Interpretation ID: 99aiam3.ogm

Mr. George L. Parker
Association of International Automobile Manufacturers
1001 19th St. North
Suite 1200
Arlington, VA 22209

Dear Mr. Parker:

The Associate Administrator for Safety Performance Standards, L. Robert Shelton, has asked me to respond to several concerns that the Association of International Automobile Manufacturers (AIAM) has raised in both correspondence and in a meeting with the agency on August 19, 1998, regarding the interpretation of Standard 201, Occupant Protection in Interior Impact, and the compliance test procedures for that section. Your letter asks that the agency:

• again consider limiting multiple impacts in cases in which target areas are near each other,
• clarify the definition of "convertible roof frame" in the context of Standard 201,
• provide guidance on the position of sun roofs for targeting purposes,
• clarify the procedure for relocating target areas when those targets must be moved, and
• address what AIAM considers to be unacceptable potential variability between target area locations as derived by manufacturers for certification testing and by the National Highway Traffic Safety Administration (NHTSA) for compliance testing.

In the August 19, 1998, meeting, AIAM and other industry participants presented additional information relating to multiple impacts. They also raised issues concerning lower face and cheek contact during testing, and procedures for relocating targets in the event that movable seat backs make a target area inaccessible for testing.

Multiple Impacts

Your letter indicates that AIAM shares the concern raised by the (former) American Automobile Manufacturers Association (AAMA) regarding multiple impacts and that you wish to raise an additional point on this issue. As your letter indicates, AAMA filed a petition for reconsideration in response to the April 8, 1997, final rule modifying the head impact provisions of Standard 201. The AAMA petition, filed on May 23, 1997, requested in part that the agency consider limiting impacts for certain target areas to one impact per individual piece of trim. In its petition, AAMA contended that test impacts may result in damage to trim components that may extend beyond the area in the immediate vicinity of the impact point. AAMA also stated that impacts by the lower face and other portions of the Free Motion Headform (FMH) that are outside of the forehead impact zone may also damage trim so that the ability of the vehicle to withstand an impact at an adjacent target area is compromised. Your letter refers specifically to the potential for an impact by the lower face to cause collateral damage to a second target area when the first is being tested. You state that the lower face and the forehead impact zone of the FMH are approximately 200 millimeters apart and that the existing limitation in S8.14(c) excluding impacts into target areas that are separated by 150 mm or less does not preclude a second impact into a target area that has been damaged by lower face contact resulting from an impact to a nearby target area. Due to this phenomenon, you argue that impacts should be limited to one impact per component.

As you are undoubtedly aware, NHTSA published a denial of the AAMA petition on April 22, 1998. (63 FR 19839) In denying the AAMA petition, the agency noted that AAMA had not submitted any data supporting its position and that the agency continued to believe that the 150 mm minimum distance between target areas was sufficient to prevent overlapping impacts. Accordingly, NHTSA denied the AAMA request to limit impacts to one impact per component.

AAMA presented additional data relating to the consequences of contact between lower portions of the Free Motion Headform and interior trim components during the August 19, 1998, meeting. These data indicate that contact between the lower portion of the FMH and interior trim during testing of one target area may degrade the performance of the trim in the area of the contact to an extent that it may be difficult, if not impossible, for the vehicle to meet the specifications of Standard 201 when tested at a target area in the vicinity of the lower face contact.

The agency recognizes that Standard 201 does not require that a component sustain multiple impacts at a single target area without any degradation in performance. S8.14(c) currently provides that no impact may occur within 150 mm of another impact. This distance was selected because of the possibility that collateral damage could occur when the forehead impact zone of the FMH, which is 125 mm wide, makes contact with an intended target point. In setting this distance, NHTSA did not consider the length of the FMH as well as its width. The agency will initiate rulemaking to consider the possibility of amending the Standard to provide that on certain vertical interior surfaces, notably pillars, roll bars and stiffeners, a target area that is within 200 millimeters of another target area, measured from the center of each target, that has been impacted by the FMH during a compliance test shall be not be tested. The proposal would be limited to vertical surfaces since lower face impacts are most likely to occur on vertical surfaces where the distance between the lower face and the forehead impact zone becomes an issue. However, in cases in which a target on one side of the vehicle is not used because of its proximity to another impact area, the corresponding target on the other side of the vehicle will be used. By testing in this fashion, the agency will be able to test all target points to the requirements of Standard 201 without requiring that targets meet these requirements in multiple impacts.

