Our accident attorneys in Charleston have seen that in automobile accident cases where there is little property damage to the vehicles, insurance defense attorneys are quick to argue that was impossible for the accident victim to be injured. In these cases, insurance defense attorneys hire a biomechanics engineer or another “expert” to express an opinion that the physical forces involved in the accident couldn’t have caused the victim’s injuries. Here, we explore some of the “science” used by these defense experts and detail 10 major ways that their “expert” opinions may be flawed.

The Science Relied Upon by Biomechanical Defense Experts

An expert’s opinion, such as the opinion of a biomechanics engineer, is based on upon analyzing: (1) the forces impacting the vehicles; (2) the forces impacting the victim’s body; and (3) human tolerance values (how much force a human body can absorb without injury).

1. Forces Impacting the Accident Vehicles – deltaV

The forces that impact a vehicle in an accident is referred to as “deltaV.” In a rear-end collision where a vehicle is stopped and is hit from behind by another vehicle, the impact’s force accelerates the struck or stopped vehicle forward from zero miles per hour to “x” miles per hour. That acceleration speed (velocity) of the struck vehicle is a positive deltaV. Meanwhile, the vehicle that struck the stopped car loses velocity and experiences a negative deltaV.

To calculate deltaV, most biomechanics experts use software such as CRASH III in which they input data about the vehicles, the accident site, and the vehicle damage (crush). From the calculation of deltaV, the expert can then calculate the g-forces involved in the accident. G-force is a measurement of the force to which a body is subjected when it is accelerated.

2. Forces Impacting the Accident Victim’s Body – Human Dynamics Analysis

After deltaV is calculated, the insurance company’s expert will calculate what impact deltaV and g-forces had on the vehicle’s occupant. This calculation is known as “human dynamics analysis.” Like calculating deltaV, the engineer will input into a software program information about the deltaV and g-force along with other data to calculate whether the accident could have caused the plaintiff’s injuries. Some of the data that is input into these software programs, such as the Articulated Total Body (ATB), include the occupant’s height and weight, the stiffness of the occupant’s seat, the location of the seat’s headrest, and data regarding how the occupant was seated in the vehicle.

3. Human Tolerance Values of the Accident Victim

Generally speaking, defense biomechanical testimony is very similar. These experts testify that an injury was impossible because the accident delivered a force upon the victim that was less than the threshold of force necessary to cause injury. In support of this testimony, many expert refer to a short list of studies that conclude that “low-speed” accidents do not cause injury to human beings. Two of these studies are: (1) “Low Speed Rear-End Collision Testing – Using Human Subjects,” by D.H. West and (2) “Acceleration Perturbations of Daily Living-A Comparison To ‘Whiplash’,” by Murray E. Allen. West used human volunteers subjects who were exposed to the forces of low-speed rear impacts up to and exceeding 5 mph barrier impacts. West concluded that if the equivalent fixed barrier speed (EBS) of the impact was less than 3 mph, these forces couldn’t cause injuries anymore so than a person’s routine, daily life activities. Allen investigated the repeated human head acceleration g’s that occurred during daily activities. Using eight volunteers, Allen compared thirteen daily activity g-forces to low-velocity, rear-end motor vehicle accidents. Like West, Allen concluded that the forces of low velocity, no damage impacts cause little injury to the victim of such accidents..

10 Challenges to the Defense Expert

1. Is the “Expert” Qualified?

There are many experts, such as former police officers, who are qualified to testify as to accident reconstruction and calculation of deltaV and g forces. However, some of these experts will venture into the area of giving their opinions on injuries in low-impact automobile accidents without any background or formal training in biomechanics engineering, human anatomy, human dynamics, or human tolerance values.

2. Is the Expert Relying on CRASH III Data?

According to the creator of the CRASH III software, the data it relies on involved crash tests of over 20 mph deltaV and is designed for studying collisions regarding a deltaV of 10 to 40 mph. Therefore, it is improper for an expert to rely on CRASH III in a low-impact case (deltaV of less than 5 mph).

3. Is the Expert Relying on Neptune Engineering Data?

In calculating deltaV, an expert needs to consider the vehicle’s “stiffness coefficient” (how hard or soft the vehicle is). Some experts will rely on data collected by Neptune Engineering. However, Neptune’s study used high-speed collisions with higher deltaV. In a high-speed impact, there is more “crush” of much stiffer parts of the vehicle, such as the vehicle frame, then less stiffer parts such as the bumpers. In other words, because Neptune analyzed high-speed collisions, it’s data is useless for low-speed automobile accidents and, if used by the expert, will low-ball the calculation of deltaV.

4. Is the Expert Relying on “Average” G-Force?

In an automobile collision, the g-forces involved begin at the moment of impact, increase to a “peak” g-force, and then subside as the vehicles come to rest after the accident. In other words, there is a point during the collision when the g-forces involved are at their greatest impact on the accident victim. However, some experts will downplay the significance of the victim’s injuries by relying on the “average” g-force of the accident which is much less than the “peak” g-force.

5. Is the Expert Ignoring the G-Force on the Victim?

Oftentimes, although the expert calculates deltaV and the g-force impact on the vehicle, they ignore the g-forces applied to the vehicle’s occupant. G-forces imposed on a vehicle will not impose the same force on the vehicle’s occupants. In fact, oftentimes the g-force imposed on the occupants is HIGHER than on the vehicle.

6. Is the Expert Ignoring the Laws of Physics?

One principle of physics is that all energy in a collision must be “conserved” (i.e., it has to go somewhere). Insurance defense experts will conclude that because the energy in the accident didn’t cause property damage, the energy level was insufficient to cause injury to the victim. This conclusion is flawed. In an accident, energy can be transferred in several ways other than property damage. For example, sometimes the vehicles will move after the impact or the vehicles themselves absorb some of the energy. More importantly, some of the energy is transferred to the occupants.

