will, have a minimum amount of time to fix the vehicle the insurance company is going to keep them on this timeframe and constantly press for the vehicle to be completed.  Sometimes this drive can create an environment where the repair facility will sacrifice quality of workmanship to complete the job faster for a better profit margin.

The above variables greatly dictate the final number making it too subjective for a reliable point to support the threshold of injury; in other terms, the use of “low cost” as a justification for no injury is not appropriate as no causality relationship exists.  If a breakdown of the repair bill is provided, you could objectively price the repair parts and effectively show the bias towards reducing the cost of the repair.  

 

Patrick Sundby has decades of experience in the automotive industry including several years in law enforcement collision investigation. He has also been a driver training and firearms instructor in law enforcement and a police officer for 9 years before specializing in accident investigations. He has had the privilege of participating in both learning and teaching at Prince William County Criminal Justice Training Academy in Virginia and studied at the Federal Law Enforcement Training Center in Georgia. His specialty is low speed and catastrophic crashes and has testified over 500 times at various level. He can be reached at 571-265-8076 or This email address is being protected from spambots. You need JavaScript enabled to view it.

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   Tires

  Pressure, Stopping Distance and Causality - Part I

 

By: Patrick Sundby, Accident Investigator

Specializing in Low Speed and Catastrophic Crashes

 

Mark Studin DC, FASBE(C), DAAPM, DAAMLP

 

There is a lot of information regarding tires, so much so this information goes way beyond the recommendations and reviews on the megastore website.  Here we will discuss, from a post-collision perspective, some vehicle specifications, standard tire information, and how tire pressure monitoring systems (TPMS) work.  We will then examine how tire pressures relate to automotive collisions in helping to determine causality.

 

Vehicle Specifications

Vehicles sold in the United States have a placard in the driver’s door jamb or inner door.  This placard contains some information we need to have to explore the tires including the vehicle manufacturer recommended tire size, load rating, and tire pressure.  Here is an example:

 

(There is a second placard specifically for tires but this should be confirmed against the above placard as the second one doesn’t contain any vehicle identifying information such as a VIN.  In this photograph the last six digits of the VIN have been omitted.)

Tire Size

The majority of modern tires have writing on the sidewall which explains the tires dimensions and other important characteristics.  What does it mean?  In the tag above the tire sizes for front and rear are listed.  The 265 is the width, in millimeters, of the tread face.  The next number, 70, is the height of the tire sidewall as a percentage of the tread face (in this case 70% of the 265).  The “R” makes the tire construction a radial.  Finally, the 17 is rim diameter in inches.

Tire Pressure

Notice the listed tire pressure is supposed to be cold.  Tires have to sit for at least eight hours out of direct sunlight before they are considered cold enough for taking a reading.  Gases expand as they are heated and the minimum cold pressure is set so the tire will be at the optimal pressure once at operating temperature; accordingly, if a tire is at or below the minimum and is at operating temperature, the pressure was even lower when the tire was cold.

Tire Pressure Monitoring System (TPMS) 

The TPMS became a mandated standard after the fallout of the Ford Explorer & Firestone tire event.  The federal government wanted a system which would alert drivers to “low” tire pressure(s).  There are two types of systems.  The first type is called “direct measurement” and it uses a sensor inside each tire which wirelessly relays the pressure.  The second type is called “indirect measurement” and it uses the anti-lock brake system to determine if a tire is spinning faster than the others.  A tire with less air pressure will have a smaller diameter and therefore will spin faster; the anti-lock brake system can calculate this difference.

The gap in either system comes when we examine how this system decides to warn the driver.  Because the pressures in a tire can vary for a few reasons (we just discussed how temperature is one of them) the TPMS doesn’t look for a single pressure, but rather a range or minimum pressure.  The parameters setup within the vehicle’s computer only illuminates the warning light if a tire’s pressure is beyond the preselected specifications. 

Many studies by the federal government, independent organizations, and tire manufacturers all support substandard performance of tires where the tires are below the recommended pressure.  The studies referenced at the end of this writing have three points of discussion.

 

71% of drivers check tire pressure less than once a month.

More than 1/3 of passenger cars surveyed had at least one tire at or below 20% of the placard.

Only 36% of vehicles tested would get a warning light at 20% or more below the placard.

