Building a Better Seatbelt

May 8, 2019

More than 50 years ago the federal government ordered car makers to install seat belts.  Originally designed for an average American man – 5 feet, 9 inches tall and 170 pounds – they have saved millions of lives. But one-third of adults in this country are now obese, and seatbelts aren’t working so well for them. 

That’s why engineers at the University of Virginia are studying the science of seatbelts, hoping to create safer restraints. 

Project manager Hamed Joodaki at UVA's Center for Applied Biomechanics
Credit UVA

It’s  testing time at the University of Virginia’s Center for Applied Biomechanics. A team of six engineers will simulate a collision at 20 miles an hour to learn more about how lap and shoulder belts protect drivers and passengers.  Jason Kerrigan is the center’s deputy director. He says seatbelts are more complicated than you might think.

“When you put your seatbelt on, you pull the seatbelt out of this retractor.  The retractor is the spring-loaded part that coils the seatbelt up, but in a crash what happens is that retractor actually is going to spin very quickly and yank on the belt.  It’s going to pull it pretty tightly against your body.  How hard it pulls and at what time it pulls are things that we can adjust about the belt,” Kerrgian explains.

What we can’t do, he adds,  is to assure that belts hold people in the right places.

Research engineers Brian Overby and Patrick Foltz run crash tests to help design a better seatbelt.
Credit RadioIQ

“The belt is going to apply forces to your body to slow your body down with the car, and what you want is those forces to be applied to the strongest parts of your body, across your pelvis, across your hips and across your chest – on your sternum and on your collar bone.”

But if someone has significant belly fat, the belt may slide up, and the wearer can slide under – a movement experts call submarining.  Graduate student and project manager Hamed Joodaki says that increases the risk for serious injuries.

“For example the knees might hit the lower instrument panel, and that is why knee injuries are commonly observed among obese occupants involved in frontal crashes when we look at real world crash data. Also, the feet, arms and the hands become more likely to hit the vehicle interior,” he says. 

A team of research engineers at UVA reviews data from a crash to help design a better seatbelt.
Credit RadioIQ

Research engineers Brian Overby and Patrick Foltz add that such accidents can lead to lifelong disability or even death in obese drivers and passengers.

“In a frontal crash they typically go into the wheel well, and it would be a double femur, double fidtib injury -- breaking all three of the big bones in your leg, which is catastrophic and you’d probably bleed out and die from,” says Overby.

“If you ve somebody injured in a vehicle and they lose the use of their legs, and if you can avoid that, that’s a tremendous impact,” Foltz adds.

Some of the tests done here involve a sled – the body of a car traveling along a rail, then stopping suddenly.

Engineers collect detailed data on what happens to passengers in the back seat, the front seat – sitting up or reclining. 

They also experiment with seatbelts – pulling them hard and fast to see how bodies of different shapes respond. Already, Kerrigan says, automotive safety systems make split-second adjustments based on the nature of a crash.

“If it’s a side crash, it fires the side air bag.  If it’s a frontal crash, it fires a front air bag. If you don’t have someone heavy enough in the right front passenger seat, the right front airbag turns off, because they assume it’s a child in the seat, and poor deployment could cause an injury. In the future, a situation might say, ‘I’ve got an obese occupant in the seat who’s obese,  so I’m going to change the way I restrain that occupant.”

And, he says, cars might make other adjustments based on gender.

“We know that women are more likely to die in a crash than a male, and we know that the injury distributions are different.  We originally thought that just by scaling for size differences we could account for those differences in injury risk, but what we’re finding is that scaling isn’t good enough.”

The center is also working with the Children’s Hospital of Philadelphia to make car travel safer for kids.  Kerrigan and Joodaki hope to have findings later this year to guide decisions about how the federal government will regulate the seatbelts of the future.  

***Editor's Note: The University of Virginia is a financial supporter of Radio IQ.