Car Accident Crashworthiness: Seat Belt Types – Restrain the Occupant

Seat belt cases are the most frequent crashworthiness cases you will see because of mandatory use laws. Besides, as a society, we are told by talking anthropomorphic dummies to “Buckle up, don’t be a dummy.” Unfortunately, seatbelts do not work properly 100% of the time.

There are six types of seat belt systems that are found on vehicles even though some are no longer used.

The first type of seat belt system is the 2-point shoulder belt with no lap belt. This design was used by Hyundai, VW(Volkswagen) and the Mitsubishi Precis.

The second system is a 2-point passive (automatic) shoulder belt with manual lap belt. Some vehicles had door mounted shoulder belts like Nissan and KIA. Others had a motorized shoulder belt that was track mounted like Toyota, Ford and Mazda.

The third type is a 3-point door mounted belt where the lap and shoulder belt were attached to the door. This design was used by GM and some Honda designs.

The fourth system is the 3-point B-pillar mounted design. It is the most widely used seat belt system in the world. In fact, this design has been used since the 1970’s.

The fifth system is the integrated ABTS (All Belts To Seat) design, where the seatbelt is mounted to the seat. This design is used by Mercedes, BMW, Chrysler Sebring, Dodge Ram pickup, Buick Roadmaster, Chevrolet Suburban, and Cadillac.

The last type of seat belt system is the lap belt only. This is typically seen in the center seat position of vehicles that have bench type seats, in the rear center seat position or for jump seats.

Tracy Law FirmAs for design problems associated with each seat belt system, the 2-point passive shoulder belt designs were inherently flawed because in rollovers, there was no passive lap belt to prevent ejection. Also, in the event the door opened, the occupant
could be swept out of the vehicle. Moreover, in frontal and side impacts, the lack of passive lap restraint allowed the occupant to submarine under the shoulder belt. This resulted in decapitation type injuries and cervical/hangman’s fractures. The most common injury pattern with this design was internal organ injuries since the belt was so stiff and the belt geometry (fit) so inadequate that the internal organs were overloaded due to the placement of the belt.

These same two-point belt related injuries in the 1950’s and 1960’s resulted in the two-point being banned worldwide. In the US, a loophole in the FMVSS permitted their re-introduction.

The 3-point door mounted belt design was flawed in a number of ways as well. Specifically, GM vehicles whose doors would open because they contained a Type III door latch rendered the door mounted belt useless. The door mounted belt also caused a phenomena known as occupant rebound where the restrained occupant would sling- shot rearward with a significant velocity. As a result, restrained dummies impacted the mounting bracket with their head. Another frequent problem with this system involved the loss of restraint effectiveness if the door side rail collapsed since the seat belt was attached to the door.

The 3-point B-pillar mounted belt design has had a checkered past but has saved many lives. A frequent complaint with this design is that the retractor locking device does not lock up timely. An entire book could be written on the various types of retractors. The most prevalent problems with retractors include skip locking, unlocking during rollovers, non-actuation of the deadman/pendulum sensing mechanism and retractor housings actually cutting the webbing. Other design problems included the use of slack inducing devices and failure to install secondary locking devices such as web grabbers/web lockers or pensioners to limit loading on the occupant.

The integrated ABTS seat belt that is mounted to the seat is arguably the best seat belt design in the world because the occupant is tied to the seat not the vehicle. This design encompasses engineering technology developed in the aerospace industry and proven safe in the racing industry. The ABTS design requires a stronger seat base and frame which in turn helps keep the occupant upright during an accident. In non-ABTS vehicles, the seatback frequently deforms rearward in relatively minor rear impact accidents. Since the seat belt is attached to the vehicle body (i.e. door, B-pillar), the restraint system in a non-ABTS vehicle is virtually useless once the seat back is deformed.

In ABTS vehicles, even if the seat collapses rearward, the belt is functional since it is mounted to the seat.  In side impact cases, the ABTS design helps keep the occupant’s head from penetrating the breach of the vehicle.  However, the ABTS must be designed properly, or it too is dangerous. Certain ABTS designs have a tendency to have its seat mounted retractors pull completely free from the seat. Also, these same vehicles’ seat tracks are prone to disengage due to the added stress associated with having the occupant tied to the seat.

The lap belt only is an extremely treacherous design because the occupant, typically a child, hyperflexes forward so violently that his spine is severely fractured or his internal organs are ripped and lacerated. It is believed by some  that children are better off without any type of seat belt than if  they  are only restrained by a lap belt.

The Tracy Firm in Dallas TX assert the rights of individuals injured in vehicle accidents due to manufacturing design, safety system failures, vehicle aggressivity and vehicle crashworthiness throughout the United States. If your injuries were the result of a defective automobile or car part, we can help you assess your legal options.

Contact us online, or, call us today at 214-324-9000 if you or your loved ones are seriously injured in an accident, and, find out if you have a Vehicle Crash worthiness Case.

Source:  The TRACY Firm | August 15th 2012 | Updated: July 5th 2014

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