 

The first point isn’t a surprise.  The lack of regular tire pressure maintenance is part of why the federal government mandated the TPMS system.  The second point is also not surprising.  If the majority (71%) doesn’t regularly check tire pressure, it should be expected tires are below the recommended pressure.  The final point is the one we want to focus on.  We want to focus on this fact because the majority of passenger vehicle pressures are 30 PSI; 20% less is 24 PSI.

If 100 passenger vehicles were on the road, 36 of them would have at least one tire at least 20% below the placard pressure.  Of the 36 vehicles, only 13 of them would have a warning light.  (For the record it’s not much better for the light truck / SUV category.)

So now we know a third of the vehicles on the road have an underinflated tire and further only a third of those vehicles have a warning light.  Now the question is does 6 PSI matter?  Yes, it does.  Testing done by Goodyear and the NHTSA both confirmed a 20% reduction in pressure results in greater stopping distances, reduction in handling, increase in blowouts, lower fuel economy, and increased tire wear.

Putting it all together      

The National Highway Transportation Safety Administration (NHTSA) also routinely studies tire related collisions.  One study found approximately 9% of all collisions are tire related.  In 2012, out of the 5.6 million police reported collisions, 504,000 were tire related.  

For simplicity, we will assume all of the collisions involved one vehicle making the total 5.6 million.  If we use the percentages from the above table, over 2 million would have at least one underinflated tire, 725,000 would have the warning light.  Increasing the total number of vehicles only increases the subsequent statistics.   

When determining causality, there are 504,000 tire related collisions as reported above and this misunderstood and frequently overlooked fact is historically omitted when attempting to determine the culpable party. It is for this reason that maintenance that tire pressures should be determined immediately post-accident and not just focus on skid marks (although they are equally important in the equation important) as demonstrative evidence when attempting to reconstruct accidents in the quest of determining causality.

In Part 2 we will discuss how these factors influence tire performance that further gives demonstrative evidence to the accident reconstructionist, accident investigator and lawyer.

References

  1. National Highway Transportation Safety Administration. (2012). Traffic Safety Facts 2012. Retrieved from http://www-nrd.nhtsa.dot.gov/Pubs/812032.pdf
  2. National Highway Transportation Safety Administration. (2013, june 28). SAFETY ADVISORY: NHTSA Urges Drivers to Check Tires During Hot Weather. Retrieved from http://www.nhtsa.gov/About+NHTSA/Press+Releases/SAFETY+ADVISORY:+NHTSA+Urges+Drivers+to+Check+Tires+During+Hot+Weather
  3. National Highway Transportation Safety Administration. (2013, June). The Problem. Retrieved from http://www.nhtsa.gov/nhtsa/Safety1nNum3ers/june2013/theProblemJune2013.html
  4. National Highway Transportation Safety Administration. (n.d.). TIRE PRESSURE SURVEY AND TEST RESULTS. Retrieved from http://www.nhtsa.gov/cars/rules/rulings/TirePressure/LTPW3.html
  5. National Highway Transportation Safety Administration. (n.d.). Tire Pressure Final. Retrieved from http://www.nhtsa.gov/cars/rules/rulings/tirepresfinal/safetypr.html

 

Patrick Sundby has decades of experience in the automotive industry including several years in law enforcement collision investigation. He has also been a driver training and firearms instructor in law enforcement and a police officer for 9 years before specializing in accident investigations. He has had the privilege of participating in both learning and teaching at Prince William County Criminal Justice Training Academy in Virginia and studied at the Federal Law Enforcement Training Center in Georgia. His specialty is low speed and catastrophic crashes and has testified over 500 times at various level. He can be reached at 571-265-8076 orThis email address is being protected from spambots. You need JavaScript enabled to view it.

Dr. Mark Studin is an adjunct associate professor of chiropractic at the University of Bridgeport College of Chiropractic, an Adjunct Professor of Clinical Sciences at Texas Chiropractic College and a clinical presenter for the State of New York at Buffalo, School of Medicine and Biomedical Sciences for postdoctoral education, teaching MRI spine interpretation and triaging trauma cases. He is also the president of the Academy of Chiropractic, teaching doctors how to interface with the legal community (www.DoctorsPIProgram.com). He teaches MRI interpretation and triaging trauma cases to doctors of all disciplines nationally, and studies trends in health care on a national scale (www.TeachDoctors.com). He can be reached atThis email address is being protected from spambots. You need JavaScript enabled to view it.or at 631-786-4253.

