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THIS WEEK, A reader asks:
My car is fitted with a seatbelt pretension system and load limiters. What exactly do they do and are they more effective than seatbelts without these?
Belting up is the single most effective thing you can do to protect yourself in a crash. Fact. According to the Royal Society for the Prevention of Accidents (Rospa) Volvo’s three-point seatbelt design, created in 1959, has saved over one million lives worldwide.
A pretensioner, around since the 1950s, is a device designed to make seatbelts even more effective by removing the slack from a seatbelt as soon as an accident is detected or if the system senses excessive seatbelt tension on the driver or passenger’s seatbelt.
On standard seatbelts the locking system stops the seatbelt from extending any farther, but a pretensioner actively pulls in on the belt. This ‘pre’ tensioning of the belt pulls the wearer back firmly into their seat and into a better position to get the full protection of the front airbags. By reducing the movement of the body, it also reduces the risk of injury.
Load limiters are often installed to minimise seatbelt-inflicted injury by releasing a little more excess belt webbing.
You know that extra fold of fabric on your seatbelt? That is a load limiter – and the stitching on that fold is designed to rip and release the extra fabric when excess force is applied. More advanced load limiters use a torsion bar in the retractor mechanism.
But are they any safer than conventional seat belts?
Well, according to one US study, by the National Highway Traffic Safety Administration, they are better:
In passenger cars, CUVs, and minivans, 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 follow up study showed that
a combination of pretensioners and load limiters significantly reduces HIC, chest acceleration, and chest deflection scores on 35 mph frontal NCAP tests.
Want to know more about how a pretensioner and force limiter works? This video will explain more.
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