Federal Motor Vehicle Safety Standards; Head Restraints, 25484-25524 [07-2011]

Agencies

• National Highway Traffic Safety Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 72, Number 86 (Friday, May 4, 2007)]
[Rules and Regulations]
[Pages 25484-25524]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 07-2011]



[[Page 25483]]

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Part III





Department of Transportation





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National Highway Traffic Safety Administration



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49 CFR Parts 571 and 585



 Federal Motor Vehicle Safety Standards; Head Restraints; Final Rule

Federal Register / Vol. 72, No. 86 / Friday, May 4, 2007 / Rules and 
Regulations

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Parts 571 and 585

[Docket No. NHTSA-2007-27986]
RIN 2127-AJ96


Federal Motor Vehicle Safety Standards; Head Restraints

AGENCY: National Highway Traffic Safety Administration (NHTSA), DOT.

ACTION: Final rule; response to petitions for reconsideration.

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SUMMARY: This document completes the agency's response to petitions for 
reconsideration of the December 2004 final rule upgrading our head 
restraints standard. We are partially granting and partially denying 
the petitions.
    We are making two changes related to the backset requirement. 
First, to address concerns about variability in measurements, we are 
specifying that backset is determined by taking the arithmetic average 
of three measurements, rather than using a single measurement. Second, 
we are slightly relaxing the backset requirement by specifying that the 
55 mm backset limit applies with the seat back at the vehicle 
manufacturer's specified design angle rather than at 25 degrees. This 
decision reflects consideration of interrelated issues and data 
concerning the 55 mm backset limit, consumer comfort, and seat back 
angle.
    In addition, we are making a number of other amendments. We are 
making changes related to non-use positions of rear seat head 
restraints, requirements for gaps between the head restraint and seat 
back, and the backset and height retention (lock) tests, as well as a 
number of changes in other areas. For the front seat requirements, we 
are providing one additional year of leadtime and also establishing a 
one-year phase-in with an 80 percent requirement. The agency previously 
delayed the compliance date for voluntarily installed rear outboard 
head restraints by two years. In this document, we are also 
establishing a one-year 80 percent phase-in for those requirements. 
Finally, we respond to a petition for rulemaking concerning 
requirements included in the upgraded head restraints rule.
    Today's amendments will not affect the costs of the December 2004 
final rule. However, the agency estimates that the change in seat back 
angle to provide greater flexibility with respect to backset will 
result in a 20 percent reduction in the number of whiplash injuries 
prevented by upgraded front seat head restraints, compared to the 
benefits estimated in the December 2004 final rule. Whiplash injuries 
are Abbreviated Injury Scale (AIS) 1 injuries.
    The agency has separately been leading efforts to develop a Global 
Technical Regulation (GTR) on head restraints, under the United Nations 
Economic Commission for Europe 1998 Global Agreement. Some issues 
raised by petitioners for reconsideration, including ones related to 
backset and testing of dynamic systems, are also being discussed in the 
context of the GTR. While it is necessary for us to issue today's 
decision in order to respond to the outstanding petitions for 
reconsideration, we note that if agreement is achieved on the GTR, we 
will consider making changes in these and other areas.

DATES: Effective Date: This rule is effective July 3, 2007.
    Petitions: Petitions for reconsideration must be received by June 
18, 2007.

ADDRESSES: Petitions for reconsideration should refer to the docket 
number and be submitted to: Administrator, Room 5220, National Highway 
Traffic Safety Administration, 400 Seventh Street, SW., Washington, DC 
20590. Please see the Privacy Act heading under Regulatory Notices.