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Conservation of Momentum:

Where does it go, Part II.

 

By: Patrick Sundby, Accident Investigator

Specializing in Low Speed and Catastrophic Crashes

Mark Studin DC, FASBE(C), DAAPM, DAAMLP

 

In the previous writing we explored the standards for vehicle integrity during low speed collisions.  In this writing we will expand on Conservation of Momentum.  If you have not read the previous article you are encouraged to do so.  While it’s not necessary to read it doing so will assist you as this writing will build on concepts contained within.  If you do not have it, please contact us and we will make it available to you.

Expand on Conservation of Momentum.

Remember we previously said “The momentum going into a collision can be accounted for in the outcome” when we discussed the concept of Conservation of Momentum.  Here we will introduce the formula and walk through its components; we will need to understand this in order to explore how different size vehicles affect each other in a collision.

The full formula:

Let’s walk through this, on the left side of the equation we have  which is the weight of the first vehicle before the collision multiplied by  which is the velocity (in feet per second) of the first vehicle before the collision.   is the weight of the second vehicle before the collision times  which is the velocity (in feet per second) of the second vehicle before the collision.  On the right side of the equation we have  which is the weight of the first vehicle after the collision multiplied by  which is the velocity (in feet per second) of the first vehicle after the collision.   is the weight of the second vehicle after the collision times  which is the velocity (in feet per second) of the second vehicle after the collision.

Ok, I know this seems very complex and the explanation is not jumping off the page so let’s write with a little more ease of understanding.  Let’s take the National Highway Transportation Safety Administration (NHTSA) standards for testing and put two of the same mass vehicles in this.  Let’s use a 2012 Toyota Corolla, and because we need two of them we will say one is red and the other is blue.

Red Corolla * 5 mph + Blue Corolla * 0 mph = Red Corolla * 0 mph + Blue Corolla * 5 mph

The 2012 Toyota Corolla has a curb weight of 2,734 pounds, substituted in the formula it looks like this:

2,734 lbs * 5 mph + 2,734 lbs * 0 mph = 2,734 lbs * 0 mph + 2,734 lbs * 5 mph

We need the speeds in feet per second, to do this we will multiply by 1.47 times the miles per hour.  This gives us 7.35 feet per second.

2,734 lbs * 7.35 fps + 2,734 lbs * 0 fps = 2,734 lbs * 0 fps + 2,734 lbs * 7.35 fps

Now when we do the math to show the conservation of momentum we end up with the following:

20,094.9 + 0 = 0 + 20,094.9

20,094.9 = 20,094.9

Momentum conserved.

Now we have proved the concept so we are going to apply it to a collision involving two different vehicles.  We will substitute the 2012 red Toyota Corolla for a 2012 red Chevrolet Tahoe.  The 2012 Chevrolet Tahoe weighs 5,448 lbs.  Now the formula looks like this:

Red Tahoe * 5 mph + Blue Corolla * 0 mph = Red Tahoe * 0 mph + Blue Corolla * 9.96 mph

5,448 lbs * 5 mph + 2,734 lbs * 0 mph = 5,448 lbs * 0 mph + 2,734 lbs * 9.96 mph (speed after impact)

We need speeds in feet per second, to do this we will multiply by 1.47.  This gives us 7.35 (5mph) and 14.64 (9.96mph).

5,448 lbs * 7.35 fps + 2,734 lbs * 0 fps = 5,448 lbs * 0 fps + 2,734 lbs * 14.64 fps

Now when we do the math to show the conservation of momentum we end up with the following:

40,042.8 + 0 = 0 + 40,042.8[1]

40,042.8 = 40,042.8

Momentum conserved.

Three important points can be observed in this demonstration. 

First, when testing is done note the change in speed in the Tahoe is 5 mph (5 to 0).  This is less than the speeds used by the Insurance Institute for Highway Safety which we have previously discussed and we would expect the Tahoe to have no structural deformation and minimal cosmetic damage.

The second point to note is the change in speed the Corolla experiences, 9.96 mph (0 to 9.96).  This change in speed is four times the minimum needed to induce whiplash injury.

Finally, neither vehicle exceeds the speed of 10 mph, which the auto manufactures and insrunace institute for highway safety often consider threshold for injury. This confirms that cars can easily deform and occupants get injured in low speed crashes once you begin to look at the conservation of energy (momentum) and coefficient of forces transferred to the target car.

