How Exactly Are Seat Belts Tested for Humans?

These small pieces of fabric have saved countless lives. Here's how they're made and tested.

Once upon a time, we all roamed the back seats of our parent’s cars, footloose and fancy-free! We’d play on the seats, in the footwells, and stare at people out of the back windows! Today, we know that was highly dangerous due to the lack of seat belts.

Seat belts aren’t new inventions, but their widespread use and enforced use are more recent developments. These small pieces of fabric have saved countless lives throughout the years, yet their construction, and how manufacturers test them, are relatively unknown by the general populace.

To satiate that itch for knowledge, Car Bibles’ editors went through the history and government agency’s testing regimen PDFs to find you the education you desire.

A lap belt.
A lap belt. Depositphotos

What Is a Seat Belt?

A seat belt is a mechanical device designed to keep you in place and safe in the result of an automobile accident. They’re meant to keep you from ejecting through the car’s windshield and/or from impacting the steering wheel, dash, and seats in front of you.

The Anatomy of a Seat Belt

There are five pieces of a traditional seat belt.

Fabric Belt

The belt is made of a webbed fabric designed to hold the occupant in place in the case of an accident.

Retractor

A retractor keeps the seat belt wound up in place while not being used by an occupant.

Spool and Spring

The spool and spring are housed in the retractor. These enable the seat belt fabric to be pulled in and out freely when locking and unlocking.

Locking Mechanism

The locking mechanism has two parts, a tongue, and buckle, the former of which goes into the latter. They lock the seat belt in place at your side.

Pre-Tensioner

A pre-tensioner is a modern advancement of seat belts. It includes a gas-propelled mechanism that, when force is detected, will spool up any loose fabric and prime the belt to hold you in place in the event of a crash.

Clicking in a seatbelt.
Clicking in a seat belt.

How Does a Seat Belt Work?

Older seat belts are designed to minimize the force load across your pelvis and chest with the spool and spring having already retracted enough fabric to keep you in place.

Modern seat belts with pre-tensioners use the gas-propelled mechanism to cinch you in place in the event of an accident while minimizing the load across your pelvis and chest. These are usually paired with g-force sensors that automatically kick in when force is detected outside the normal range of braking, throttle, and cornering.

What’s the Difference Between a Seat Belt and a 5-Point Harness?

As described above, a seat belt consists of a retractor, a 3-point strap that goes across your lap and chest, and a locking mechanism at your side. It retracts when force is applied and keeps you secure and more comfortable.

A 5-pt harness is a stationary set of straps that go across both shoulders, both sides of your lap, and one up through the seat across your crotch. These are adjusted manually and don’t feature a pre-tensioner. These are used in child and baby car seats and race seats, as they’re safer than the 3-pt units, though only when paired with enhanced support and head restraints.

How Are Seat Belts Tested?

Throughout the years, seat belts have gone from optional equipment to standard on every car, truck, and SUV. And during that time, federal governments around the world have gotten into the business of including them in safety tests. Today, NHTSA conducts crash testing with dummies to gauge whether or not a vehicle’s safety systems, including its belts, are up to par with the standards set out.

However, there are a few other tests that manufacturers do before NHTSA or EuroNCAP, the European counterpart to NHTSA, get their hands on the vehicles. Here’s how they’re tested.

Tensile Strength

Manufacturers will test the seat belt’s webbing for tensile strength through multiple sharp and sustained loads.

Tilt Lock Test 

A tilt-lock test is designed to see if the adjusting locking bar that keeps the webbing in place can withstand load and repeated use.

Retractor Test

This tests the retractor’s ability to work under a certain set of parameters, including high and low g-force.

Cycle Durability 

Manufacturers will put their seat belt systems through cycle durability tests which repeatedly test the entire system, just as you would use them during normal use.

Webbing Durability

Webbing durability is one of the most important tests and the one that Takata got in trouble for when it was found fudging the numbers. This test examines the durability of the seat belt webbing. You know, the stuff meant to keep you safe!

The Car Bibles Glossary of Seat Belt Terms

Welcome to Bible School!

Lap Belt

An old-school style of the seat belt that, thankfully, isn’t a thing anymore.

Child’s Car Seat

A type of car seat that either uses the existing seat belt or LATCH points to safely secure a child who can’t use the adult seat belts.

Bolstering

Bolstering is a padding that’s been specifically designed within the seat that goes around your midsection, your thighs, and sometimes your head, to keep you further in place in the case of an accident.

The Questionnaire

Car Bibles answers all your burning questions!

Q: Which Automaker Offered the First Seat Belt?

A: Nash offered the first optional seat belt in 1949, but Saab was the first automaker to offer it as standard across its lineup.

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

A: We’re not going to be definitive in our answer due to Murphy’s Law, but you have a notably lesser chance of being ejected with a seat belt on.

Q: How Many People Are Saved By Seat Belts Each Year?

A: According to NHTSA, about 14,995 people are saved thanks to wearing a seat belt each year.

Video on Seat Belt Testing

Car Bibles’ editors understand that not everyone is a text-based learner. For those kinesthetic people out there, we have your back with a video showing you exactly how seat belts are tested. We pulled it from one of our favorites, and most trusted, sources and it’s a great additional resource.

Car Bible’s Favorite Car Products

There aren’t exactly tools or products we’d swear by that relate to seat belts. And most products that are associated with them make them less reliable. So here’s a smattering of our favorite car products that you can use in your car that won’t impact your safety, such as Glass Cleaner, Phone Mounts, and Dog Seat Belts, which actually do work!

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Jonathon Klein

Jonathon KleinJonathon has jumped Aston Martins for Automobile Magazine, clocked 200 mph in a McLaren 720S for Playboy, and sampled his best life behind the wheel of a Ferrari Dino Evo for Road & Track. He’s hopelessly addicted to the strongest coffee he can brew. Please send him more. Contact the author here.