Thousands of automobile collisions occur everyday. And every day thousands are injured. Researchers note that the majority of accident injury claims occur at relatively low speeds of about 12 mph.
This causes tremendous disputes between injured parties and the insurance companies that are responsible for compensating them fro their injuries. To insurers, there really is no speed at which they want to admit and injury could occur. For economic reasons they try to dismiss whiplash in its entirety as if it does not exist.
Thanks to recent irrefutable research studies proving the existence and exact mechanism of whiplash injuries, insurers are hard pressed to try the "whiplash is a hoax" defense nearly as much as in the past.
A more recent tactic is to claim the speed of the collision is too low to cause injury. The defense often relies on their insured's reports of how fast they were going when they ran into the back of the other party-obviously biased data. Other times photographs of the vehicle damage is used to show a low speed. Often, the photographs are shown to an Accident Reconstructionist who by merely looking at photographic damage renders an opinion on how fast the vehicles were traveling. They will even go so far to make statements such as "the evidence suggests there was insufficient force to cause human bodily injury …" This would be laughable if it did not cause so many problems for injured victims.
Here are but a few facts concerning motor vehicle injuries and their relationship to speed with supporting scientific evidence.
Three different studies (Panjabi, Panjabi and Cholewicki and Kaneoka) proved the mechanism by which the neck is injured by a rear impact force. , ,  The studies involved simulating a rear impact collision ot live human test subjects and recording the results with cineradiography (high speed motion x-rays). The researchers found that the neck was injured by deforming into an "S- shaped" configuration. All three of these studies found that this physical event occurred at speeds as low as 2.5 mph.
The radiographically proven human threshold for injury in a rear impact collision therefore is 2.5 mph. Other authors have disputed these figures and some insurance company sponsored studies have found the threshold to be closer to 5 mph.
For the sake of argument, let's stipulate that the 5 mph threshold is correct. It still means that a collision of only 5 mph can cause damage to the neck.
Freeman et. al. in Spine, Vol. 23, Number 9, 1998, p. 1046 shows the damage thresholds for many cars. This is the minimum speed required to cause the car to show visible signs of damage. The smallest, lightest vehicle listed was the 1980 Toyota Tercel, which required a collision of 8.1 mph to become damaged. On the other end of the spectrum was the 1989 Chevrolet Citation, which required 12.7 mph. A Ford F-250 pick up required 11.7 mph.
Cars built today are equipped with rear bumpers designed not to show any damage below 5 mph. In an attempt to reduce repair costs shouldered by insurance companies, crash standards were adopted to mandate rear bumpers must withstand a 5 mph collision into a fixed barrier (wall, pole, etc) without any visible evidence of damage. It should be noted that this standard involves testing of "vehicle to barrier" crashes not "vehicle to vehicle" testing.
In "vehicle to vehicle" crashes where the bumpers line up well, it takes considerably more force to cause visible bumper damage than a 5 mph collision. Some tests have shown that cars could be crashed repeatedly at 20 mph and not show outer damage. In a "vehicle to vehicle" crash it is estimated that the minimum speed to cause visible damage is approximately 15 mph.
Another consideration is that while a bumper may look undamaged from the outside after a collision, inside under the skin, the foam or plastic may be crushed or cracked. This is not seen from the outside, so photographs would make it appear as if no damage was sustained. Still further, the bumper may appear intact, but on unibody vehicles, the unibody may be bent or deformed by a collision. This may not be apparent and some auto repair facilities may miss it.
So what does this mean? It means that if you are rear-ended and your bumper is cracked, dented, or misplaced at all, your collision involved speeds in excess of 15 mph. That's 3 times the human threshold for injury if we use the 5 mph figure. In reality, the proven threshold is only 2.5 mph, so a collision of 15 mph is 6 times the threshold for injury.
Now let's say your vehicle sustained no visible damage, but your neck hurts after the collision. Does that mean you were not really injured? No. It means that the vehicle's threshold for damage was not exceeded. The impact could have been 10 mph. Too low for bumper damage, but still 4 times the threshold for human injury.
In a low speed collision, the kinetic forces that are transferred from the other vehicle into your vehicle are not dampened or bled off by your bumper. Instead, the force is transmitted through the vehicle, into your seat and to your neck resulting in injury. If your body or neck are jolted or jerked by the impact, an injury could occur.
Another aspect to consider is if your vehicle is moved forward by the impact. An average car weighs close to 4,000 lbs. Let's say you are hit from behind and your car is pushed forward a few feet, but shows no signs of bumper damage. Is it possible to be hurt? Yes, of course. The force required to move a stationary 4,000 lb object is tremendous. Can you walk up to a car sitting at a red light with its brakes on and shove it forward even an inch? Not likely. A collision that is strong enough to propel a car forward by even inches is plenty enough force to cause a whiplash injury.
So, as you have now learned, there really should not be any dispute on whether a low speed collision can cause injuries. It has been scientifically proven by several studies. It is also a fact that the speed required to cause bodily injury is quite low, a scant 2.5 mph. It has also been shown that any accident that causes damage to the rear bumper is likely to cause injuries and even in accidents where there is no outward physical damage to the vehicle, there may still be sufficient forces involved to cause bodily injuries.
Panjabi MM, Grauer JN (1997): "Whiplash produces a S-shape curvature of the neck with hyperextension at lower levels." Spine 22 (21): 2489-94.
Panjabi MM, Cholewicki J, Nibu K, Grauer JN, Babat LB, Dvorak J, Bar HF (1998-12-01): "[Biomechanics of whiplash injury]." Orthopade 1998 Dec; 27 (12): 813-9.
Koji Kaneoka, Koshiro Ono, Satoshi Inami and Koichiro Hayashi (99-04-15). "Motion analysis of cervical vertebrae during whiplash loading." Spine 24 (8): 763-770
Characteristics of Specific Automobile Bumpers in Low Velocity Impacts, SAE 940916