Low Speed Collision – Biomechanical Considerations
Each low speed impact accident must be treated individually. There are too many factors to allow easy generalization. Dr. Herzog, who is the associate Dean of Research at the Faculty of Human Kinesiology at the University of Calgary, has criticized the “conventional linear momentum” approach used by accident reconstruction engineers in low speed impacts. Dr. Herzog’s evidence was accepted and instrumental in determining the outcome in the low impact scenario presented in Bourassa v. Ryan (a recent case from the Alberta Court of Queen’s Bench). The conventional linear momentum approach assumes that the direction of force is always horizontal, but accident reconstruction photographs show that there is movement upward inside the cab of an automobile; thus, the “vertical acceleration” factor must be taken into account. Dr. Herzog is of the opinion that to explain the consequences of any impact by only applying the conventional linear model is so inaccurate as to be unethical.
Factors which should also be included in the calculation of the force involving collisions include:
1. The strength of the biological materials. Biological materials can vary according to the following items: age, over use/disuse, gender, previous injury, degenerative disease (i.e., osteoporosis).
2. The position of the victim at the time of the accident; i.e., whether the head was turned or bending down at the time of impact can make a very substantial difference in how the injured person will be affected;
3. The time over which the collision took place; the change of speed means little without taking into account the time period during which the change of speed occurred. For example, the time over which a collision takes place involving two cars moving in the same direction, is different from a collision involving a stopped car or head-on collision;
4. The fact that a lighter vehicle will undergo more “acceleration” after collision than would a heavier vehicle, especially where a light vehicle is hit by a heavy vehicle.
Also, the British Columbia Supreme Court in Reilander v. Kuller  B.C.J. No. 2337, October 6, 1998 commented as follows:
“Even though slight or no physical damage is caused to the automobile as a result of the motor vehicle collision, the injuries to operators and passengers in the vehicles involved in the motor vehicle collision may be extensive. Each case must be heard on its own merits but at law no principle exists that would correlate injuries to physical damage. Physical damages are but one part of the assessment of damages sustained by the Plaintiff”.
As well, Tjell reported that recent studies (1998) have provided improved understanding as to why people involved in low-speed collisions may develop pronounced sympomology. They found that collisions with speeds as low as 10kph can result in significant cervical spine injury. This was particularly true when the force of the impact was not sufficient to result in deformation of the vehicle, resulting in all of the kinetic energy being transmitted to the occupant. The author estimated that the total kinetic energy transferred to the occupant would be approximately equal to twice the speed of the impact. Vehicles deforming as a result of the injury absorb significant impact forces, thus reducing the amount transmitted to the occupant. See B.S. Myers and Winkelstin B.A. in “The Biomechanics of Cervical Spine Injury and Implications for Injury Prevention” Medicine & Science in Sports & Exercise (1997).
The Effect of Low Impact
With respect to an argument that the low impact and minimal damage to the vehicles automatically means that a human being should not have been injured (as if there is a correlation between bolts and steel and blood and tissue) it should be noted that low impact collisions have in fact been quite favourably received by the Alberta Court of Queen’s Bench.
Bourassa v. Ryan and Ryan (Calgary; June 27, 1997; Power, J.)
There was an award of $45,000.00 in General Damages and $141,947.00 in economic losses in a case without any vehicle damage, updated to 2009 is $62,945.00 and $198,554.00 respectively.
Buchanan v. Wassef (Edmonton; October 16, 1996; Perras, J.)
There was an award of $50,000.00 in General Damages and $218,770.00 in economic losses (updated to 2009 is $70,373.00 and $307,910.00 respectively), with only $165.00 damage to the Plaintiff’s car.
Clearly, vehicle damage should be looked at as one piece of evidence in the overall picture, but not the deciding factor as to whether the Plaintiff was injured or not.
