What Happens During a Car Crash?
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What Happens During a Car Crash?

Why are cars safer than ever before? From systems to prevent an accident from happening to structural design that deflects impact forces, there are a number of factors at play that help you survive accidents. Here’s why a front-end collision that would have been lethal a few decades ago will result in little more than a couple bruises today.


The Principle Behind Crash Safety

If the car strikes an object, the force stops it. However, inertia is still acting on the passengers inside, so they’re still moving at the same speed the car was pre-crash. Before safety was a factor in car design, these passengers would fly forward into the dash and steering column, then out of the car through the windshield. Today, cars are designed to reduce force through energy absorption while separating passengers from objects that can injure them. In crash tests, a vehicle’s front end should collapse while the cab stays straight enough for the door to still operate, and the passengers inside move only a few inches, shielded by the seatbelt and airbag.


Before the Accident

Electronic stability control has been standard since 2012, and for good reason. The Insurance Institute for Highway Safety (IIHS) found that ESC reduces single car accidents by 41% and single car accident fatalities by 56%. These accidents are caused by a loss of control, which ESC can often prevent by maintaining traction.

Collision detection systems can ready the car for a crash by braking, adjusting seatbelt tension, moving the headrests and even closing windows.


Hitting the Bumper

Current bumpers are required to absorb a 2.5 mph impact, which is great for minor bumps in parking lots and gridlock traffic, but it does little to control impact forces in an accident.


Airbag and Seatbelt Pretensioner Activation

An accelerometer or a mechanical switch located just behind the vehicle’s front clip connects an electrical circuit when it experiences an impact equivalent to hitting a brick wall at 10 to 15 mph. On some vehicles, this activates pretensioners that pull the seatbelts tight to keep passengers from moving around.

This electrical connection also activates an igniter that burns a core of sodium azide that reacts with an outer coating of potassium nitrate, much like a solid rocket booster. The reaction creates a massive amount of nitrogen gas which fills the airbag, propelling it at a speed of 200 mph. By the time your body is moving forward, this bag of gas is in place, ready to cushion the impact and slow you down. Holes in the bag let the gas escape after deployment, while the powder left behind it just talc or cornstarch used inside the airbag container to keep the bag fabric pliable.


Engine Shutdown

The fuel system is designed to shut off automatically in an accident, using either an inertia switch inside the pump or by breaking the electrical connection to the pump when the airbag fires.

Even with the engine off, hybrids still have an active electric drive system. The drive battery connection is broken when the crash sensor is activated, but the 12-volt system used to power the rest of the car is left intact so that safety systems can still operate.


Seatbelt Tensioning

All seatbelts have a centrifugal clutch that tightens if the belt when moved suddenly. Normally, it’s possible to move freely around the seat, but a sudden jerk on the belt, such as what occurs during an accident, locks the belt in place. This keeps the passenger from moving around, preventing them from hitting the front of the cabin and keeping them in the optimum position for contact with the airbag.



Crumple zones are designed to compress easily to absorb the force of an impact. The zones are created using low strength metals, bowed shapes and energy absorbing materials like high-density foam. Some cars are designed with a “submarining” engine: in a crash, the engine mounts swing down and back, sliding the engine away from the cab.


Safety Cell

As much energy as possible needs to be absorbed to reduce the effect on the people inside the car, but the cab needs to maintain its shape to keep objects inside from hitting the passengers. The safety cell’s construction is the opposite of the crumple zone, using high strength materials and straight, rigid structures to maintain the cab’s shape.


Restore Your Car’s Safety After a Crash

You might be fine after a front-end collision, but your car will need some work to get back on the road. Merton Auto Body is an I-CAR Gold Class shop, which means our technicians have the latest in auto body repair training so your car will be fixed right the first time. Stop in at our Sussex, WI location and meet with an appraiser or you can also request an online estimate. We strive to get claims approved by your insurance company quickly so you can have your car back on the road in no time.



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