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Safety features in cars

Discern the definitions of systems that help you handle the unforeseen. Here's a look at the current range of passive car safety features available.

It was about 50 years ago when Newton's First Law of Motion began to be seriously considered by the automobile industry. The law? In part, it states that an object in motion tends to stay in motion – unless acted upon by an outside force. Over the course of the last half-century, great scientific research has focused on dispersing kinetic energy in a crash. The effort has yielded such standard car safety features as seat belts, collapsible steering columns, shoulder belts with emergency-locking retractors, airbags, unibody crush zones and other features that provide an even higher level of protection. Here's a look at the current range of passive safety features in cars.

What they are: There was a time when crude steel bumpers were the sum total of automotive crash engineering. Found outside or inside of front and rear body fascias, today's lightweight, sophisticated bumpers may be attached to the unibody on metal tubes or struts and may have shock-absorbing features such as foam lining, deformable brackets or other energy absorbers. 

How they work: By cushioning the force of a minor impact, bumpers can help prevent more costly damage to the vehicle bodywork and structure.

How they benefit the passengers: Bumpers are designed to help reduce vehicle damage in a minor collision. They also function as part of the vehicle's overall crash energy attenuation engineering. By collapsing in moderate to severe collisions, bumpers sacrifice themselves to help protect the vehicle's occupants.

Crumple zones
What they are: Unibody passenger vehicles and many body-on-frame vehicles utilize specially designed front and rear areas that crumple or deform in a collision, helping to disperse energy. 

How they work: A passenger vehicle's unibody is made of different sections of steel (or sometimes aluminum) welded into a single monocoque or unibody structure. Designed on computers and proven in the laboratory, special areas at the front and back of the unibody are specifically designed to bend, fold or otherwise deform in an accident. Body-on-frame vehicles often use a similar strategy in their body structures.

How they benefit the passengers: Crumple zones help slow the rate of deceleration for passengers, helping to reduce the chances of injury.

Frontal airbags
What they are: Frontal airbags are inflatable cushions (bags of inert gas) that help slow the rate of deceleration for the driver and front passenger during a frontal collision. 

How they work: The driver’s and front passenger's airbags are stored in compartments in the steering wheel and instrument panel, respectively. In a collision that exceeds a preset level of forward deceleration (determined by crash sensors located in the vehicle), a pyrotechnic gas generator is ignited and, in a few milliseconds, generates nitrogen gas that deploys and fills the airbag. By the time the occupants have moved forward toward the airbag, it is ready to cushion them.

The latest frontal airbags have dual-rate inflators that deploy at different rates depending on the severity of the crash – faster deployment for high-speed impacts and slower deployment for low-speed crashes. In addition, some systems are sophisticated enough to differentiate between large and small passengers and adjust their deployment rate to suit. Some airbags have a two-chamber design that helps keep the passenger centered during an accident.

How they benefit the passengers: It is important to note that frontal airbags are not a replacement for seat belts. When used in conjunction with seat belts, however, they have been shown to help reduce the severity of injuries in frontal accidents.

Side airbags
What they are: Located in the side bolsters of the driver's and front passenger's seats, side airbags deploy during certain side impacts to help provide protection for the thorax. 

How they work: As with frontal airbags, side-impact airbags deploy when side-impact sensors trigger an electrical circuit to ignite a gas generator. In just milliseconds the side airbags inflate forward from the outside of the seats.

How they benefit the passengers: Side airbags help reduce driver and front-passenger thorax injuries in a side impact. The reason is because the sides of a vehicle offer a much smaller deformable area than the "crumple zones" (see below) in the front and rear of a vehicle.

Side curtain airbags
What they are: The natural complement to side airbags, side curtain airbags help protect the heads of the driver and outboard passengers in certain side impacts. They are hidden above the headliner, directly above the side windows. 

How they work: As with frontal and side airbags, curtain side airbags deploy when side-impact sensors trigger an electrical circuit to ignite a gas generator. As they inflate, the side curtain airbags descend from the headliner to help offer a protective curtain covering the side windows.

How they benefit the passengers: Head injuries are among the most traumatic kinds of injuries that a person can sustain. Side curtain airbags help provide a potentially lifesaving layer of protection between the occupant's head and the side pillar of the car, or an object outside of the car.

Belt systems
What they are: Seat belts, including shoulder harnesses, are the first line of defense against injury in an automobile accident. Manufactured from strong synthetic webbing, they help hold wearers in place during a collision, helping to control their rate of deceleration. All outboard seating positions on new vehicles feature seat belts that are integral with shoulder harnesses (although some center belts on bench seats do not). 

How they work: A surprising number of technologies have improved seat belt design since their inception many years ago. Emergency Locking Retractors (ELR) allow the wearer freedom of movement while driving, but lock the seat belt in place in a collision. Automatic Locking Retractors (ALR) allow manual locking of the seat belt to secure a child seat. Pretensioners use a pyrotechnic device to pull the seat belt tight immediately following a collision. And force limiters allow the seat belt to "stretch" during a collision to more gradually decelerate the wearer.

How they benefit the passengers: The seat belt's first and most important task is to keep the wearer in place during a collision, helping reduce the chance that he or she will be ejected from the vehicle or strike other occupants or injurious surfaces inside the car. Technologies like pretensioners and force limiters enhance the seat belt’s ability to control the wearer's rate of deceleration in an accident.

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