According to the National Safety Council, over 40% of all car accidents are rear-end collisions. One of the most dangerous elements of a rear-end collision is the unexpected nature of the accident. The driver of the front car is caught totally by surprise and is unable to take any protective measures, such as bracing themselves for the impact.
In addition to damage to the car, the impact of a rear-end collision can cause permanent injury. The mass of a vehicle, multiplied by speed, determines the amount of force applied to the car being hit. Most vehicles are rear-ended while at a complete stop, absorbing the full force of an impact. The larger the vehicle or the approaching speed, the greater the force of collision. Rear-end collisions involving trucks or speeding cars can be fatal. In just the past month, the Missouri State Highway Patrol reported 45 fatalities in car accidents.
That brings us to the science behind the rear-end collision. It requires looking at g-force, inertia, force, mass, and speed.
From a general standpoint, a rear-end accident involving two average cars with the back car traveling at 40 mph is the equivalent of the front car hitting a brick wall at 20 mph.
“G force” is defined as the acceleration imposed by earth’s gravity, or 32.2 feet per second, squared. A force of 5G, for example, means that a body is accelerating at five times the force of gravity. One researcher has described the effect of acceleration to injuries of the neck:
“If, as a result of an accident, the head accelerates in relationship to the trunk -backward, forward, or sideways -injury to the neck may result. Because lesions produced in this way differ from those resulting from forced passive movements of the head, it seems worthwhile to differentiate them by the term acceleration injuries of the neck. In acceleration injuries, the force applied to the neck is roughly equivalent to the weight of the head multiplied by the speed that the head is moving”.
The human head has an average weight of 10 pounds. Consequently, a 5G force results in a potential loading of approximately 50 pounds to the head.
West, Gough, and Harper found that at just 7.25 mph, vehicle peak acceleration was 3.1 G, while the occupant’s head accelerated in the forward at a force of 8.3G. This is equivalent to an 83-pound force acting on the head. Forward acceleration of the cervical spine will result in multiple-plane loading components, creating a shearing force, tensile force, and a compressive or axial force.
Working on cadavers, researched performed ligament uniaxial tension testing on C2-C7. They found that the anterior longitudinal ligament had a mean ultimate load of approximately 30 pounds. Furthermore, according to the Society of Automotive Engineers, the limit on shearing force in the cervical spine is 231 Newtons, or approximately 52 pounds, and the limit on axial force for the upper cervical spine is 249 Newtons, or approximately 56 pounds. One Newton is equal to 0.225 pounds of force. Their calculations also demonstrated that cervical injury could be incurred, reaching loadings of 190 pounds of torque, at speeds as low as 7.5 mph in an untensed neck of a normal, healthy individual.
Similarly, researchers observed that the risk of injury appears to be greatest in collisions with impact velocities between eight and 20 mph. They also concluded that the force to the head can reach 100 pounds in collisions where speed at impact is even less than 15 mph.
Another group of researchers observed that tolerance levels may be even more restricted in individuals with prior health problems:
“Consider a person with a prior neck problem such that his or her natural neck extension is limited to only 20 degrees and damage level is only 70 lbs, due to scar tissue. With only a small initial tensing of the neck muscles, this damage level will be reached at a push speed of 2.5-3.0 mph! Note that the lower push speed range is similar to or even lower than the speeds typical for causing vehicle damage. Thus, human body damage can occur with either 0 or very small amounts of vehicle damage and it is not necessary to have copious vehicle damage in order to hurt the human body”.
The injuries sustained in accidents can have long-term consequences. Hohl, a physician researcher, studied 146 patients, with no pre-existing cervical degenerative changes, who had sustained soft-tissue injuries resulting from automobile accidents. He concluded, after a five-year study period, that 39 percent of the patients showed degenerative changes.
Without even considering high-speed rear-end collisions, researchers have found that the physics of low-speed rear-end collisions are significant and easily cause serious injury to the victim of a rear-end car accident. Obviously, the faster the car that rear-ends a victim, then the more traumatic the injury.
After being involved in a rear-end collision, it is important to contact an experienced auto accident attorney who understands the physics behind what has happened to an accident victim. The more an attorney understands about a situation and what has happened to their client, the more effectively the attorney can represent victims and get them the compensation they deserve.