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

Share this

Submit to DeliciousSubmit to DiggSubmit to FacebookSubmit to Google BookmarksSubmit to StumbleuponSubmit to TechnoratiSubmit to TwitterSubmit to LinkedIn



Arthritis Prevention and Chiropractic  

Chiropractic prevents arthritis in accident victims, the elderly and the sedentary

A report on the scientific literature 


According to the Arthritis Foundation (2007), "Forty-six million [46,000,000] Americans are currently living with arthritis, the nation's leading cause of disability, and we are all paying a high price for it. The Centers for Disease Control and Prevention (CDC) announced that the annual cost of arthritis to the United States economy was $128 billion in 2003 and increased by $20 billion between 1997 and 2003.

CDC attributes the dramatic increase to the aging of the population, predominantly baby boomers, and increased prevalence of arthritis. CDC also estimates an additional 8 million new cases of arthritis will be diagnosed in the next decade" (

Arthritis, A.D.A.M., Inc. (2010, February 5), " inflammation of one or more joints, which results in pain, swelling, stiffness, and limited movement. There are over 100 different types of arthritis...

Causes, incidence, and risk factors

Arthritis involves the breakdown of cartilage. Cartilage normally protects the joint, allowing for smooth movement. Cartilage also absorbs shock when pressure is placed on the joint, like when you walk. Without the usual amount of cartilage, the bones rub together, causing pain, swelling (inflammation), and stiffness.

You may have joint inflammation for a variety of reasons, including:

- An autoimmune disease (the body attacks itself because the body immune system believes a body part is foreign)
- Broken bone
- General wear and tear
- Infection (usually cause by bacteria or viruses)... 

With some injuries and diseases, the inflammation does not go away or destruction results in long-term pain and deformity. When this happens, you have chronic arthritis. Osteoarthritis is the most common type and is more likely to occur as you age. You may feel it in any of your joints, but most commonly in your hips, knees or fingers. Risk factors for osteoarthritis include:

- Being overweight
- Previously injuring the affected joint
- Using the affected joint in a repetitive action that puts stress on the joint (baseball players, ballet dancers and construction workers are all at risk)

Arthritis can occur in men and women of all ages. About 37 million people in America have arthritis of some kind, which is almost 1 out of every 7 people" ( With hypomobility (less mobility or movement), adhesions occur in a joint (the region where 2 bones connect).

According to A.D.A.M., Inc. (2010, March 30), "Adhesions are bands of scar-like tissue that form between two surfaces inside the body and cause them to stick together. As the body moves, tissues or organs inside are normally able to shift around each other. This is because these tissues have slippery surfaces.

Causes, incidence, and risk factors

Inflammation (swelling), surgery, or injury can cause adhesions to form almost anywhere in the body...Once they form, adhesions can become larger or tighter over time. Symptoms or other problems may occur if the adhesions cause an organ or body part to twist, pull out of position, or be unable to move as well.

Adhesions may form around joints such as the shoulder...or ankles, or in ligaments and tendons. This problem may happen:

- After surgery or trauma
- With certain types of arthritis
- With overuse of a joint or tendon


Adhesions in joints, tendons, or ligaments make it harder to move the joint and may cause pain...Adhesions in the pelvis may cause chronic or long-term pelvic pain.

Signs and tests

Most of the time, the adhesions cannot be seen using x-rays or imaging tests" (

Over time, with a sedentary lifestyle as seen in many portions of the population and increasingly with the elderly, joints become hypomobile. Hypomobility is also seen in trauma-related cases and repetitive use injuries, such as reading while looking down for extended periods, carrying heavy items, holding the phone between one's shoulder and ear, prolonged use of hands, wrists, back and neck, excessive use of computers, etc. As time progresses, internal scar tissue or adhesions continue to develop and further increases the loss of mobility.

Cramer, Henderson, Little, Daley and Grieve (2010), cite previous studies that have shown that adhesions have been found in numerous hypomobile (loss of normal movement) joints and that spinal adjusting separates the articular surfaces of the joint. The researchers inquired as to whether connective tissue adhesion developed in lumbar articular joints as a consequence to intervertebral hypomobility and utilized animal studies.  They concluded that "...hypomobility results in time-dependent [adhesions]..." (Cramer et al., 2010, p. 508). In other words, internal scar tissue (arthritis) developed within the joints over time.

Cramer et al. (2010) sited previous studies that found the spinal adjustment separates the joints which could break up intra-articular adhesions. In other words, in their animal studies, spinal adjustments/manipulation increased the "Z gap" or spacing between the joints/bones and the mobility of the joints. If this applied in humans, the adjustments would then prevent further development of adhesions and degeneration and osteophytes, which is how the arthritic process progresses.

While arthritis affects approximately 1 in 7 Americans, the prevention of and/or correction of arthritis would relieve a great strain on our economy. While not all arthritis is a result of hypomobility, much of it is. If every person was under chiropractic care, we could not only positively affect the lives of every American, we could potentially rescue the economy of the United States and every other country and insurer in the world that assumes risk for an aging and hypomobile society.



1. Arthritis Foundation. (2007, January 17). Cost of arthritis increases to $128 billion annually. Retrieved from

2. A.D.A.M., Inc. (2010, February 5). Arthritis. Retrieved from

3. A.D.A.M., Inc. (2010, March 30). Adhesion. Retrieved from

4. Cramer, G. D., Henderson, C. N. R., Little, J. W., Daley, C., & Grieve, T. J. (2010). Zygapophyseal joint adhesions after induced hypomobility. Journal of Manipulative and Physiological Therapeutics, 33(7), 508-518.

Share this

Submit to DeliciousSubmit to DiggSubmit to FacebookSubmit to Google BookmarksSubmit to StumbleuponSubmit to TechnoratiSubmit to TwitterSubmit to LinkedIn
Published in Arthritis