Interpretation ID: nht72-4.4

DATE: 08/25/72

FROM: AUTHOR UNAVAILABLE; Robert L. Carter; NHTSA

TO: Motor Vehicle Manufacturers Association

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your request of August 7, 1972, for the data used to support the conclusions we announced in Notice 20 of Docket 69-7 concerning the ignition interlock for the center front position and the ability of seat belt systems to meet a 60g, 3-millisecond injury criterion in 1975.

In evaluating the petitions for reconsideration of the center seat interlock requirements, we followed the techniques of cost/benefit analysis adopted in our earlier studies of passive restraints (see General Reference items 42, 43, and 99). The anticipated incremental benefit from an interlock at the center position was $ 9.70 per vehicle, which, when divided by the incremental cost of $ 7.00 supplied by Ford Motor Company (N<16>-69-7-3), produced a favorable ratio of 1.4. Although the analysis was completed, it was used as a rough working paper and was not submitted to the docket. A typed draft of the analysis is being prepared for submission to the docket.

Although we decided to grant interim relief for belt systems from the 60g, 3-millisecond chest injury criterion, several manufacturers submitted data which indicated to us that their present systems were capable of meeting the criterion or that they were close enough that minor modifications would enable them to meet it. The data from your own organization (N<13>-69-7-16) showed that a number of cars were passing the criterion by comfortable margins. The Chrysler data, for example, revealed that in 9 tests no dummy recorded chest accelerations in excess of 50g's. Although General Motors, in its comment, submitted data on subcompacts which indicated a problem with chest accelerations, the data from their larger vehicles ranged between 38 and 52g's. (N<13>-69-7-20). Toyota also submitted test results with most accelerations in the range of 45-50g's, with only one test of a Corolla appearing to show a marginal condition (N<13>-69-7-23).

From our research contracts, a number of sled tests have been conducted at Cornell Aeronautical Laboratory (General Reference No. 135), and most of these produced accelerations of between 30 and 50g's. From other sources have come data indicating that such improvements in belt design as the use of tear seams can produce significantly lower accelerations (see, e.g., General Reference items 161, 166, and 167).