Lower Face Contact and HIC Calculation

Another item of concern discussed at the August 19, 1998, meeting was the effect of lower face or cheek contact on the measurement of compliance with the Head Injury Criterion (HIC) specified for Standard 201. AIAM, AAMA and others are concerned that, in a number of test configurations, the lower portion of the FMH "face" contacts the vehicle interior either at the same time or very shortly after the forehead impact zone of the FMH contacts a target area. They allege that the contact between the lower portion of the FMH "face" and the vehicle interior in these circumstances results in additional acceleration that may cause the resultant HIC to be higher than it would be if the contact were between the forehead impact zone and the intended target area alone. AAMA recommended that in cases in which the injury reference values are exceeded during compliance testing and it is subsequently determined that early lower face involvement is the cause, the test be rerun with an increased off-set angle sufficient to create an identifiable degree of separation time between forehead impact and the lower face contact. Data developed by General Motors and presented at the August 19, 1998, meeting were used to support the contention that an off-set angle of 25 degrees is needed to delay lower face impact beyond the HIC calculation time period. During that same meeting, Mitsubishi presented an example of a series of tests in which impacts to an upper roof target area resulted in contact between the lower face of the FMH and a nearby B-pillar target, BP-1. According to Mitsubishi, the lower face contact occurred within 6 milliseconds of the forehead striking its intended target, and the accelerations resulting from both impacts could not be distinguished. The result of these two cumulative impacts was purportedly to increase the HIC score to fifty percent above that measured when no lower face contact occurred.

NHTSA does not intend to initiate rulemaking to increase the offset angles beyond those currently contained in Standard 201. In the August 18, 1995, final rule establishing new specifications for Standard 201 (60 FR 43031), the agency indicated that the final rule allowed a five degree lower face offset for targets on the A-pillar and other targets that are not pillars and a ten degree offset for any other pillar. The offset angle provisions were inserted into Standard 201 after several manufacturers submitted comments indicating that early lower face contact could change measured acceleration levels when compared to impacts on an identical target in which lower face contact did not take place. Tilting the FMH in this fashion would create an offset clearance that would delay lower face contact beyond the time of the HIC calculation, which NHTSA found occurred within 20 milliseconds. The five and ten degree offset angles also did not fundamentally alter the kinematics of the FMH other than to delay lower face contact, so that the safety consequences of allowing the use of these angles were not significant. As inserting the five and ten degree offset angles did not have real safety consequences, the agency felt it was appropriate to do so.

Although the data presented at the August 19, 1998, meeting indicate that the existing five and ten degree offsets may not be sufficient to prevent lower face contact during the time of HIC calculation, the agency has reconsidered its earlier position implying that accelerations from lower face contact occuring within 20 milliseconds of forehead impact should not be included in the HIC score. NHTSA has reviewed the research data used during development of Standard 201 to construct the transform function used in calculating HIC when the FMH strikes a vehicle interior. These data include the results from testing in which the FMH was launched into padded and unpadded surfaces mounted at different angles to represent the interior of a vehicle. In some of these impacts, portions of the lower face of the FMH struck portions of the target structure during the period in which the HIC calculation was taking place. As these data were used to develop the method of determining HIC scores in Standard 201, consideration of the effects of impacts of the lower front surface of the FMH on interior surfaces has already been integrated into the transform function. Because the transform function provides the means for determining HIC when the FMH strikes an interior surface, any implication that lower face contact should not be allowed during the time of the HIC calculation because that contact would improperly influence HIC, is contrary to the research data used in developing the Standard. Accordingly, lower face impacts should be included in Standard 201's evaluation of vehicle performance in those instances in which lower face contact results in a higher HIC score.

In real-world crashes, contact between the vehicle interior and portions of the head other than the forehead is common. The agency believes that the interests of safety demand that countermeasures be developed so that impact accelerations do not produce a HIC greater than 1000 in those instances in which the impact occurs over a larger area of the head. While the offset angles now contained in Standard 201 do not significantly reduce impact speed or the kinetic energy resulting from impact, further increases in the lower face offset could have significant safety consequences. Adopting a 25 degree offset, as suggested by AAMA, would reduce the effective impact speed of the FMH by 10 percent and the kinetic energy of the impact by 18 percent. In addition, allowing the FMH to rotate freely during HIC calculations would also dissipate a small portion of the total kinetic energy. Adopting AAMA's recommendation would be equivalent to a 20 percent reduction in the intended allowable impact energy.

