MYTHS/ JUNK SCIENCE FACTS
Witness: Sir Isaac Newton (1643-1727)
PRIMARY Fact 1: A Human Injury occurs in a motor vehicle collision – or in any blunt or sharp force traumatic event – when individual human tissues (with there own particular properties) are forced to move out of their own, individual, elastic ranges into non-elastic or plastic (non-returning) ranges. In a motor vehicle collision, forced occupant movement is required to create traumatic injury. The overall effect on tissue of forced movement is stretching and tearing of the tissue.
Fact 2: The elastic ranges of individual tissues are highly subjective, and do vary substantially Between – and Within – human individuals. Because of large human individual differences, a trivial perturbation and forced tissue movement in one person may cause stretching/and/or tearing to similar tissue in another person.
Fact 3: Human injury potential is not equivalent to the size or nature of the damages to the struck vehicle, the striking vehicles, property, or any other non-human matter. Human occupant injury potential or likelihood in a motor vehicle collision is instead directly related to the level of displacement of adjacent tissues that are forcibly moved in different directions with respect to each other.
Fact 4: The instantaneous acceleration/ deceleration suddenly applied to vehicles in collisions typically occurs in a duration of 0.1 seconds to 0.15 seconds and over a linear distance of only 6 inches. The struck vehicle’s entire change of velocity occurs within that short time and distance. Impulse in this short of time is technically referred to as "jerk" (i.e., the rate of change of acceleration).
Fact 5: There is no Mason-Dixon line at Delta V = 5 mph separating Injury from Non-Injury. While standard industry equations can easily yield the Delta V’s in this order of magnitude per the damage dimensions, there is more to the analysis than a “Gozinta Box” speed change equation.
Fact 6: Test crashes of vehicles dating back to research performed by Derwyn Severy at UCLA in the 1950's have demonstrated that in a motor vehicle collision, the head acceleration/ deceleration is two to five times that of the acceleration/ deceleration of the vehicle.
Fact 7: In a collision, the pre-collision kinetic energy possessed by a striking vehicle can be applied to the struck vehicle in various forms. These include translation (i.e., forced motion) of the struck vehicle, crush damage, heat, and others. The more strain damage that the struck vehicle experiences in a collision, the less transferred kinetic energy will be applied to (injury-causing) forced motions of the struck vehicle – and vice versa.
This point is illustrated by the SAE 970494 paper entitled “Lack of Relationship Between Vehicle Damage and Occupant Injury”, in which author Malcolm C. Robbins stated the following:
“A common misconception formulated is that the amount of vehicle damage due to a collision, offers a direct correlation to the degree of occupant injury. This paper explores this concept and why it is false reasoning. Explanations with supporting data are set forth to show how minor vehicle damage can escalate or even be the major contributing factor to occupant injury.”
Thus, the more damage (i.e., strain) that a vehicle shows, the less kinetic energy that is available to be applied to abruptly forcing the movement of the struck vehicle. In fact, it is forced movement that causes injuries to occupants. Small damage to a vehicle does not necessarily mean No Injury. Large damage does not necessitate Injury.
Fact 8: Human injury potential in a motor vehicle collision does, in fact, correlate with the instantaneous speed change of a struck vehicle (i.e., the target Delta V). However, the correlations is not 100% (i.e., 1.00 or perfect) – as has been traditionally inferred by the No-Injury-Possible – to anyone – oft-used, blanket, generic opinions and metaphors. In fact, injury potential is instead directly related to the individual human forced movements, the magnitude of accelerations/ decelerations, and the non-elastic displacement of the occupant’s individual body members — and not the size or nature of the damage to his or other vehicles.
Fact 9: Measured everyday life accelerations/ decelerations are not substantially similar to motor vehicle accelerations/ decelerations in their movements, levels of awareness, points of physical application, situation, duration, and direction.
Fact 10: The large volumes of so-called “Biomechanical” threshold data and numerous experimental results based on staged collisions with human volunteers seen in publications are of no direct relevance or validity to this – or any other – real world collision – where there are unlike human occupants, unlike medical histories, unlike vehicles, unlike durations, full awareness, and unlike circumstances. As I have stated frequently over the years, the nature of specific so-called “Biomechanical” research results from staged collisions -- with massive inherent experimental and methodological problems, full or partial awareness, protected human occupant subjects, a lack of face validity, and the complete lack of statistical significance -- eliminate any possibility that the research results can be extrapolated to the human population involved in real-world collisions.
