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Posted on 05-28-2013

Bullet vs. Target Vehicles in Auto Accidents

I've spoken to many friends and family members who have been involved in auto accidents in Baltimore. Some have accidentally caused the collision (the bullet vehicle) while others have been on the receiving end (target vehicle).  Almost universally those causing the crash end up saying "there's no way that person could be hurt! I barely hit them!" On one hand they are likely concerned about their auto insurance rates rising as a result of a faulted motor vehicle collision, but on the other hand, they really can't imagine the passenger's in the other car being injured given the fact that they feel ok after the crash.

Dr. Arthur Croft sheds some light on this phenomenon in his book "Whiplash and Mild Traumatic Brain Injuries: A Guide for Patients and Practitioners." His institute, the Spine Research Institute of San Diego, was the first to conduct an experiment that examined the difference between the forces experienced in a frontal crash (the bullet vehicle) and a rear-end impact (the target vehicle).

In his research he determined that the forces on the human subject's necks were up to 4 times higher in the rear-ended vehicle than in the front impact vehicle. He also noted that subjects felt more of an impact when they were in the rear-ended vehicle than if they were in the bullet vehicle.

One major explanation as to why this is the case deals with preparation. The front-end impacted vehicle (bullet vehicle) typically can see the accident unfolding in front of them, allowing for even minor "bracing" in preparation which leads to less injury as compared to the unaware target vehicle's occupants.

More interestingly the spinal kinematics are different between the striking and struck vehicle. In the bullet vehicle the driver experiences a "monophasic" response, in which he experiences a single forward bending motion as he is restrained by the seat belt and shoulder harness.

The target (rear-ended) vehicle's occupants actually undergo a "biphasic" response. First, the seat back strikes the occupant from the rear, causing the curves of the spine to flatten. Then the pelvis and torso are accelerated forward by the seat, leaving the head momentarily at rest, causing the head to lag behind slightly before striking the head restraint. Once it strikes the head restraint, the head actually accelerates quicker than the rest of the body forcing it to rebound faster, and accelerate at a greater magnitude than that of the car or the pelvis or the torso. Then in the second phase, the occupants must actively resist forward motion aided by the seat belt by decelerating their forward head and body movement.

Dr. Croft's mathematical analysis in the rear-ended vehicle is quite striking. He notes that if the rear-ended (target) occupant's head were to be extended over a table she would feel the acceleration of 1g (earth's gravity). Given that the average human head weighs 8-10 lbs, with a peak acceleration noted to be around 13g during a rear-end impact, it is the equivalent of a human head effectively effectively weighing between 102-128 lbs in a matter of 2 tenths of a second! Even knowing that a rear-end impact was pending (which most real-life occupants do not know) they CAN NOT under any circumstances actively brace themselves to prevent this level of acceleration in their necks.

Hence, it is clear that rear-ended occupants can and do experience more force in their spines than do the individuals in the car causing the collision in a front-end collision.

If you or anyone you know has been involved in an auto accident in Baltimore or the surrounding areas please contact Mid-Atlantic Spinal Rehab & Chiropractic at (443) 842-5500. Dr. Gulitz is a Baltimore Chiropractor specifically trained in the rehabilitation of auto accidents including whiplash and mild traumatic brain injuries.

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