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Shaw Chiropractic
A Medical-Legal Newsletter for Personal Injury Attorneys
by Dr. Steven W. Shaw

Does No Vehicle Damage Mean No Injury?

As more scientific research becomes available low property damage motor vehicle accidents becomes easier to defend. A current paper published in the Society of Automotive Engineers (SAE) by M.C. Murray now explains why occupant injuries frequently occur in vehicles with little or no visible property damage.

The author in his paper titled Lack of relationship between vehicle damage and occupant injury ( SAE 970494) points out that "A common misconception formulated is that the amount of vehicle crash damage due to a collision offers a direct correlation to the degree of occupant injury. This paper explores this concept and explains why it is false reasoning...[and will] show how minor vehicle damage can relate or even be the major contributing factor to occupant injury.

To appreciate and understand this concept one must recognize that the acceleration that a car experiences is inversely related to how long the car moves before it comes to a stop--or the crush distance in a collision. This is mathematically expressed as:

A=V2/2S
A = acceleration
V = velocity of impact
S = the crush distance

Let's examine two different scenarios to illustrate this concept. In the first situation, we have a car that hits a solid brick wall at 10 mph (4.46 meters/sec) and crushes the front of the car 5 inches (.127 meters). In the second scenario, let's keep the speed at 10 mph, but because of a different car design, the crush in this instance is only 2 inches (.0254 meters).

In the first example A is found to be 78.3 m/sec2 (4.46 x 4.46/2 x .127), or 8 G’s of force. In the second example A is found to be 196 m/sec2 (4.46 x 4.46/2 x .0508), or 20 G’s of force. Thus, a collision with the same velocity, but with a crush amount smaller by 2.5 times will have a resulting G force 2.5 times larger.

Murray sums up this relationship as it relates to whiplash-type injuries:

" ...on a vehicle with a chassis, no serious visual deformation may occur even though it is subjected to relatively high speeds of impact. Classically, we see this in the case of pickup trucks or all-terrain vehicles that are traditionally fitted with a solid bumper-to-bumper chassis. Many of these types of vehicles are subjected to relatively severe impacts with little or no resulting damage to their bodies and bumpers. The classic whiplash injury associated with a great deal of litigation is most likely founded on the reasoning that if there was little or no vehicle damage, no injury can result. Motor vehicle bodies or bumper-to-bumper chassis offer little or no crushing effect on arresting obstacles when impacted; thus, relatively high G forces can be experienced by occupants when rear-ended, resulting in whiplash injury. The use of stiff motor vehicle bodies and chassis will also produce a spiked G force loading to occupants, even if little damage occurs to vehicle body or chassis."

Engineering test collisions consistently show that the peak vehicle G forces in a collision are approximately twice as high as the average G forces, and that peak occupant G forces are about twice as large as peak vehicle forces. Thus, an occupant in a low speed collision with no damage to the vehicle may be at a significantly higher risk of injury than an occupant in a collision with a damaged vehicle.

Once again science has demonstrated that the arguments used by defense council regarding property damage have no basis as it relates to the absolute laws of physics. Unfortunately, these concepts while absolute are not easily communicated to a jury or an adjuster who often times lack the education or desire to appreciate injury and vehicle dynamics. We recommend that if you plan to introduce this type of evidence you make sure that you:

1. Review and understand the technical concepts with your expert witness so that you can smoothly perform a direct examination. This also becomes valuable during cross examination of the defense expert witness who may not be prepared for your technical knowledge in their field.

2. Develop, with your expert witness, the line of questioning that best presents the physics concepts to a jury in a logical and easily understandable fashion. Use metaphors and props that produce a mental and visual picture of the physical relationships so that jurors recall the logic during their deliberation.

3. Properly disclose your expert witness to the court and defense council If you plan to use a physician rather than an accident reconstructionist or physicist. Be prepared to voire dire the physician regarding his training in physics and education in injury dynamics.