Issues that are particularly significant that preclude staged collision data from being directly applied to human injuries in a real world collision include the following:
a. Staged collision results and data are often based on tests performed under laboratory conditions with extensive instrumentation attached to subjects. In these staged collisions, the human volunteer subjects have complete awareness of the impending experimental collisions. The researchers have the volunteer's permission to use them as live crash test dummies. The motivations of these volunteers varies. In some cases, the volunteers have offered their services in order to demonstrate how they can withstand a collision's effects. Clearly, no reasonable individual will deliberately volunteer for participation in an experiment in order to be seriously injured. In the real world, there is often limited or no awareness of the impending collision on a relaxed occupant, with surprise and panic resulting. The body motions of a braced individual are entirely unlike that of a relaxed, non-expecting, individual.
b. Staged collision results and data are often based on unrealistic and unlike collision circumstances. To avoid the possibility of injuring volunteer subjects in staged collision experiments, Biomechanics researchers must greatly limit the collision speeds and associated forces applied to human subjects.
c. Staged collision results and data are often based on the use of cadavers, synthetic crash test dummies, live farm animals, and denuded human tissues in unrealistic tissue environments. These are not realistic human subjects, and have no face validity.
d. Staged collision results and data are often based on inappropriate and unlike human subjects' body sizes, ages, genders, nationalities, physical features, pre-collision positions, etc. in the experiments.
e. Staged collision results and data are virtually always based on inappropriate or unlike vehicles with different component properties selected for the experiments.
f. Staged collision results and data are often based on inappropriate or unlike exterior and environmental factors in the staged experimental collisions.
Therefore, as stated above, it is unreasonable and altogether incorrect to extrapolate the results from generic, flawed, non-statistically significant crash experiments conducted in very restricted and unlike staged collisions to highly specific, complex, real-world collisions with unlike vehicles, unlike circumstances, and unlike occupants. In fact, it is inappropriate and incorrect to cite any studies and/or force analogies or events that are not substantially similar to the actual subject acute-angle collision experienced by the occupant. Any conclusions regarding injury causation – or lack of which – based on these staged collision analogies lack merit.
Fact 11: The National Accident Sampling System (NASS) database compiled by the unbiased Department of Transportation, National Highway Traffic Safety Administration over a 16 year period that at Delta V’s of 0 to 5 mph, 42.14% of the 2598 occupants in collisions at these Delta V’s had recorded had either Minor, Moderate, Serious, injuries (AIS 1 to AIS 3). At Delta V’s of 6 to 10 mph, 65.45% of the 25,202 occupants in collisions at these Delta V’s recorded either Minor, Moderate, Serious, Severe, Critical, or Fatal injuries (AIS 1 to AIS 6).
Fact 12: The actual human variables that can affect the size of the elastic ranges of a human occupant's body members are:
c. Anthropometrics (i.e., body dimensions and sizes)
e. Body type
f. Physical conditioning
g. Pre-collision body postures and positions
h. Pre-collision degrees of freedom of the body members (i.e., amount of physical movement possible)
I. Pre-collision symmetry or asymmetry of the occupant's body members
j. Existing pre-collision diseases or injuries that are either symptomatic or asymptomatic
k. Present state of mind, individual psychological and behavioral factors, individual factors affect physiologic functioning (e.g., smoking, drinking, drugs, anger, etc.)
l. Expectation of collision
In a motor vehicle collision, there are also vehicular variables present at the time of the collision which can affect the kinematics (i.e., body motions) generated in the collision. For a given speed and geometry of a motor vehicle collision, the vehicular variables that influence the occupant body kinematics (i.e., motions) at the instant of collision and the probability of an occupant experiencing an injury are also affected by the vehicular variables:
m. The geometric design and physical configuration of the interior and exterior of the vehicle.
n. The selected materials, and the mechanical and structural features of the interior and exterior of the vehicle.
o. The condition and properties of the vehicle's energy management system.
Fact 13: One cannot automatically rule out -- or automatically assume-- occupant injury because of the amount of vehicle damage. Instead, motor vehicle collisions and the associated occupants’ injuries must be evaluated on an individual basis with respect to the inherent geometry of the collision itself, the individual characteristics of the human occupants, the design, condition, and strength of the vehicles, and the nature of the collision environment.
Fact 14: Determining the likelihood of injuries in motor vehicle collisions, and in particular, low-speed motor vehicle collisions, is a complex, individualized consideration. Blanket opinions on injury causation that are the same for all humans across all individual differences are not valid. It is, therefore, inappropriate to make simplistic blanket generalizations that relate vehicle occupant injury potential to speed, vehicle crush damage, and costs to repair the property damage.
Fact 15: As compared to the general population, staged collisions use only a relatively few volunteer subjects to act as human crash test dummies. Compared to the individual difference of humans in the world’s population, the sample size of volunteers in these staged collision test is indeed below microscopic. In fact, the population at large was not involved in the stated crash tests. It is therefore not possible to be able to state statistically significant opinions regarding Injury v. Non-Injury for a given perturbation or Delta V that can be universally applied to the population at large.
Fact 16: The occupant’s awareness of an impending impact is a significant variable in affecting injury vulnerability. Some researchers of staged test collisions have attempted to have volunteer crash occupants be unaware as possible of the impending impact. However, the fact that these volunteer crash occupants have knowingly arrived at the crash location, and placed in test vehicles to be involved in impending crashes – often to be wired to accelerometers and other instrumentation – creates awareness. It is therefore impossible to eliminate awareness and the intentional and/or instinctive bracing that occurs. The awareness biases the results of these test crashes. These staged collisions are, therefore, not substantially similar to actual real-world collisions, and the results cannot be directly extrapolated to similar real-world collisions.