FOR FURTHER INFORMATION CONTACT: For non-legal issues, you may contact 
Louis Molino of the Office of Rulemaking, Office of Crashworthiness 
Standards, Light Duty Vehicle Division, NVS-112, (Phone: 202-366-2264; 
Fax: 202-366-4329; E-mail: Louis.Molino@dot.gov).
    For legal issues, you may contact Edward Glancy of the Office of 
Chief Counsel, NCC-112, (Phone: 202-366-2992; Fax 202-366-3820).
    You may send mail to both of these officials at the National 
Highway Traffic Safety Administration, 400 7th Street, SW., Washington, 
DC 20590.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Background
    A. Current Head Restraints
    B. The Safety Concern--Whiplash Injuries
    C. Understanding Whiplash
    D. Previous Regulatory Approach
    E. Current Knowledge
    F. January 2001 Notice of Proposed Rulemaking
    G. December 2004 Final Rule
II. Petitions for Reconsideration
III. Development of Global Technical Regulation on Head Restraints
IV. March 2006 Partial Response to Petitions
V. Overview of Decision
VI. Response to Petitions
    A. Backset Requirement
    B. Rear Seat Non-Use Positions
    C. Dynamic Option
    D. Clarification of Removability Requirement
    E. Height Requirement
    F Gaps Between Head Restraint and Seat Back
    G. Backset and Height Retention (Lock) Tests
    H. Energy Absorption Test and Seat Back Bracing
    I. Head Restraint Clearance
    J. Width of Head Restraints for Certain Seats
    K. Option To Comply With ECE 17
    L. Temperature and Humidity Specifications
    M. Owner's Manual Requirements
    N. Nature of Standard
    O. Leadtime
    P. Technical Amendments and Typographical Corrections
VII. Kongsberg Petition for Rulemaking
    A. Summary of Petition
    B. Effective Backset
    C. Backset Retention and Displacement
    D. Height Retention
    E. Non-Use Position
    F. Definition of Rear Head Restraint
    G. Gaps
    H. Removability of Head Restraints
VIII. Rulemaking Analyses and Notices

I. Background

    On December 14, 2004, NHTSA published in the Federal Register (69 
FR 74848) a final rule \1\ upgrading NHTSA's head restraint standard in 
order to reduce whiplash injuries in rear collisions. For front seat 
head restraints, the final rule provided that the upgraded standard 
becomes mandatory for all vehicles manufactured on or after September 
1, 2008. For head restraints voluntarily installed in rear outboard 
designated seating positions, the requirements become mandatory on 
September 1, 2010.\2\ In this section, we discuss the highlights of the 
December 2004 rule, and the safety concerns and other considerations 
that led the agency to adopt it.
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    \1\ Docket No. NHTSA-2004-19807.
    \2\ The September 1, 2010 date was established in a final rule; 
partial response to petitions for reconsideration published in the 
Federal Register (46 FR 12145) on March 9, 2006.
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A. Current Head Restraints

    Vehicle manufacturers currently use three types of head restraints 
to meet the requirements of FMVSS No. 202. The first type is the 
``integral head restraint,'' which is non-adjustable and is built into 
the seat. It typically consists of a seat back that extends high enough 
to meet the height requirement of the standard. The second type is the 
``adjustable'' head restraint, which consists of a separate cushion 
that is attached to the seat back, typically by two sliding metal 
shafts. Adjustable head restraints

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typically adjust vertically to accommodate different occupant seating 
heights. Some also provide adjustments to allow the head restraint to 
be moved closer to the occupant's head. The third type is the active 
head restraint system, which deploys in the event of a collision to 
minimize the potential for whiplash. During the normal vehicle 
operation, the active head restraint system is retracted.

B. The Safety Concern--Whiplash Injuries

    Whiplash injuries are a set of common symptoms that occur in motor 
vehicle crashes and involve the soft tissues of the head, neck and 
spine. Symptoms of pain in the head, neck, shoulders, and arms may be 
present along with damage to muscles, ligaments and vertebrae, but in 
many cases lesions are not evident. The onset of symptoms may be 
delayed and may only last a few hours; however, in some cases, effects 
of the injury may last for years or even be permanent. The relatively 
short-term symptoms are associated with muscle and ligament trauma, 
while the long-term ones are associated with nerve damage.
    Based on National Automotive Sampling System (NASS) data, we 
estimate that between 1988 and 1996, 805,581 whiplash injuries \3\ 
occurred annually in crashes involving passenger cars and LTVs (light 
trucks, multipurpose passenger vehicles, and vans). Of these whiplash 
injuries, 272,464 occurred as a result of rear impacts. For rear impact 
crashes, the average cost of whiplash injuries in 2002 dollars is 
$9,994 (which includes $6,843 in economic costs and $3,151 in quality 
of life impacts, but not property damage), resulting in a total annual 
cost of approximately $2.7 billion.
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    \3\ Non-contact Abbreviated Injury Scale (AIS) 1 neck.
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C. Understanding Whiplash