7. Is the Expert Underestimating the Accident’s Duration?

Most accidents take place within milliseconds. The impact of g-forces on the victim varies depending upon the accident’s duration. Some experts don’t actually calculate the accident’s duration, which could be as little as 60 milliseconds, but instead use a range of 100-120 milliseconds. Using this range is improper because the shorter the duration, the greater the impact on the human dynamics aspect of the collision.

8. Is the Expert Relying on Flawed Studies?

Allen’s 8 test subjects were healthy men (4) and women (40) 19 to 50 years old. West’s subjects were all healthy males from 25 to 43 years old. The point is that the victim’s physiology may be very different from these test subjects. For example, the accident victim may have a previous back injury or they might be very young or older than the test subjects. Also, the victim may be seated in a different position than these test subjects. Changing one variable can significantly effect whether the accident victim suffers serious injuries or not.

Allen compared low-speed accidents to the forces of daily activities such as sneezing, standing up from a seated position, or hopping off of a step. However, comparing these daily events to an auto accident’s events is like comparing apples to oranges. For example, in a vehicle, seat belts and headrests effect and restrict an occupant’s movement. Plus, according to other studies, our bodies can tolerate more vertical force than horizontal force. Yet, Allen compares the VERTICAL forces involved in daily activities such as standing up to the HORIZONTAL forces of an automobile accident. Also, these studies don’t account for variations of a victim’s position within the vehicle such as whether the victim’s head was turned to the side during the accident thereby causing their neck to be more prone to injury.

Also, studies such as those by Allen and West have been criticized by other experts in the field of biomechanics. For example, in “A Review and Methodologic Critique of the Literature Refuting Whiplash Syndrome,” by Michael Freeman, Freeman points out several flaws in other studies relied upon by defense experts. These flaws include inadequate sample sizes, inappropriate study designs, selection bias, conclusions unsupported by results, misquoted literature cited in the study, study samples unrepresentative of real-life crash victims, and unrealistic crash conditions.

9. Is the Expert Relying on Federal Bumper Standards?

In some cases, the insurance company’s defense expert will rely on Title 49 of the Code of Federal Regulations, Part 581. This federal regulation requires passenger vehicles manufactured from 1974 through 1982 to have front and rear bumpers that could sustain impacts with a barrier at 5 mph (and 1983 to present to sustain a 2.5 mph front or rear impact with a barrier). If there is no property damage, the defense expert will conclude that the speed must have been under the Federal standard of 5 mph and, consequently, deltaV was less than 5 mph. The problem with this “expert” opinion is that most modern vehicle bumper systems can experience a deltaV of 10 mph without any structural damage.

10. Is the Expert Conducting a “Boiler-Plate” Analysis?

In the real world, one size does NOT fit all. Real world accidents involve infinite variables whereas lab studies are conducted using defined and controlled variables. However, it is not uncommon to see reports from defense biomechanical experts, such as experts from SEA, LTD., who incorporate boiler-plate analysis of “low-speed impact” cases into their reports. So, the expert should be questioned in a deposition as to what information he or she relied on in reaching their conclusions about the force imposed upon the accident victim. Some areas worth exploring are:

  • The victim. The more muscular the victim is, the less potential for injury and visa versa. Additionally, the victim may have medical conditions or issues that make them more susceptible to injury. Moreover, studies indicate that women are at greater risk of injury than men.
  • The victim’s body position. During impact, was the occupant twisting in their seat, reaching for something in the vehicle, leaning to the side, etc.? Remember, when the head is extended or turned from a neutral, forward-facing position, then the neck’s range of motion is decreased, the strains on the supporting ligaments is greater, and the potential for injury is much higher. Also, was the victim braced for impact? A body tensed for impact protects better against injury.
  • Seat back and head rest positions. Head-restraints don’t always prevent injuries. Medical evidence shows that the initial movement of a portion of the cervical spine relative to the rest of the spine causes injuries. So, whether a headrest prevents the victim’s head from moving backward to the point of excessive flexion or extension may be irrelevant. If the expert doesn’t know the position of the headrest and the seat back relative to the victim’s body, then it is impossible for the expert to determine the extent of the victim’s body movement before striking, if at all, the headrest or the seat back. Further, as stated by the Insurance Institute for Public Safety, small differences in adjustment of the headrest and seat back can make a significant difference in the amount of force imposed upon the occupant in an accident. Finally, because a rear end collision projects the upper body forward, it is the seat back that creates the initial movement. The seat back can create a “trampoline” effect that accentuates the acceleration. One study suggests that this effect can DOUBLE the g-force imposed upon the victim’s spine.
  • Seat belts. Seat belts are useless or even harmful if improperly positioned. For example, shorter people who wear the shoulder portion higher toward the neck are at higher risk for injury.
  • Angle and direction. Not every rear-end collision occurs from straight behind. If the striking vehicle turns before impact, a twisting force is applied to the victim’s vehicle. Consequently, the impact can cause a twisting of the seat back and decrease the seat’s ability to safely cradle the occupant. In this situation, the victim’s head may miss the head restraint or strike something else in the vehicle’s interior such as a side window.
  • Ramping effect. In a rear-end collision, the victim’s body may move up as well as backward during the impact. This “ramping effect” increases the likelihood of cervical injury.

Final Thoughts

Don’t be thrown off track by an insurance company’s biomechanical defense expert. Relying on studies, computer software, and physics calculations, these experts can sound very convincing when they conclude that NO injury was possible in a traffic accident. If you dig deep enough, you can expose the flaws in the studies these experts rely on, illustrate the lack of real-world analysis of all of the variables in the accident, and defuse attempts by some experts to skew their calculations to support the defense.

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