Seat Belts: Buckle Up the Most Effective Safety Device Inside Your Car

AutoMD.com experts weigh in on the anatomy and purpose of seat belts

Carson, CA – June 24, 2015 – Last month marked ‘National Seat Belt Enforcement Mobilization’ and, even though seat belt use has been on the rise, concerns remain about lack of use, especially among younger drivers at night. To help get the word out, the experts at AutoMD.com are offering insight into the anatomy of seatbelts, how they work and why they’re so effective.


According to the National Highway Traffic and Safety Administration (NHTSA), the seat belt and latch save around 13,000 lives in the United States each year(1) – with thousands more saved had victims buckled up.


“Three-point seat belts save lives. Period,” said Tracey Virtue, Vice President of AutoMD.com. “The technology works, the results are clear, yet there are still drivers on the road that put their lives at risk. By simply clicking into the seatbelt, you might save your life and you definitely will set a good example for all passengers – especially the young ones.”

As obvious as that seems, police departments continue to run “click it or ticket” campaigns to get the word out about how seatbelts are the most effective way to reduce fatalities resulting from a vehicle crash. Consider, for example, that seat belts have saved around 300,000 lives since 1975 and have significantly reduced the risk of moderate to critical injury.(2)


So what makes seat belts such a super safety device? While it may seem a simple belt and latch, the fact is that the safety belt is a complex piece of automotive engineering. As part of their support for National Seat Belt Enforcement Mobilization, the experts at AutoMD.com have taken a closer look at seat belts, how they work and what makes them the most significant lifesaving equipment inside your car. With vehicle safety recalls seemingly the order of the day – 34 million airbags recalled at last count(3) – it’s a timely and valuable reminder why seat belts should not be optional, and why it is so important to keep you and your passengers secure while driving. 


Seat Belt Basics

Say you’re traveling down the road at 55 mph, when the unthinkable happens: you hit another car. Over 4,000 pounds is forced to a sudden and shuddering stop while the passengers continue their forward momentum. In an instant, the seat belts go to work; a pre-tensioner pulls the belt slack tight, the load limiter absorbs the pressure on the passenger, all while the webbing and latch of the belt holds tight. That extra second or two of time before impact with the dashboard is often the difference between serious injury or even death – NHTSA reports that seat belt use reduces crash-related injuries by 50 percent or more.(4) It’s that simple, and that complex: seat belts give passengers a few more precious seconds to stop, reducing the velocity and working with airbags to offer maximum protection. As a result, you keep safe from the velocity of the airbag and the hard, cold reality of the windshield. 


The Anatomy of a Seat Belt

  1. Lap and Shoulder Belts and Latch: The webbing of your seat belt is made up of hundreds of strands of polyester fibers, and can hold the weight of a garden variety Chevrolet Suburban. There’s even some give to the belt material for comfort. A typical lap and shoulder belt is designed to align with the strongest areas of the human body: the ribs and the pelvis. Spreading the energy of the impact across the body minimizes the damage during an accident.
    • AutoMD.com Tip: Be sure to check for fraying, wear or cuts, and listen to the sound of the “click” with the buckle and latch housing. Remember, the webbing of the seat belt is your defense against impact at high rates of speed.
  2. Retractors: At the end of the belt webbing is a spring and spool unit called the retractor. Pull the webbing out and it turns counterclockwise; release the webbing and the spring tightens, moving the spool clockwise until the slack has been brought into the spool. Many retractors also have locking mechanisms, either triggered by the motion of the car or the belt.
    • AutoMD.com Tip: Retractors, or retractor pre-tensioners, are perhaps the most frustrating and common seat belt complaint. When it works, the seat belt should flow out and retract smoothly, without locking. A fussy retractorwill lock your seat belt in place constantly, annoying everyone and compromising safety. You can make sure your retractors are operational by keeping the inside of your car clean (no dirtin the mechanism!) and by having your seatbelt inspected. Don’t try to fix a seatbelt retractor on your own.
  3. Pre-tensioners: Seat belts normally use pre-tensioners along with a retracting mechanism to pull passengers into the seat and away from danger just prior to a collision. It actually pulls in on the belt to remove slack and force the passenger into an ideal crash position, to avoid “submarining.” In many cases, the car’s safety system will activate the pre-tensioners before the air bags in order to minimize air bag impact. In order to pull in the belt webbing, most pretensioners use pyrotechnics (like an air bag) to ignite a small chamber of “igniter” material. That begins a process that ends with the retractor housing pulling inbelt webbing and correcting belt position.
    • AutoMD.com Tip: Most pre-tensioners are activated in the same manner as an airbag, and are connected to the car’s safety system. Don’t try to test or repair a pre-tensioner on your own.
  4. Load Limiters: Designed to reduce belt-inflicted injuries, load limiters release a little bit more belt when force has been applied – so there’s a little extra give in the process of slowing down a person’s velocity. Some load limiters are a simple fold of webbing, released when the thread breaks; others use a torsion bar inside the retractor to provide additional slack.
    • AutoMD.com Tip: According to a NHTSA(5), “A belted driver or right front passenger has an estimated 12.8 percent lower fatality risk if the belt is equipped with a pretensioner and a load limiter, than if it is not equipped with either.” That makes this simple component addition to seat belts quite effective at keeping occupants safe and reducing the severity of injury. Be sure to inspect your seat belt webbing and retractor performance on a regular basis to make sure it performs as intended.