    Although whiplash injuries can occur in any kind of crash, an 
occupant's chances of sustaining this type of injury are greatest in 
rear-end collisions. When a vehicle is struck from behind, typically 
several things occur in quick succession to an occupant of that 
vehicle. First, from the occupant's frame of reference, the back of the 
seat moves forward into his or her torso, straightening the spine and 
forcing the head to rise vertically. Second, as the seat pushes the 
occupant's body forward, the unrestrained head tends to lag behind. 
This causes the neck to change shape, first taking on an S-shape and 
then bending backward. Third, the forces on the neck accelerate the 
head, which catches up with--and, depending on the seat back stiffness 
and if the occupant is using a shoulder belt, passes--the restrained 
torso. This motion of the head and neck, which is like the lash of a 
whip, gives the resulting neck injuries their popular name.

D. Previous Regulatory Approach

    As discussed in the NPRM preceding the December 2004 final rule, a 
historical examination of head restraint standards in this country 
indicates that the focus has been the prevention of neck hyperextension 
(the rearward movement of the head and neck over a large range of 
motion relative to the torso), as opposed to controlling lesser amounts 
of head and neck movement in a crash.
    The predecessor to FMVSS No. 202 was General Services 
Administration (GSA) Standard 515/22, which applied to vehicles 
purchased by the U.S. Government and went into effect on October 1, 
1967. GSA 515/22 required that the top of the head restraint achieve a 
height 700 mm (27.5 inches (in)) above the H-point.\4\ Also in 1967, 
research using staged 48 kilometer per hour (kph) (30 mile per hour, 
mph) crashes concluded that a head restraint 711 mm (28 in) above the 
H-point was adequate to prevent neck hyperextension of a 95th 
percentile male. FVMSS No. 202, which became effective on January 1, 
1969, required that head restraints be at least 700 mm (27.5 in) above 
the seating reference point or limit the relative angle between the 
head and the torso to 45 degrees or less during a dynamic test.
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    \4\ The H-point is defined by a test machine placed in the 
vehicle seat (Society of Automotive Engineers (SAE) J826, July 
1995). From the side, the H-point represents the pivot point between 
the torso and upper leg portions of the test machine. It can be 
thought of, roughly, as the hip joint of a 50th percentile male 
occupant viewed laterally.
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E. Current Knowledge

