Ms. Susan Ohara
Safety Engineering
Mitsubishi Motors of America
Ann Arbor Laboratory
3735 Varsity Drive
Ann Arbor, MI 48108

Dear Ms. Ohara

This is in response to your letter requesting information regarding the requirements of Standard No. 201, Head Impact Protection. Specifically, your question relates to locating the B-pillar reference point (BPR) where the specific characteristics of the vehicle interior create difficulties in locating that point. Your letter and accompanying drawings indicate that in the vehicle in question, a groove or indentation is formed at the intersection of the side rail trim and the edge of the interior surface of the roof. You note that S10.2(a) directs that BPR is the point "located at the middle of the line from Point 3 to Point 4 in Plane 7, measured along the vehicle interior surface." The presence of the groove presents the choice of locating BPR either through measuring along the actual surface of the side rail and roof or by using a flexible tape to bridge the groove and measure along the "nominal" surface between Point 3 and Point 4. You further note that if the latter course is followed that BPR will be located on a point in space and ask how you should proceed in relocating BPR so that it is located on the surface of the vehicle interior.

If, as is the case with the vehicle represented in the drawings attached to your letter, the radius of curvature of the groove or indentation located between Point 3 and Point 4 is such that the forehead impact zone of the FMH could not contact any point beneath the nominal surface, BPR should be located by measuring along that nominal surface.

NHTSA stated, at page 16723 of the final rule published on April 8, 1997 (62 FR 16718), that measurements along trim with small convolutions, gaps or depressions would be made nominal to the surface. If following that direction and measuring along the nominal surface results in BPR being located at a point in space rather than on the interior surface of the vehicle, target BP1 must be relocated but BPR must remain in its original location.

In cases where the forehead impact zone of the FMH cannot make contact with a target point, S10(b) provides a procedure for relocating targets within a 25 millimeter sphere centered at the original target:

(b) Except as specified in S10(c), if there is no combination of horizontal and vertical angles specified in S8.13.4 at which the forehead impact zone of the free motion headform can contact one of the targets located using the procedures in S10.1 through S10.13, the center of that target is moved to any location within a sphere with a radius of 25 mm, centered on the center of the original target and measured along the vehicle interior, which the forehead impact zone can contact at one or more combination of angles.

If it is still not possible for the forehead impact zone to make contact within the sphere described in S10(b), S10(c) provides that the sphere may be expanded in 25 mm increments until contact can be made.

I hope that this is responsive to your inquiry. Please contact Otto Matheke of my staff at (202) 366-5263 or through electronic mail at omatheke@nhtsa.dot.gov if you have any questions.

Sincerely,
John Womack
Acting Chief Counsel
ref:207
d.5/13/98