Should you want a further explanation or to discuss a case, please contact me 571-265-8076

 

 

References

Edmunds.com. (2012). 2012 Chevrolet Tahoe Specifications. Retrieved from Edmunds.com: www.edmunds.com

Edmunds.com. (2012). 2012 Toyota Corolla Sedan Specifications. Retrieved from Edmunds.com: www.edmunds.com

Brault J., Wheeler J., Gunter S., Brault E., (1998) Clinical Response of Human Subjects to Rear End Automobile Collisions. Archives of Physical Medicine and Rehabilitation, 72-80.

 

Patrick Sundbyhas decades of experience in the automotive industry including several years in law enforcement collision investigation. He has also been a driver training and firearms instructor in law enforcement and a police officer for 9 years before specializing in accident investigations. He has had the privilege of participating in both learning and teaching at Prince William County Criminal Justice Training Academy in Virginia and studied at the Federal Law Enforcement Training Center in Georgia. His specialty is low speed and catastrophic crashes and has testified over 500 times at various level. He can be reached at 571-265-8076 or This email address is being protected from spambots. You need JavaScript enabled to view it.

Dr. Mark Studinis an adjunct associate professor of chiropractic at the University of Bridgeport College of Chiropractic, an Adjunct Professor of Clinical Sciences at Texas Chiropractic College and a clinical presenter for the State of New York at Buffalo, School of Medicine and Biomedical Sciences for postdoctoral education, teaching MRI spine interpretation and triaging trauma cases. He is also the president of the Academy of Chiropractic, teaching doctors how to interface with the legal community (www.DoctorsPIProgram.com). He teaches MRI interpretation and triaging trauma cases to doctors of all disciplines nationally, and studies trends in health care on a national scale (www.TeachDoctors.com). He can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it. or at 631-786-4253.

 


[1] If the formula is completed with rounded numbers the answer is 40,025.76 not 40,042.8.  The full numbers are not shown, but used, to ensure a match at the end of the equation.

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Conservation of Momentum:

Where Does the Energy Go, Part 1

 

By: Patrick Sundby, Accident Investigator

Specializing in Low Speed and Catastrophic Crashes

Mark Studin DC, FASBE(C), DAAPM, DAAMLP

 

There are many factors which play a role in the dynamics of automotive collisions.  These include vehicle design and type, speeds, angles of approach, kinetic & potential energy, momentum, acceleration factor, friction… the list is very long. However, there are a few constants in which we are most interested.  These constants are the building blocks of our world and they make the chaotic world of automotive collisions predictable and quantifiable.

In this two-part series we will explore the factors which have the most influence in low speed collisions and how these factors are related to injury.  Note: nothing about these writings is inclusive, there is simply too much material to explore, much less explore in depth.  The goal of these writings is to introduce the concepts to you.

In this writing the topic of exploration is Conservation of Momentum and how it relates to low speed collisions and bodily injury of the occupant.  Conservation of momentum is built on Sir Isaac Newton’s third law.  Newton’s third law states “For every action there is an equal and opposite reaction”.

In the interest of exploring conservation of momentum in a simple format, we are not going to explore and explain the history and physics of momentum; for this conversation, we will focus on the relationship to crash dynamics. It is the relationship of momentum to low speed collisions that is the causal factor of the injuries and helps enlighten those who have held tight to the deceptive argument that no damage = no injuries.

While there is a formula and derivation, neither is needed just yet.  For now, we will simply use the concept as follows: The momentum going into a collision can be accounted for in the outcome or the energy going in to the accident, must be accounted for at the end of the incident and who and what was exposed to and/or absorbed that energy.

Let’s apply some perspective to the concept with the following example.

Let’s say we are standing at around a pool table and we are going to attempt the winning shot of the eight ball into a corner pocket.  After the cue ball is struck, we now have one object in motion which will collide with another.  When the cue ball strikes the eight ball, it stops moving and the eight ball begins moving.  In this scenario the momentum of the cue ball before the collision is the same as the momentum of the eight ball after the collision[1].  The eight ball rolls into the corner pocket.

