Carl F. Thelin

DOOR-MOUNTED LAP-SHOULDER BELTS

General Motors used the tension-reliever (DETAIL HERE) with this new seatbelt system when they adopted this hypocritical means of quickly and cheaply (?) satisfying the Federal requirement of automatic crash protection. Automatic crash protection was government-speak for air bags, the proven way of providing crash protection for people unwilling to buckle up the seat belts.

This was one of several concepts explored to meet a requirement proposed by the NHTSA Federal Motor Vehicle Safety Standard 208. FMVSS 208 required that protection for the occupants of the front seat be protected in a frontal crash without any action by the user. This was the so-called Passive Protection requirement. The installation of air bags in the steering wheel and the right hand side of the instrument panel met this need.

GM’s representatives to the DOT National Highway Traffic Safety Administration in Washington, DC insisted that the installation of door-mounted “automatic seatbelt” was a satisfactory reason to delay requiring installation of two front air bags as standard equipment. This hypocrisy was revealed when internal documents showed that even their executives did not agree. That is another story.

A seat belt system that would put itself into place across the lap and over the shoulder of each outboard-seated person would meet that requirement. The GM solution was the door-mounted-seat-belt (DMSB). The retractors for the lap and the separate shoulder strap were buried inside either front door. The shoulder strap passed out through a slot in the top of the window sill, near your shoulder, and then the webbing continued up along the rear edge of the window to a pivoted D-ring that was bolted to the upper rear corner of the window frame. The lap belt came from another slot below the door arm rest. Both straps met at a common latch plate. The latch plate was supposed to be inserted into the buckle at the inboard edge of the front seat – and left there permanently. Oh, I should mention that GM arranged the front seat so that no one would be able to sit in the center, near the driver.

So, they said that all one had to do was to open the door and slide under the two straps that connected the inside surfaces of the door to the buckle. Then close the door. Both belts would indeed be in place where they ought to be.

That sounds good enough on paper. It was awful in real life. Almost no one used the system like that. The just unbuckled the belt, as usual, to get out. The latch plate went back to rest just below the arm rest. Why did they do that? First of all, it took a stronger pull to open the door, in the automatic mode, because of the tension of the seat belt retractors. Second, the straps were not well positioned. The NHTSA rules said you should not need to assist the “automatic” belt with your hands. But, without holding the belts away from your clothing, they resisted you sliding underneath them. Women found that the lap belt would pull the skirt way up.

With the earliest versions of the DMSB, it was hard to push open the door, in the automatic mode, against the tension of the seat belt retractors. The seat belt retractors for both the lap and shoulder belt were inside the door. If you opened the door quickly, the crash sensors reacted to that by locking the belt retractors. Because of that, when you left the belts attached to the console buckle, you had to open the door slowly, against the tension. To overcome that drawback, the DMS designers went the Rube Goldberg route. When you operated the door handle – inside or outside, the dome light would come on. They rigged that electric signal to tell the seat belt retractors not to lock up when the door was been opened. That worked. You still had the tension but not the lock up.

This system, briefly shared by Honda, had the lap and shoulder belt retractors located inside the door structure. The straps terminated in a common latch plate. General Motor’s instructions were to leave the latch plate inserted in the seatbelt buckle in the usual place near the shift console. When you opened the door, you tugged against the tension of the two belt retractors. Then you manually lifted the belts up so you could enter by sliding sideways under them. Getting out was the reverse.

Door mounted seat belts in a Honda were responsible for the complete ejection of two boys from a Honda with door-mounted seat belts. Honda experts contradicted me, the boys, and the investigating police officer, by claiming that the overturned car was facing up the incline toward the road – in order to justify their assertion that the boys were ejected through the broken-out rear window, not through the opened door. We experienced “Jury nullification” when I was sure that Honda’s design was shown to be clearly responsible for the ejection of two teenagers in a multiple roll over. The victims were two neighborhood bad boys in the Deep South. The jury simply did not care for those boys who considered punks.