Interpretation ID: nht75-4.31

DATE: 11/21/75

FROM: AUTHOR UNAVAILABLE; G. G. Mannella for James B. Gregory; NHTSA

TO: Ford Motor Company

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your letter of November 11, 1975, requesting confirmation that a 1976 Ford Motor Company "deluxe continuous-loop seat belt system" satisfies the requirements of Section 7.1.1 of Standard No. 208, Occupant Crash Protection.

Section 7.1.1 requires adjustment of the lap belt portion of a front outboard seat belt assembly "by means of an emergency-locking or automatic-locking retractor" and adjustment in most cases of the upper torso portion "by means of an emergency-locking retractor." The language permits some single retractor, continuous loop systems as long as the single retractor does "automatically adjust" the tension of the lap belt portion to prevent excessive slack. Because of the submarining danger of a slack lap belt, the National Highway Traffic Safety Administration (NHTSA) has restricted the acceptability of continuous loop systems under S7.1.1 in two areas.

In the NHTSA's September 25, 1972, letter to Renault to which you refer, the level of friction in the tongue is discussed and our position is stated that it must have a sufficiently low level to qualify the lap belt portion as "automatically adjustable." In your recent demonstration of the tongue frictions in the Ford 1976 "standard" and "deluxe" continuous loop seat belt systems to NHTSA personnel, we saw no evidence of design deficiency in limited use of those systems.

The other restriction concerns the use of manual and automatic tension relieving devices on the upper portion of continuous loop systems. In our letters of March 9, 1973, and March 27, 1975 (to General Motors), June 13, 1975 (to Chrysler Corporation), and September 5, 1975 (to Takata-Kojyo), the NHTSA has limited the use of tension relieving devices to the upper torso portion of seat belt assemblies that have "an individually adjustable lap belt." It is our view that the 1976 Ford deluxe continuous loop system does not have "an individually adjustable lap belt" within the meaning of Standard No. 208. In this system slack which is introduced into the continuous loop by the "window shade" tension relief device on the upper retractor is directly transferred to the lap belt, thus increasing the risk of submarining if a crash should occur. I would like to point out that issues related to tension relief devices are, however, still outstanding in an NHTSA proposal (Docket 74-32, Notice 1).

I am enclosing a report on "Comfort and Convenience Analysis of Advanced Restraint Systems" of August 1975. This study, conducted by the NHTSA Safety Research Laboratory on a number of different safety belt designs concludes that: "Several aspects of the systems caused difficulties or confusion, but the single-loop 'window-shade' feature most frequently produced problems." In light of our mutual desire to improve safety belt usage levels, I should also like to again recommend to your attention the results of the earlier NHTSA sponsored study "Sources and Remedies for Restraint System Discomfort and Inconveniences" by Man Factors, Inc., that I sent to your company in January 1975.

SINCERELY,

Ford Motor Company

November 11, 1975

Dr. James B. Gregory Administrator National Highway Traffic Safety Administration

Re: Request for Interpretation of FMVSS 208 with regard to the Performance Requirements for a 1976 Ford Motor Company Deluxe Continuous-Loop Seat Belt System

Reference 1: September 25, 1972 letter from Richard B. Dyson (NHTSA) to Mr. Francois Louis (Renault, Inc.)

Reference 2: March 27, 1975 letter from Robert L. Carter (NHTSA) to David E. Martin (General Motors)

On October 23, 1975 we met with you and members of your staff to review and discuss the subject deluxe seat belt system which is contained on the driver side of one of the two 1975 Pinto vehicles that we left for your further review. This continuous-loop belt system incorporates many customer convenience and comfort features which we believe would result in increased belt usage. We also believe we have interpreted correctly the performance requirements of Section 7.1.1 of Standard 208 in light of the two subject references. However, Ford would appreciate receiving assurance that the Administration agrees with our interpretation.

It is the interpretation of the Ford Motor Company, based on the referenced documents, that we as a manufacturer have designed the subject seat belt system to provide:

1. Excellent fit of the lap strap with "automatic adjustment" while donning, due to the constant stored position of the free sliding tongue as specified in Reference 1, which states:

"The characteristic to be avoided is the tendency of the buckle to trap an excessive amount of webbing on the lap belt side of the buckle. This tendency is overcome . . . if the buckle slides down of its own weight while the assembly is stored on the B-pillar so that the next occupant must lengthen the lap belt as he fastens the buckle".

2. A belt system having a tension reliever which, during normal usage of the belt system, will not result in "excessive slack" in the lap strap.

In most instances an intentional, overt act on the part of the user is required to transfer any slack from the shoulder strap to the lap strap without cancelling the tension reliever. Such cancelling permits the retractor spring to "automatically adjust" the lap strap. However, in the unlikely event that occupant action would force "excessive slack" into the lap strap without cancellation of the tension reliever, it would be expected that a conscientious user of seat belts would recognize that he has loosened the lap strap and would readjust the belt system by a simple manual cancellation of the tension reliever.

Ford will provide on the visor sleeve and in the owner's manual instructions to customers indicating the possibility of a loose lap strap and what to do to correct it, such as:

Avoid a loose lap strap; if for any reason you have created slack in your lap strap, lean forward to cancel the tension reliever which will permit the shoulder strap retractor spring to snug the lap strap automatically. Your normal motions while driving will then again activate the tension reliever.

Hence, our belt system with the tension reliever, if used as instructed ("during normal usage"), will, as specified in Reference 2, "automatically adjust the tension of the lap belt portion to prevent excessive belt slack".

Ford also emphasizes that the free-sliding tongue overcomes many customer inconvenience items found in other systems by providing:

* convenient and consistently positioned parking of the tongue for easy access,

* freedom of movement without lock-up to extend webbing during donning due to the free sliding action,

* improved stowage of webbing since the retractor spring does not have to lift the tongue,

* no interference with seat adjustment.

An early response to this letter is urgently requested since this improved belt system is planned for production as a running change during the 1976 model year.

R. E. KIMBALL FOR

J. C. Eckhold Director Automotive Safety Office