Interpretation ID: nht75-6.15

DATE: 10/29/75

FROM: AUTHOR UNAVAILABLE; John G. Haviland; NHTSA

TO: Laird E. Johnston -- General Motors Corp.

TITLE: FMVSS INTERPRETATION

TEXT:

Free Sliding Latch With Tension Relieving Feature

Laird E. Johnston ASE - Engineering Staff

The following comments are in reference to your question concerning whether existing safety standards allow a shoulder belt tension relieving feature on a single loop three point belt system having a free sliding (non-cinching) latch.

GM Legal Staff has been consulted concerning interpretation of the present wording in MVSS 203, Section S7.1.1 (Attachment 1) and proposed amendment Docket 74-32 Notice 1 (Attachment 2). Legal Staff and ASE agree that:

a) The current MVSS 203 does not clearly prohibit the use of a free-sliding latch plate with a shoulder belt tension relieving device but the NHTSA interprets MVSS 208 as prohibiting such a system (see Attachment 3), and

b) A proposed amendment to MVSS 208 Docket 74-32 Notice 1, does clearly limit the use of comfort devices to the upper portion of the seat belt assembly - the lap belt portion must remain individually adjustable (i.e. introducing slack into the shoulder belt should not affect the lap portion of the assembly).

In our response to Docket 74-32 Notice 1 (Attachment 4), General Motors agreed that devices to relieve tension should not be used on systems permitting inadvertent misadjustment.

ASE also has reservations about the impact performance of such a system both for adult occupants and when used in conjunction with child seats. Although limited sled tests of one such system resulted in no submarining with up to three inches of slack in the lap belt, there is no assurance that occupants would wear these systems correctly or that all similar belt configurations would perform in this manner. Additionally, GM only recommends the use of the child seat in 1968-1975 domestic made vehicles. All of these vehicles have a lap belt that permits lap belt tension independent of the shoulder belt. Present thoughts are that a separate lap belt tension holding clip will have to be supplied with the child seat if GM were to recommend its usage with a free-sliding latch single loop system.

One compromise you may wish to consider is the use of a friction device on the free sliding latch that would allow free belt transfer from the lap belt to the shoulder but hold minimal lap belt tension, possibly five to ten pounds. This should satisfy the NHTSA but would still pose some problem with improper child seat usage. Another solution, which you are aware of, is providing low shoulder belt tension thus reducing the need for a tension relieving device. A one-way cinching latch is the ideal solution to the performance and compliance questions.

If we can be of any further assistance, please let us know.

(original signed by) John G. Haviland Collision Protection/Restraints Automotive Safety Engineering JGH/rk

Attachments (4)

cc: G. F. Ball E. E. Conner T. G. Wingblad