    There are many hypotheses as to the mechanisms of whiplash 
injuries. Despite a lack of consensus with respect to whiplash injury 
biomechanics, there is research indicating that reduced backset, i.e., 
the horizontal distance between the rear of the occupant's head and the 
head restraint, will result in reduced risk of whiplash injury. For 
example, one study of Volvo vehicles reported that, when vehicle 
occupants involved in rear crashes had their heads against the head 
restraint (an equivalent to 0 mm backset) during impact, no whiplash 
injury occurred.\5\ By contrast, another study showed significant 
increase in injury and duration of symptoms when an occupant's head was 
more than 100 mm away from the head restraint at the time of the rear 
impact.\6\
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    \5\ Jakobsson et al., Analysis of Head and Neck Responses in 
Rear End Impacts--A New Human-Like Model. Volvo Car Corporation 
Safety Report (1994).
    \6\ Olsson et al., An In-depth Study of Neck Injuries in Rear-
end Collisions. International IRCOBI Conference, pp 269-280 (1990).
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    In addition, the persistence of whiplash injuries in the current 
fleet of vehicles indicates that the existing height requirement is not 
sufficient to prevent excessive movement of the head and neck relative 
to the torso for some people. Specifically, the head restraints do not 
effectively limit rearward movement of the head of a person at least as 
tall as the average occupant. Research indicates that taller head 
restraints would better prevent whiplash injuries because at heights of 
750 to 800 mm, the head restraint can more effectively limit the 
movement of the head and neck.
    In a recent report from the Insurance Institute for Highway Safety 
(IIHS), Farmer, Wells, and Lund examined automobile insurance claims to 
determine the rates of neck injuries in rear end crashes for vehicles 
with the improved geometric fit of head restraints (reduced backset and 
increased head restraint height).\7\ Their data indicate that these 
improved head restraints are reducing the risk of whiplash injury. 
Specifically, there was an 18 percent reduction in injury claims. 
Similarly, NHTSA computer generated models have shown that the 
reduction of the backset and an increase in the height of the head 
restraint reduces the level of neck loading and relative head-to-torso 
motion that may be related to the incidence of whiplash injuries.\8\
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    \7\ Farmer, Charles, Wells, JoAnn, Lund, Adrian, ``Effects of 
Head Restraint and Seat Redesign on Neck Injury Risk in Rear-End 
Crashes,'' Insurance Institute For Highway Safety, October 2002.
    \8\ ``Effect of Head Restraint Position on Neck Injury in Rear 
Impact,'' World Congress of Whiplash-Associated Disorders (1999), 
Vancouver, British Columbia.
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    With respect to impact speeds, research and injury rate data 
indicate that whiplash may occur as a result of head and neck movements 
insufficient to cause hyperextension. Staged low speed impacts indicate 
that mild whiplash symptoms can occur without a person's head exceeding 
the normal range of motion. This means that our previous focus on 
preventing neck hyperextension is insufficient to adequately protect 
all rear impact victims from risks of whiplash injuries. Instead, to 
effectively prevent whiplash, the head restraint must control smaller

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amounts of rapid head and neck movement relative to the torso.
    In sum, in light of recent evidence that whiplash may be caused by 
smaller amounts of head and neck movements relative to the torso, and 
that reduced backset and increased height of head restraints help to 
better control these head and neck movements, we concluded that head 
restraints should be higher and positioned closer to the occupant's 
head in order to be more effective in preventing whiplash.
    Further, information about consumer practices regarding the 
positioning of adjustable head restraints indicates that there is a 
need to improve consumer awareness and knowledge of the importance of 
properly adjusted head restraints. Specifically, in 1995, NHTSA 
surveyed 282 vehicles to examine how well head restraints were adjusted 
and if the restraints should have been adjusted higher. Approximately 
50 percent of adjustable head restraints were left in the lowest 
adjustable position. Three quarters of these could have been raised to 
decrease whiplash potential by bringing the head restraint higher in 
relation to the center of gravity of the occupant's head. The 
information was included in a report \9\ for which the agency requested 
public comment. 61 FR 66992; December 19, 1996.
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    \9\ The report was included in Docket No. 96-22, Notice 1. It is 
noted that this NHTSA docket pre-dates the DOT DMS system.
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F. January 2001 Notice of Proposed Rulemaking