The transfer is highly efficient due in part to the fact that neither pool balls can deform.  If either pool ball could deform, some of the energy would be used to do this and less would be transferred to make the ball roll.  The National Highway Transportation Highway Safety Administration (NHTSA) mandates minimum performance standards for passenger vehicle bumpers.  Vehicle bumpers are tested with 2.5 mph (3.7 fps)[2] impact equipment which has the same mass as the test vehicle.  The test vehicle is struck with its brakes disengaged and the transmission in neutral.  There is no offset between the vehicle and the barrier. 

The NHTSA outlines acceptable damage to a vehicle’s various systems after the tests.  Successful completion of these tests mandate normal operation of certain systems. The factory adjustment of the vehicle’s braking, steering, and suspension must be unaltered.  In other terms, in order for a vehicle to pass these tests it cannot have any change in its structure.  If changes did occur the braking system, steering, and suspension would be out of factory adjustment.

The NHTSA is not alone in low speed bumper testing.  The Insurance Institute for Highway Safety (IIHS) also conducts low speed bumper tests.  The IIHS’s test speeds are conducted at 6 mph (8.8 fps)[3] and the goal is to determine which vehicles have the least damage and therefore cost the least to repair.  The vehicle ratings are inversely proportional to the estimated cost of repair. The costlier the repair, the lower the rating, exclusive of safety.

While the vehicles used in the IIHS testing all show signs of contact with the barrier, none of the vehicles suffer damage which deforms the structure of the vehicle.  Just as with the NHTSA the vehicles tested by the IIHS do not have any change in its structure affecting the braking system, steering, and suspension.

The lack of change in the structure (deformation) forces a test vehicle to accept the momentum transfer from the testing equipment.  Further, the test vehicle is free to move after being struck.  This testing scenario is strikingly similar to that of the cue ball and eight ball.

If a vehicle doesn’t deform during a low speed collision, then it will experience a change in speed (or velocity) very quickly; Accordingly, the occupant(s) also experience this same change in speed.  The key factor in these examples is the equal mass of the vehicles and testing equipment involved, but what happens when the masses change?

When the mass of one vehicle changes the momentum also changes, the more mass the more momentum the vehicle can bring to the event and the greater the injury potential to the occupant. There are many complicating factors that now must be considered regarding injuries beyond the Laws of Momentum when determining injury such as the height, weight, muscle mass, occupant position, type of seat belt used, etc. However, the first step is to determine if there was enough energy as an initiating factor in low speed crashes to cause those injuries and to overcome those no crash = no injury misconceptions and then have a medical expert in low speed injuries confirm causal relationship.

In the next installment, part II, we will discuss this in detail and it will necessary for the later topic of occupant injuries.

REFERENCES:

  1. Insurance Institute for Highway Safety. (2010, September). Bumper Test Protocol. Retrieved from Insurance Institute for Highway Safety: www.iihs.org
  2. National Highway Transportation Safety Administration. (2011, October 1). 49 CFR 581 - BUMPER STANDARD. Retrieved from U.S. Government Publishing Office: www.gpo.gov

Patrick Sundby has decades of experience in the automotive industry including several years in law enforcement collision investigation. He has also been a driver training and firearms instructor in law enforcement and a police officer for 9 years before specializing in accident investigations. He has had the privilege of participating in both learning and teaching at Prince William County Criminal Justice Training Academy in Virginia and studied at the Federal Law Enforcement Training Center in Georgia. His specialty is low speed and catastrophic crashes and has testified over 500 times at various level. He can be reached at 571-265-8076 or This email address is being protected from spambots. You need JavaScript enabled to view it.

Dr. Mark Studin is an adjunct associate professor of chiropractic at the University of Bridgeport College of Chiropractic, an Adjunct Professor of Clinical Sciences at Texas Chiropractic College and a clinical presenter for the State of New York at Buffalo, School of Medicine and Biomedical Sciences for postdoctoral education, teaching MRI spine interpretation and triaging trauma cases. He is also the president of the Academy of Chiropractic, teaching doctors how to interface with the legal community (www.DoctorsPIProgram.com). He teaches MRI interpretation and triaging trauma cases to doctors of all disciplines nationally, and studies trends in health care on a national scale (www.TeachDoctors.com). He can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it. or at 631-786-4253.


[1] Some factors are acknowledged but not discussed for ease of concept explanation.

[2] 1 mph = 1.47 fps, 2.5 mph * 1.47 = 3.7 fps

[3] 1 mph = 1.47 fps, 6 mph * 1.47 = 8.8 fps

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