There are three main assumptions in any defence bio-mechanical engineer’s report which have now been refuted by modern studies. Those refutable assumptions are:
1. Vehicle damage is related to injury potential;
2. There is a reliable relationship between delta V (change in velocity of target vehicle) and occupant acceleration;
3. There is a minimum threshold of force necessary to cause various injuries.
Assumption number one that vehicle damage is related to injury potential was refuted by a recent paper in Farmer et al, I.I.H.S. (1998); September, wherein Farmer studied rear-end collisions in thirty-seven U.S.A. states for head restraint type versus injury. The authors found, in the largest study ever, that 44% of women and 34% of men were injured in crashes with less than one thousand dollars in damage.
As well, another recent study presented by A.F. Tencer at the Cervical Spine Research Society’s twenty-seventh annual meeting on December 16-18, 1999, looked at twenty-three crashes with little or no vehicle damage from a rear impact collision. They found that 27% had neck pain only; 46% had neck and low back pain; and 21% had neck and arm pain, some disc herniations verified by MRI.
Regarding assumption number two, that there is a reliable relationship between delta V and occupant acceleration, the seminal work in this area came out of Vancouver, B.C. Incredibly, no one had ever thought of crash testing a bunch of people all at the same delta V to see what would happen. Siegmund, et al, crash tested fourty-two subjects at two delta V’s, 2.5 miles per hour and 5.0 miles per hour. Observed results at 5.0 mph equals a 6.7-12 g (this is the peak acceleration of the head of the occupant). Thus, this study demonstrated that it is impossible to accurately predict occupant acceleration even if delta V is known to the tenth of a mile per hour; therefore, delta V does not predict head acceleration.
The third assumption inherent in all defence bio-mechanical reports is that there is a minimum threshold of force necessary to cause various injuries. If it can be proven that significant injury can occur in some individuals at very low levels of force (lower than most no-property-damage crashes), then most defence bio-mechanical tests will become irrelevant. This is exactly what was found in a natural experiment that took place on the Rattler roller coaster in Texas between 1992 and 1993. Three hundred thousand subjects voluntarily underwent five g’s of peak head acceleration. The acceleration impulse was similar in magnitude and duration to that of a three to four mile per hour delta V rear-impact collision. Defence bio-mechanical engineers would hold that such a change in delta V is not enough to cause injury. This study, however, found 656 injuries to the neck and low back, with thirty-nine significant injuries including twenty-eight cervical disc herniations, with 54% requiring surgery close to the time of the injury, and another 14% with surgery later; nine lumbar disc herniations, five spinal fractures, one case of temporary quadriplegia, and one case of permanent partial quadriplegia. The injured people were mostly female (77%) and of a considerably older age than uninjured subjects (thirty-seven).
The study illustrates two important points:
1. While small, there exists a real and validated risk of serious injury at relatively low levels of acceleration;
2. While the injury level was quite low (7,000 riders), the fact that these serious injuries do occur at such low levels of acceleration makes it impossible to rule out serious spine injury on the basis that the crash energy was too low to cause injury.
Publication of this paper by Spine effectively discredits any attempt by a bio-mechanist to claim that there is a minimum injury threshold for significant spinal injury. This makes all other testimony from such experts (minimal speed of impact, minimal acceleration forces), a call for the judge to improperly speculate that significant injury cannot result from low damage crashes.
If the defendant insurance company persists with this evidence your lawyer should bring a motion to strike the bio-mechanist’s report on the basis that your bio-mechanist’s attempt to assign an injury risk retrospectively is a classic example of “junk science” as risk in science is prospective. A probability can only be used as a prospective tool for populations – they cannot be used to rewrite history. In other words, the average value for a population does not allow for any inference to an individual member of that population, as random variation tells us that the individual can land anywhere on a probability curve. Put more bluntly, stating that the average person won’t be hurt in a crash and, therefore, the Plaintiff wasn’t hurt, is no different than stating that the average person weighs 170 pounds; therefore, no one can weigh 110 pounds.
Rare outcomes don’t occur very often, but they do occur, and it is illogical to state that something didn’t happen because it wasn’t likely to happen.