    Using the new information gained about the effectiveness of head 
restraints, on January 4, 2001, NHTSA published in the Federal Register 
(66 FR 968) a notice of proposed rulemaking (NPRM) to improve the 
effectiveness of head restraints. The agency proposed new height and 
backset requirements, and other requirements, described below. NHTSA 
also proposed that head restraints be required in the rear outboard 
seating positions.
    In the proposed FMVSS No. 202a, manufacturers were given the option 
of meeting either of two sets of requirements. The first set was a 
comprehensive group of dimension and strength requirements, compliance 
with which is measured statically. The second set was made of 
requirements that would have to be met in a dynamic test.\10\
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    \10\ The previous version of FMVSS No. 202 also features two 
sets of requirements; one applies to statically tested head 
restraints and the other to dynamically tested head restraints.
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1. Proposed Requirements for Head Restraints Tested Statically
    To ensure that head restraints would be properly used in a position 
high enough to limit hyperextension, the NPRM proposed the following 
height requirements. The top of the front integral head restraint would 
have to reach the height of at least 800 mm above the H-point. The top 
of the front adjustable head restraint would have to reach the height 
of at least 800 mm above the H-point, and could not be adjusted below 
750 mm. The top of the rear mandatory head restraint could be adjusted 
below 750 mm above the H-point. The NPRM also proposed that adjustable 
head restraints must lock in their adjustment positions. NHTSA proposed 
to retain existing requirements for head restraint width.\11\ To 
control even smaller amounts of rapid head and neck movement relative 
to the torso than the amount of relative motion resulting in neck 
hyperextension, the NPRM proposed also to limit the amount of backset 
to 50 mm (2 in) for both front and rear outboard head restraints. In 
addition, the NPRM also proposed maximum gap requirements for head 
restraint openings within the perimeter of the restraint, and for 
height adjustable head restraints, between the seat and head restraint.
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    \11\ 254 mm (10 in) for restraints on bench-type seats, and 171 
mm (6.75 in) for restraints on individual seats.
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    The agency also proposed to prohibit head restraints in the front 
seats from being removable solely by hand, i.e., without use of tools. 
Comments were requested on applying such a requirement to rear seat 
head restraints. Rear seat head restraints could be folded or retracted 
to ``non-use'' positions if they give the occupant an ``unambiguous 
physical cue'' that the restraint is not properly positioned by 
altering the normal torso angle of the seat occupant or automatically 
returning to a ``use'' position when the seat is occupied.
    In addition, the NPRM proposed that these statically-tested head 
restraints would have to meet a new energy absorption requirement, 
compliance with which would be measured using a free-motion impactor. 
Additionally, the agency proposed placing a minimum on the radius of 
curvature for the front surface of the vehicle seat and head restraint. 
The NPRM proposed modifications to the existing strength versus 
displacement test procedure to require simultaneous loading of the back 
pan \12\ and the head restraint, and to remove the allowance for seat 
back failure.
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    \12\ The back pan is the portion of the SAE J826 manikin (July 
1995) that comes in contact with the seat back. Its shape is 
intended to simulate the shape of an occupant's back and thus allow 
for a realistic load distribution.
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2. Proposed Requirements for Head Restraints Tested Dynamically
    The NPRM proposed a dynamic test alternative and said that the 
purpose was to ensure that the final rule does not discourage or 
preclude continuing development and implementation of active head 
restraints and other advanced seat back/head restraint systems designed 
to minimize rear impact injuries. Specifically, the NPRM proposed that 
head restraints tested dynamically would have to meet a Head Injury 
Criterion (HIC) limit of 150 with a 15 millisecond (ms) window. In 
addition, NHTSA proposed a head-to-torso rotation limit of 20 degrees 
when testing with a 95th percentile male dummy in front outboard seats, 
and of 12 degrees when testing with a 50th percentile male dummy in all 
outboard seats.\13\ Further, the NPRM proposed that the head restraints 
must have the same lateral width specified for statically tested 
restraints.
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    \13\ Changes to the dynamic test procedures were also proposed, 
including a new sled pulse corridor. Also, the entire vehicle would 
be mounted on the test sled, not merely the seat.
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G. December 2004 Final Rule

    On December 14, 2004, after considering the public comments and 
other available information, NHTSA published in the Federal Register 
(69 FR 74848) a final rule upgrading Federal Motor Vehicle Safety 
Standard No. 202, Head Restraints (FMVSS No. 202). The new upgraded 
version of the standard was designated as FMVSS No. 202a.
1. In General
    To provide better whiplash protection for a wider range of 
occupants, the rule required that front outboard head restraints meet 
more stringent height requirements. Fixed front head restraints must be 
not less than 800 mm. In their lowest adjustment position, adjustable 
head restraints must not be lower than 750 mm, and in their highest 
position, they must be at least 800 mm. To reduce the distance that a 
vehicle occupant's head can be whipped backward in a rear end crash, 
this rule established new requirements limiting backset in front seats 
and limiting the size of gaps and openings in the restraints. The rule 
also established new strength and position retention requirements. 
Finally, it significantly amended the dynamic compliance test option 
currently in the standard to