While our review of the underlying data indicates that the use of any offset angles is unnecessary, NHTSA does not presently plan to initiate rulemaking to eliminate the existing offsets, as retaining them does not have any negative impact on safety. Increasing the present offset angles beyond that which is currently specified in Standard 201 could, however, have significant safety consequences. The agency is therefore retaining the existing offset angles and is rejecting the suggestion that they be increased.

Impacts with Glazing

Chrysler engineers presented a front header impact test at the August 19, 1998 meeting in which the FMH struck a front header target and then glanced off the target and contacted the windshield. The particular configuration of the front header and the windshield resulted in the FMH striking the target area at a relatively shallow angle, making a glancing impact with the target area, and then contacting the windshield. The resultant HIC was over 1000, while subsequent impacts to the front header which did not involve the FMH striking the windshield produced a HIC of less than 1000.

Standard 201 is not intended to prevent injuries resulting from impacts with glazing. The current test procedure provides that during testing, window glass is to be placed in the down position. In the case of stationary glazing, such as windshields, rear windows, fixed quarter windows or glazing other than sun roofs, it may not be possible to move the glass to prevent impacts with the FMH when an adjacent target area is tested. If the glazing cannot be moved and the anterior portion of the FMH strikes the glass near or at the same time that the forehead impact zone strikes the target, and thereby affects the HIC, NHTSA will regard the test as invalid.

Definition of Convertible Roof Frame

Your letter also asks that NHTSA clarify the definition of "convertible roof frame" as used in S6.3(a) of Standard 201. That section defines "convertible roof frame" as the "frame of a convertible roof." Section 6.3(a) excludes convertible roof frames and roof linkage assemblies from meeting the impact requirements of S6.1 through S6.2. You wish to know if the definition of "convertible roof frame" includes cross members and braces as these components can be considered to be part of the roof frame and suggest that "cross members and roof braces should be excluded because they are difficult to target and test. . ." because they would tend to vibrate or deflect with impact. Finally, you indicate that these structures "are not likely to offer significant head impact risk."

Under common usage, a frame is considered to be a rigid structure formed of relatively slender pieces joined together to provide major support to a building or structure. Under the commonly accepted meaning of "frame," the cross members and braces of a convertible roof would be considered to be part of the "frame" as they are integrated into the larger structure that provides shape and support for the roof itself. Accordingly, as convertible roof frame is presently defined in Standard 201, such braces and cross members are, by definition, excluded from testing.

AIAM is also concerned about hard top convertible roofs. The agency addressed the issue of hard top convertible roofs in its April 22, 1998, denial of the petition filed by ASC, Incorporated.

As indicated in that notice, NHTSA believes that integrated or hard top convertible tops can and must meet the requirements of Standard 201.

Window and Sunroof Position for Targeting and Impact Testing

As observed in your letter, S8.2(c) of Standard 201 indicates that movable sun roofs are placed in the fully open position for compliance testing. However, the Standard does not address the position of movable sun roofs for targeting. AIAM asks if movable sun roofs are placed in the open or closed position for targeting purposes and suggests that NHTSA intended that movable sun roofs be placed in the closed position when targets are located. This conclusion is based on AIAM's view that certain targets, such as the front header target (FH2) could be located at the sunroof opening. AIAM believes that if this target is located on a sunroof opening with the sunroof open, manufacturers would have to test using test configurations in which the head form would travel through an area above the roof line prior to impact. In AIAM's view, such a test configuration "would not be realistic in the real-world" and goes beyond the intent of the Standard to provide protection against the "interior" head impact.

NHTSA believes that those targets that may be located at a sunroof opening should be located with the vehicle in the same condition as during testing. The sunroof should therefore be in the open position. The agency does not share AIAM's view that this procedure is contrary to the intent of the Standard or would produce an absurd result. Pursuant to S8.13, the headform may be launched against a target from any point inside the vehicle, limited only by the approach angle limits specified for that target. While the use of certain vertical approach angles may result in a portion of the head form traveling along a path above the roof line of the vehicle as it travels from a point inside the vehicle, the agency believes that the likelihood of this occurring is small. NHTSA also observes that as the headform originates inside the vehicle, such an impact could occur in real world impacts.

