How Are Seat Belts Tested


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It’s not “sexy (Ed. note,
stop calling cars sexy),” it’s not “rad,” it’s not loud, and it doesn’t add more power, but the humble seat belt might be the greatest automotive invention of all time. Because at the end of the day, you can’t hear that turbo spool up, burn some rubber, or feel that perfect shift if you die, and the seat belt is designed to prevent that from happening.

Like wearing a helmet on a motorcycle, or using a mask in a panny, wearing a seat belt in any vehicle is the smartest way to keep you safe. It has been proven time and time again to prevent you from getting shredded as you’re thrown through knives of glass, slamming your soft brain against the front of your hard skull, and folding your legs into the size of the owner’s manual inside the glove compartment.

As with any car part, seat belts go through testing to ensure they perform at the proper optimal level. You’ve seen how crash tests are done, and that’s part of seat belt testing, but there’s more to it than just making sure the crash dummy stays in place. Seat belts are tested in a variety of ways, and The Drive’s hall monitors, I mean editors, would like to tell you all about it. Join the conversation below.

What’s the Purpose of a Seat Belt?

The purpose of a seat belt is to safely control and stop a person’s inertia in the event of a collision. They also are designed to reduce the force your body takes on by spreading the energy to strong bony parts of the body. TL;DR, they save your butts. 

How Does a Seat Belt Work?

How a seat belt works depends slightly on the time when it was built. On older vehicles, the person gets into the car seat, pulls out more belt than is necessary,  secures the belt into the buckle, and the belt is retracted around a person. In the event of a collision, the belt is designed not to extend again, so the occupant is held in place.

Modern seat belts work slightly differently due to the invention of the pre-tensioner. Buckling in with a modern seat belt is the same process, but its functionality in the event of a crash is different. A modern vehicle senses severe deceleration or an impact, and within milliseconds it activates a pre-tensioner, which tightens on the occupant to provide even better security and safety.

A close-up of a seat belt buckle.


A seat belt tongue, attached to the belt, will lock into the buckle.

Does Every State Require Seat Belts?

Every state’s seat belts have different age requirements and other slight variations. Check AAA’s list of seat belt laws to check the laws in your state.

Components of a Seat Belt

In the past, seat belts were literally a piece of fabric across the lap. Today, thanks to numerous advancements in safety technology, they have many more parts. We dissect below.

Fabric Torso and Lap Belt

Typically made of polyester, the fabric belt is the part of the seat belt that literally goes around your torso and lap. 


The tongue is the piece of metal attached to the seat belt that clicks into and locks in the buckle.


The buckle, which is located at the side of the seat, is the device that accepts the tongue of the seat belt and locks it into place. To release the tongue from the buckle, you need to press the buckle button.


The retractor is what pulls the seat belt back into the spool when tension is released.


The spool is what rolls up the seatbelt when tension is released.

Load Limiter

A load limiter is designed to protect the occupant from seat belt-inflicted injury by releasing some tension on the belt and allowing for a slight amount of movement that will reduce the load taken on by the shoulder, chest, and torso.


A pre-tensioner retracts the seat belt the moment the car thinks it is about to endure an incoming collision. By doing so, it locks the occupant in place and prevents them from being thrown forward.

Seat belt testing goes through numerous stages.


A safety testing mechanism. 

How Are Seat Belts Tested By Manufacturers and Suppliers?

Every single new car comes standard with seat belts in 2021, and the world is a safer place for it. To double down on the safety, manufacturers, and their suppliers, put their products through numerous rounds of testing before the vehicles hit the road. These are the areas manufacturers and suppliers test.

Tensile Strength

Will your seat belt survive stabs from a sharp object? It should, as it’s tested for its tensile strength against exactly those types of attacks.

Tilt Lock Test 

With the tilt lock test, manufacturers determine the strength and safety of the adjustable locking bar on adjustable seat belts.

Retractor Test

Manufacturers put the retractor through its paces by using a variety of measures, such as g-force, to make sure the retractor is going to retract every time, no matter the situation.

Webbing Durability

There’s no point in a seat belt if the fabric webbing is going to stretch to the point of breakage. The webbing durability test makes sure the webbing will not degrade in performance or condition during repeated use.

Cycle Durability

A cycle durability test runs the seat belt through its normal wear and tear of regular usage over and over and over and over and over and over and over and over…

A plaid interior of a Mercedes-Benz SL.


Some cars have seat belts built into the seats.

How Are Seat Belts Tested By the IIHS and NHTSA?

Per the IIHS:

“We don’t do any direct testing of seatbelts, though they are certainly important factors in how well a vehicle rates in a crash test. If a belt allows too much forward movement, for example, it would be reflected as part of a vehicle’s score for restraints.

Belts are tested to ensure they meet regulations through several of the Federal Motor Vehicle Safety Standards. FMVSS 208 sets performance requirements for the restraint systems. FMVSS 209 more specifically addresses seat belt assemblies. FMVSS 210 addresses seat belt anchorages.”

More specifically, the IIHS looks at these things in the various crash tests.

  • Front crash test: “How well the seat belts and airbags work together to control the movement of the dummy or dummies.” 
  • Side crash test: “In this case, we’re looking mostly at head protection from the side airbags.”
  • Head restraints and seats test: “Forces measured on the neck of the dummy, the geometry of the seat, and seat parameters, including the “time it takes for the head to contact the restraint and torso acceleration.”

An early Mercedes-Benz restraint system with seat belts.


Different seat belt designs, such as this Mercedes-Benz example, have been tried throughout the years.

Fast Facts About Seat Belt Safety

These facts focus specifically on the U.S. market and come courtesy of the NHTSA.

  • About 91 percent of adult front-seat passengers reportedly wore their seatbelts in 2019.
  • Seat belts reportedly saved 14,995 lives in 2017.
  • Between 1975 and 2017, seat belts reportedly saved about  374,196 lives.
  • Approximately 47 percent of the 37,133 people killed in car crashes in 2017 were not wearing seat belts.

FAQs About Seat Belts

You’ve got questions, The Drive has answers!

Q: How Do You Know When Seat Belts Are Bad?

A: You’ll notice a seat belt is bad because it will physically deteriorate or break. Regarding the belt, that means the fabric material is fraying, cut, or damaged and no longer offers the same level of protection and safety. Other ways the belt could fail are a broken locking mechanism, a broken retractor, a broken spool, and spring, or a busted buckle.

Don’t blow off a bad seat belt either. If you notice your belt might be damaged, repair or replace it as soon as possible.

Q: Can You Be Ejected From a Car Wearing a Seat Belt?

A: Nothing is 100 percent safe, so it’s theoretically possible, but wearing one significantly reduces the chance of that happening.

Q: Do Airbags Replace the Need for Seat Belts?

A: Absolutely not. Airbags and seat belts are designed to work together. Without a seat belt, it’s possible the 

Let’s Talk, Comment Below To Talk With The Drive’s Editors!

We’re here to be expert guides in everything How-To-related. Use us, compliment us, yell at us. Comment below and let’s talk! You can also shout at us on Twitter or Instagram, here are our profiles.

Jonathon Klein: Twitter (@jonathon.klein), Instagram (@jonathon_klein)

Tony Markovich: Twitter (@T_Marko), Instagram (@t_marko)

Chris Teague: Twitter (@TeagueDrives), Instagram (@TeagueDrives)

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