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encourage continued development and use of ``active'' head restraint 
systems because the test is designed to allow a manufacturer the 
flexibility necessary to offer innovative active head restraint designs 
while still ensuring a minimal level of head restraint performance.
    In developing the final rule, the agency decided not to require 
head restraints for rear seating positions. However, in order to ensure 
that head restraints voluntarily installed in rear outboard seating 
positions do not pose a risk of exacerbating whiplash injuries, the 
final rule required that, if provided, those head restraints meet 
certain height, strength, position retention, and energy absorption 
requirements, but no backset limit. The head restraint regulation of 
the United Nations/Economic Commission for Europe (UN/ECE) also does 
not mandate rear seat head restraints, but manufacturers can 
voluntarily choose to have rear head restraints type approved per the 
regulation.
    The agency explained that in the future stages of its efforts to 
improve occupant protection in rear impacts, it intends to evaluate the 
performance of head restraints and seat backs as a single system to 
protect occupants, just as they work in the real world, instead of 
evaluating their performance separately as individual components. 
Accordingly, in making our decisions about the upgraded requirements 
for head restraints, we sought, e.g., through upgrading our dynamic 
test procedure option, to make those requirements consistent with the 
ultimate goal of adopting a method of comprehensively evaluating the 
seating system.
    NHTSA also sought to harmonize the FMVSS requirements for head 
restraints with the head restraint regulation of the UN/ECE, except to 
the extent needed to provide increased safety for vehicle occupants or 
to facilitate enforcement.\14\ In some instances, a desire to achieve 
increased safety in a cost effective manner made it necessary for us to 
go beyond or take an approach different from that in the ECE 
regulation.
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    \14\ The regulation, adopted by the UN/ECE's Working Party 29, 
World Forum for Harmonization of Vehicle Regulations, is ECE 17, 
Uniform Provisions concerning the Approval of Vehicles with regard 
to the Seats, their Anchorages, and any Head Restraints (https://www.unece.org/trans/main/wp29/wp29regs/r017r4e.pdf).
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    The agency estimated that approximately 272,464 whiplash injuries 
occur annually, and that the final rule would result in approximately 
16,831 fewer whiplash injuries, 15,272 involving front seat occupants 
and 1,559 involving rear seat occupants. The estimated average cost in 
2002 dollars, per vehicle, of meeting the rule was estimated to be 
$4.51 for front seats, and $1.13 for rear seats currently equipped with 
head restraints, for a combined cost of $5.42. The cost per year was 
estimated to be $70.1 million for front head restraints and $14.1 
million for optional rear head restraints, for a combined annual cost 
of $84.2 million. The final rule was considered to be economically 
significant because the agency estimated that it would result in 
economic benefits in excess of $100 million.
2. Details of the December 2004 Final Rule
    Under the final rule, the top of the front outboard integral head 
restraint must reach the height of at least 800 mm above the H-point, 
instead of the 700 mm above the seating reference point (SgRP) \15\ 
previously required. The top of the front outboard adjustable head 
restraint must be adjustable to at least 800 mm above the H-point, and 
cannot be adjusted below 750 mm.
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    \15\ The term ``seating reference point'' is fully defined in 49 
CFR 571.3. It represents a unique design H-point. The H-point is the 
mechanically hinged hip point of an SAE J826 (July 1995) three-
