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Tuesday, September 4, 2012

Rear End Collisions and Injuries. It's Not What You Think!

Rear-End Collisions, Crumple Zones, and Injuries. 

For the purposes of simplicity, I'd rather skip over the details of Newton's laws of motion and try my hand at  quickly explaining with the use of a few images and facts, why its better to be fully stopped when someone rear-ends your car, rather than rolling forward.

One has to be aware of the way modern vehicles are manufactured.  They are made much different than the way they used to be made in the early days.  Nowadays, and actually for the last several decades, automobiles are made with crumple zones.  A crumple zone is part of the structure of vehicles that simply allows the metal to deform and bend.  The purpose of these crumple zones are to absorb energy from the impact.  To give you an example of the importance of a crumple zone in a vehicle, just think; if you for example, fall from a roof and land on a concrete floor, the chance of injury to your body would be much greater than if you fell from the same roof and landed on, say a very thick mattress.  This is due to the ability of the mattress to slow your body down by absorbing the energy of your falling body.

Look at the way the cars are deformed and will absorb the energy of the collision.

Here is another car.  Look at the way the hood folds up and practically acts like an accordion.  Again, its designed to absorb energy.

Here is a diagram of a car hitting a fixed object.  The crumple zones in a car are located in both the front and the back.

Now if you try to relate this concept to the impact of a car collision, it will begin to make sense why it is advantageous (in most cases) for your car to be completely stopped if you get rear ended.  It is difficult for some people to get this concept.  The mathematical brain is thinking mathematics.  "Okay, if I am traveling forward at about 10 miles per hour and get hit in the back by someone who is traveling at 20 miles per hour, you simply subtract 10 mph from 20 mph to get a net force on the back of my car of only 10 mph."  The thought process is 20 mph-10 mph = 10 mph impact which always sounds better than getting hit at 20 mph.  The math is correct.  You are only being hit at 10 mph.  But, in terms of shock and impact to the body, including the neck and head, during the rear end collision and whiplash, you are probably better to be standing still with your foot on the brake when you are hit from behind.  "But wait, you just told me a 10 mph hit is better than a 20 mph rear end hit?"   Here is the confusion.  Read on.

Okay, back to the crumple zones.  Remember, the crumple zones are designed to absorb energy.  They are designed to absorb energy that that would normally get transferred to the occupants of the vehicle.  So,  here are both scenarios; the first scenario is car rolling and second is car completely stopped: 

Scenario 1.  You are rolling forward 10 mph, you get hit from the back, your car's crumple zones do NOT have the chance or ability to fully absorb the impact of the other car hitting you.  Your car lunges forward from the impact, and your neck and head flies back in the seat as a result of the other car hitting you.

Scenario 2.  Your car is completely stopped, foot on the brake.  You are going 0 mph, and you get hit at 20 mph.  In this case, the crumple zones have a chance to do their job, which is to absorb the impact of the collision and reduce the forces upon the occupants of the vehicle getting hit.  Your car will (generally) not lunge forward as much if you were already rolling forward.

The other way I can explain this to you is for you to just look at the way race cars are made.  Have you ever seen a race car going 150+ mph that crashes into a wall or another car?   What does it do?  It comes apart.  Parts fly everywhere, including the wheels, which fly everywhere.  The purpose here is the same thing.  It's to absorb energy so that the driver of the car gets less of a shock to his body.  Of course, this is just a very simple way for me to explain how these car accident impacts cause injuries, and how the relative motion of the car paradoxically affects the injuries to the passengers.  I say, paradoxically, because it goes against ones rational thinking.  Just remember, crumple zones are your friend.  

A piece of advice to you:  If you think you are about to get get rear ended, good advice would be to firmly plant your foot on the brake and put your head against the head rest.  Let the cars absorb the impact, not your neck!  Also, call a chiropractor right away.

I treat these injuries all the time.  My address is 3161 Dykes Road in Miramar Florida. 33027. Dr. Alan Himmel. My Telephone Numbers are: 954-659-8600 and 305-979-5549. My Web address is: 

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