Even though cars get a little safer each year, and fatality rates are declining, car crashes are still one of the leading causes of death and injury in the United States. One of the reasons cars have been getting safer is because of a well-established testing program.
Crash Test Dummies
The dummy's job is to simulate a human being during a crash, while collecting data that would not be possible to collect from a human occupant. All frontal crash tests in the United States are conducted using by the Hybrid III dummy. This guarantees consistent results. A dummy is built from materials that mimic the physiology of the human body. For example, it has a spine made from alternating layers of metal discs and rubber pads. The dummies come in different sizes and they are referred to by percentile and gender. For example, the fiftieth-percentile male dummy represents the median sized male -- it is bigger than half the male population and smaller than the other half. This is the dummy most commonly used in crash testing. It weighs 170 lbs (77 kg) and is 70 inches (5 ft 10 inches or 1.78 m) tall.
The dummies contain three types of instrumentation:
1-Accelerometers, These devices measure the acceleration in a particular direction. This data can be used to determine the probability of injury. Acceleration is the rate at which speed changes. For example, if you bang your head into a brick wall, the speed of your head changes very quickly (which can hurt!). But, if you bang your head into a pillow, the speed of your head changes more slowly as the pillow crushes (and it doesn't hurt!).
The crash-test dummy has accelerometers all over it. Inside the dummy's head, there is an accelerometer that measures the acceleration in all three directions (fore-aft, up-down, left-right). There are also accelerometers in the chest, pelvis, legs, feet and other parts of the body.
2-Load sensors, inside the dummy are load sensors that measure the amount of force on different body parts during a crash.
3-Motion sensors, these sensors are used in the dummy's chest. They measure how much the chest deflects during a crash.
Crash test types
The National Highway Traffic Safety Administration (NHTSA) conducts two types of crash tests as part of the New Car Assessment Program.
* 35-mph frontal impact - At 35 mph (56 kph), the car runs straight into a solid concrete barrier. This is equivalent to a car moving at 35 mph hitting another car of comparable weight moving at 35 mph.
* 35-mph side impact - A 3,015-pound (1,368-kg) sled with a deformable "bumper" runs into the side of the test vehicle. The sled's tires are angled. The test simulates a car that is crossing an intersection being sideswiped by a car running a red light. The sled actually moves at 38.5 mph, but when you do the math, it is equivalent to a 35-mph side impact because of the way the wheels on the sled are angled.
The "Perfect" Crash
Obviously, the ideal crash would be no crash at all. But, let's assume you are going to crash, and that you want the best possible chances of survival. How can all of the safety systems come together to give you the smoothest crash possible?
Surviving a crash is all about kinetic energy. When your body is moving at 35 mph (56 kph), it has a certain amount of kinetic energy. After the crash, when you come to a complete stop, you will have zero kinetic energy. To minimize risk of injury, you would like to remove the kinetic energy as slowly and evenly as possible. Some of the safety systems in your car help do this.
Ideally, your car has seatbelt pretensioners and force limiters; they both tighten up the seatbelts very soon after your car hits the barrier, but before the airbag deploys. The seatbelt can then absorb some of your energy as you move forward towards the airbag. Milliseconds later, the force in the seatbelt holding you back would start to hurt you, so the force limiters kick in now, making sure the force in the seatbelts doesn't get too high.
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