Seat belts reduce the risk of death and serious injury by 50 percent, but when improperly worn, the seat belt can cause significant injury in the event of a collision. When driving in your car, you have built up motion, or ‘kinetic energy’. When you want to stop, you use the brakes which then converts all this kinetic energy into heat as the brake pads grind you to a stop.
In a crash, rather than the brakes absorbing all this energy, impact on the vehicle and your body absorb it instead. During this collision, inertia continues to throw your body forward, but is only prevented by the seat belt. Consider driving at 30 mph. In the event of a frontal collision, that will be 44 feet per second coming to a complete stop in under one second. That’s a lot of energy for your body to absorb against a thin strip of fabric and so it’s essential that you wear a seat belt properly.
What is the Proper Way to Wear a Seat Belt?
When putting on your seat belt, you should avoid:
Twisted Seat Belts
Before you fasten your seat belt, ensure that there are no twists in the belt 
. Seat belts consist of a wide thin woven material called webbing. Due to the strap being wide, during a frontal collision it helps to transfer the pressure exerted from your body against the belt over a wider area. If the belt is twisted, this area becomes much narrower which can result in the belt cutting into the body.
To give you an idea and an analogy of how much pressure your body exerts on a seat belt during a frontal collision at 30 mph, it’s roughly equivalent to falling from a height of 30 feet (9.1 metres). Ensure the seat belt remains flat against your body 
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Badly Positioned Seat Belts
Due to the pressure of the body onto the belt during an impact, it’s important to protect internal organs. The lap belt 
should be placed over the pelvic region and not across the abdomen.
The thin edge of the belt can easily slice into skin. To avoid neck injury, the diagonal strap should rest over the shoulder and not the neck 
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Incorrectly Fitted Seat Belts
Some people ask ‘can you wear a seat belt under your arm?’ The issue here is that it then places the belt across the ribs, which contain internal organs. Although seat belts save lives, they can also cause injury. A properly worn seat belt over the shoulder can potentially result in a broken collar bone after a collision. But if it’s worn under the arm 
, injury may result in broken ribs and damage to internal organs.