dimensional manikin (SAE J826 manikin), which simulates the actual 
pivot center of the human torso and thigh.
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    If a manufacturer chooses to install head restraints in rear 
outboard seating positions, these head restraints must meet certain 
height, strength, position retention, and energy absorption 
requirements. The rear outboard head restraint is defined as a rear 
seat back, or any independently adjustable seat component attached to 
or adjacent to the rear seat back, that has a height equal to or 
greater than 700 mm, in any position of backset and height adjustment, 
as measured with the J826 manikin. Accordingly, any rear outboard seat 
back or any independently adjustable component attached or adjacent to 
that seat back that exceeds 700 mm above the H-point, must meet the 
above requirements.
    In recognition of the manufacturing and measurement variability 
concerns highlighted by the industry commenters, the agency increased 
the maximum allowable backset for front head restraints from the 
proposed 50 mm to 55 mm. Backset adjustment to less than 55 mm was 
permitted. However, the backset may not be adjustable to greater than 
55 mm when the top of the front head restraint is positioned between 
750 and 800 mm, inclusive, above the H-point. There is no backset limit 
for optional rear head restraints. The agency specified use of a Head 
Restraint Measurement Device (HRMD), consisting of a head form 
developed by the Insurance Corporation of British Columbia (ICBC) 
attached to the Society of Automotive Engineers (SAE) J826 manikin 
(rev. Jul 95), for measuring backset compliance.
    The minimum width requirement for front outboard head restraints in 
vehicles without a front center seating position, and for optional rear 
head restraints is 170 mm. The minimum width requirement for front 
outboard head restraints in vehicles with a center seating position 
between the outboard positions is 254 mm. For integral head restraints, 
there is a limit of 60 mm on the maximum gap between the head restraint 
and the top of the seat. The gap limit for adjustable head restraints 
in their lowest position of adjustment and any position of backset 
adjustment is similarly 60 mm. For all head restraints, gaps within the 
restraint are also limited to not more than 60 mm.
    Under the final rule, an adjustment retention mechanism that locks 
into place is mandatory for all adjustable head restraints. Retention 
of the head restraint in its vertical position is tested using a 
loading cylinder measuring 165 mm in diameter and 152 mm in length. The 
rearward (with respect to the seat direction) position retention 
testing is conducted using a loading sphere, with the seat back braced. 
Under both tests, the head restraint must return to within 13 mm of the 
initial reference point, an increase from the proposed 10 mm return 
requirement.
    The energy absorption test procedure is conducted using a linear 
impactor, rather than the proposed free-motion impactor or the pendulum 
impactor used in ECE 17.
    The dynamic compliance option utilizes a Hybrid III 50th percentile 
adult male test dummy only, as the 95th percentile Hybrid III dummy is 
not yet available for compliance purposes. The head-to-torso rotation 
is limited to 12 degrees, and the maximum HIC15 was limited 
to 500 instead of 150 in the NPRM. These performance limits must be met 
with the head restraint midway between the lowest and the highest 
position of adjustment rather than at the lowest position as proposed.
    Between the effective date of the final rule and September 1, 2008, 
manufacturers were permitted to comply with FMVSS No. 202 by meeting: 
(1) All the requirements of the current FMVSS No. 202, (2) the 
specified requirements of ECE 17, or (3) all the requirements of FMVSS 
No. 202a. NHTSA has found that ECE 17 is functionally equivalent to the 
existing FMVSS No. 202, so it permitted