Fact 17: There were more than 1500 injuries on amusement park rides in 2015 – most due to rides on roller coasters and bumper cars. The fact is that the mere existence of bumper car rides does not immediately necessitate that they are perfectly safe for everyone at all ages, with all body types, in all life circumstances, and in all types and directions of bumper car collisions as seen in fallacious comparisons of the subject collision to bumper cars.
In the oft-quoted bumper car test crash study – including a total of 10 bumper car impacts – conducted by Gunter P. Sigmund et al. and published in a paper entitled “Speed Change (Delta V) of Amusement Park Bumper Cars” (1999), Sigmund found that the maximum Delta V of the typical 10 bumper car collisions was 5.25 mph (7.7 kilometers/ hour) – indicating that the other nine Delta Vs in the bumper car study collisions were lower than 5.25 mph. It turned out that one of the bumper car collisions was unmanned, and only nine of the 10 collisions actually had Delta V data obtained. As stated, the maximum Delta V of the collisions with was 5.25 mph, but the minimum was only 3.62 mph (5.83 kph), with a mean at 4.34 mph (6.99 kph). Notably, this bumper car crash test experiment utilized a grand total of two athletic males – 25 years old, 5'11" tall and 155 pounds and 32 years old, 6'1" tall, and 200 pounds. It was not entirely surprising that neither male athlete was injured in the 9 manned experimental bumper car collisions.
However, this result hardly makes it possible to extrapolate the results of bumper car collisions with two athletic males with awareness as being perfectly safe for the population at large – as has been done here after the fact. To the author Sigmund’s credit, he did state “... Both occupants were male adults, physically fit, active in outdoor sports and do not necessarily represent the general population.” That would be correct. Unfortunately, the results of this study have been aggressively and fallaciously extrapolated to suggest that collisions in bumper cars are trivial and 100% safe, and that collisions with Delta V equal to or below 5.25 mph cannot produce injury to anyone.
As stated above, what is safe and trivial to one particular population of humans and body-types may not necessarily be safe to all humans. Clearly the vast majority of populations of riders of bumper cars are young, aggressive, and pliable. And notably, most amusement park ride injuries reportedly occur on either roller coasters or bumper cars, and there has been litigation on injuries occurring on roller coasters and bumper cars. Over the years, it is noted that many bumper car operators have tried to reduce the numbers of collision-related injuries by requiring all of the cars to travel in the same circular direction. However, the fact is that several bumper cars amusements in theme parks have simply given up their permanent bumper car rides because of the risk of liability. Several have been shut down in recent years – including the recent Dodge City Bumper Cars at Six Flags Over Georgia. If they were actually perfectly safe to all people, all bumper car amusements would still exist everywhere.
1. MYTH: NO DAMAGE = NO INJURY
Little or No Vehicle Property Damage on a struck motor vehicle means that no human injury Is possible -- to anyone.
2. MYTH: BELOW 5 MPH DELTA V = NO INJURY
If the Delta V of a struck vehicle in a motor vehicle collision is calculated to fall below 5 mph, that means that no human injury is possible -- to anyone.
3. MYTH: HUMAN VOLUNTEERS NOT INJURED IN STAGED COLLISIONS = NO INJURY
Staged test collisions conducted with human volunteers who were not injured means that no human injury is possible at similar speed changes in an actual motor vehicle collision -- to anyone.
4. MYTH: G'S LESS THAN ON ROLLER COASTERS = NO INJURY
In collsions where the G's are calculated to fall below those found in amusement park roller coasters (in particular 6.3 G's -- the maximum G's in the worlds most extreme roller coaster, "Tower of Terror" located in Gold Reef City, South Africa), then no human injury is possible at 6.3 G's or less in a motor vehicle collision -- to anyone.
5. MYTH: DELTA V LESS THAN IN BUMPER CARS = NO INJURY
In a collision where the Delta V is calculated to fall below 5.25 mph, (the maximum Delta V occurring in 9 amusement part bumper car test collisions with two adult male athlete occupants (1993)), then no human injury is possible at that or lesser Delta V -- to anyone.
6. MYTH: G's LESS THAN G's IN EVERYDAY LIFE = NO INJURY
The G's in a subject motor vehicle collision are less than those found in everyday life -- including the G's in a sneeze, stepping off a curb, a back slap, turning to the side, a chair plop, and others -- and with spine forces less than bending over and tying your shoes. Therefore, no human injury is possible -- to anyone.
7. MYTH: LOW DAMAGE = NO OCCUPANT MOVEMENT CAN OCCUR
Because a subject collision occurred at a low speed, there could have been no occupant movement, and no human injury was possible -- to anyone. (See Thomas Szabo video of 1,2,3,4,5 mph Delta V's).
8. MYTH: LOW DAMAGE = THERE IS NO MECHANISM OF INJURY
Because a subject collision occurred at a low speed, there was no mechanism of injury in tension, compression, torsion, shear, flexion, extension, and bending -- to anyone. Therefore, no human injury was possible -- to anyone. (See Thomas Szabo video of 1,2,3,4,5 mph Delta V's).
John E. Baker, Ph.D., P.E.