Measured Along the Vehicle Interior Requirement

As set forth in the August 18, 1995 final rule, S8(b) contained the procedure for relocating targets when it was not possible for the forehead impact zone of the FMH to contact a target. That procedure specified that the target could be relocated to any point within a 25 mm circle, measured along the vehicle interior, from the center of the original target. Your letter states that the April 8, 1997, final rule, which amended the procedures in S8(b) (and redesignated the section as S10(b)) for relocating target areas, modified the relocation procedure to allow movement within a sphere rather than a circle. You observe that the procedure continues to provide that the radius of sphere is determined by measuring from the center of the original target area along the vehicle interior and contend that this directive is inconsistent with the April 8, 1997, amendment, as that amendment changed the acceptable relocation area from a circle to a sphere. In your view, measuring the radius of this sphere along the interior would defeat the purpose of specifying a sphere rather than a circle.

We agree with your view. The existing language's specification that the distance be measured along the vehicle interior, which restricts the measurement to following the contour of an interior surface, is not consistent with the use of a sphere for relocating targets. Accordingly, the agency has deleted the reference to "measured along the vehicle interior" found in S10(b) through a technical amendment.

Variability in the Location of Head Impact Target Areas

Your letter also voices AIAM's concern that neither Standard 201 or the compliance test procedure addresses the potential for variation in the location of target areas as determined by manufacturers and the agency when compliance testing is performed. AIAM indicates that the potential for variation between both vehicles and target locations when performed by different parties jeopardizes the ability of manufacturers to certify their vehicle with a high degree of confidence. To address this difficulty, AIAM suggests that NHTSA specify an allowable variation within the 12.7 mm diameter size of the target marker and adopt a set of procedures for the agency to follow in locating target areas. In this suggested procedure, the agency would locate target areas through obtaining drawings of the target areas for a vehicle from the manufacturer and then reach a mutual agreement with the manufacturer regarding the "correct" target locations prior to any agency testing. Once this procedure is concluded, you also urge the agency to further reduce the potential for variations by using the manufacturer's drawings to locate the seating anchorage points to serve as a reference for locating targets with the use of a coordinate measuring machine. AIAM also suggests that a coordinate measuring machine be used to locate CGF1, CGF2, and CGR, reference points that are located in mid-air, to limit inaccuracies that may result from inaccuracies from other measurement and location methods.

The agency acknowledges that the potential for variation between the location of target areas as determined by the manufacturer and the agency exists. NHTSA is also aware that a certain degree of variation may occur between different vehicles manufactured to the same design. Nonetheless, the agency declines to adopt the procedures suggested in your letter. It is the intent of Standard 201 to ensure that proper protection is provided by the various components addressed by the standard and not merely a few target points. In adopting target points rather than zones, the agency rejected the argument that even zones would create unduly burdensome test conditions. (60 FR 43037). Moreover, the existing procedures for locating target areas were carefully developed by the agency and further refined since their inception to address manufacturer arguments that use of larger target areas would require an extensive amount of testing to verify compliance. While some degree of variation between different examples of the same vehicle or between target locations fixed by different entities performing tests is inevitable, NHTSA believes that such variations are not likely to be unpredictable or large. If the agency were to use manufacturer supplied drawings to locate target areas for compliance testing, it would be providing manufacturers with an undue degree of control over the compliance testing process and acting in derogation of the overall purpose of the Standard. It is the manufacturer's responsibility to assure compliance within the range associated with the target points.

The agency observes that the Standard 201 laboratory test procedure contains certain tolerances which, to a degree, address the issue of variability. However, your member companies should be advised that test procedures are not rules, regulations or agency interpretations regarding the meaning of a safety standard and are not intended to limit the requirements of any applicable standard.

Movable Seat Backs

During the August 19, 1998, meeting, concerns were also raised about the possibility of movable seat backs preventing access to target areas and preventing contact between the forehead impact zone of the FMH and the intended target. It is the agency's position that in the case of potential interference between a movable seat back and a target area, the movable seat back should be placed in any adjustment position that may be attained while the vehicle is in motion.

Accordingly, if a seat back may be reclined for comfort or is hinged to allow ingress or egress to an area of the vehicle, targeting and testing of target areas near that seat back will be conducted with the seat back in any position within the range of adjustment or movement.

I hope that this is responsive to your inquiry. If you have any questions, please contact Otto Matheke of this office at (202) 366-5253.

Sincerely,
Frank Seales, Jr.
Chief Counsel
ref:201
d.2/19/99