[[Page 25488]]

compliance with ECE 17 during the interim.

II. Petitions for Reconsideration

    We received seven petitions for reconsideration. Four were from 
auto manufacturers or an auto manufacturer trade association: the 
Alliance of Automobile Manufacturers (Alliance), Ford, DaimlerChrysler, 
and BMW. Two were from seat manufacturers: Johnson Controls and Keiper. 
The seventh petition was submitted by Syson-Hill and Associates, an 
engineering services firm. We note that we also received a petition 
from Kongsberg Automotive. However, since this was not submitted within 
the required timeframe for petitions for reconsideration, our 
regulations provide that it is treated as a petition submitted under 49 
CFR part 552, rather than a petition for reconsideration. We address 
this petition for rulemaking in a separate section at the end of this 
notice.
    In this section, we provide a brief summary of the issues raised by 
the petitions. The summary is representative and does not necessarily 
identify each petitioner which raised a particular issue.

A. Backset Requirement

    Several petitioners asked the agency to reconsider the 55 mm 
backset requirement. The Alliance stated that it believes there are 
potential safety disbenefits from the requirement. It argued that the 
55 mm backset requirement measured at 25 degree torso angle is too 
aggressive and will create significant dissatisfaction. The Alliance 
stated that while it agrees less backset is better, a better balance 
between customer comfort and safety benefits must be achieved. It 
requested a maximum 70 mm requirement with ``a 10 mm audit allowance to 
80 mm.''
    DaimlerChrysler stated that it firmly believes that the backset 
requirement for front seats is overly restrictive and should be 
relaxed. That company stated that its experience suggests that designs 
meeting this requirement will encounter very strong consumer 
resistance. DaimlerChrysler stated that it designed the head restraints 
for a new vehicle to meet the backset requirements included in the 
NPRM, i.e., 50 mm at a torso angle of 25 degrees. It stated that 
consumer reaction from some customers, especially short-statured 
drivers, was very negative, and that some have removed or reversed the 
head restraint.
    Daimler Chrysler asked the agency to reconsider the 25 degree torso 
angle as well as the 55 mm limit. That company stated that there are 
several vehicle concepts, including light trucks, in which an angle of 
25 degrees is much greater than the design and not realistic, thus 
leading to a much larger backset measured in the specified procedure as 
compared to a real world situation. DaimlerChrysler recommended that 
the agency specify the ``design torso angle'' rather than 25 degrees.
    Johnson Controls stated that it believes a 90 mm backset 
requirement would best accomplish the goals of safety and passenger 
comfort while recognizing the practical effects of design and 
measurement variation inherent in the backset measurement technology.

B. Backset Measurement Method

    Ford argued that the backset measurement method and device 
specified in the final rule have not been sufficiently evaluated to 
adequately account for total process variability. It stated that test 
data analysis shows that the actual variability far exceeds the amount 
specified in the final rule, and that the rule is therefore not 
reasonable or practicable.

C. Dynamic Option

    The Alliance stated that it believes the dynamic test alternative 
included in the final rule is premature and not adequately supported 
and developed for use at this time. It requested that the agency 
investigate other alternatives and, in the meantime, retain the 
existing dynamic test in FMVSS No. 202.

D. Rear Seat Non-Use Positions

    Petitioners for reconsideration asked the agency to make several 
changes in the requirements for rear seat non-use positions. The 
Alliance and Ford petitioned the agency to allow head restraint designs 
that manually retract (without having to rotate) to non-use positions 
and that must be manually repositioned to in-use positions. The 
Alliance, BMW and DaimlerChrysler requested that the manually stowed 
non-use position compliance option originally in the NPRM be reinstated 
except that the required torso angle change should be no more than 5 
degrees. GM recommended several options for visual cues to indicate 
that a rear seat head restraint is in a non-use position.

E. Effective Date

    The Alliance stated that while the date set forth in the final rule 
appears to provide more than three years leadtime, it was concerned 
that that leadtime will be subsumed during the period petitions for 
reconsideration are before the agency. It argued that additional 
leadtime could be needed depending on when the agency resolved issues 
raised in the petitions. The Alliance also requested that in order to 
permit manufacturers to implement the required changes with the start 
of a new model cycle rather than at the end of the current model 
design, NHTSA should modify the compliance date to require 80 percent 
compliance with FMVSS No. 202a for the first year and 100 percent 
beginning the second year, with carry-forward credits.

F. Other Issues

    The petitioners for reconsideration raised a number of other 
issues, including ones related to the height requirement, gaps between 
the head restraint and the seat back, the backset and height retention 
(lock) tests, the energy absorption test and seat back bracing, head 
restraint clearance, the width of head restraints for certain seats, 
the option to comply with ECE 17, temperature and humidty, and owner's 
manual requirements.

III. Development of Global Technical Regulation on Head Restraints

    For the past couple years, NHTSA has been leading efforts to 
develop a Global Technical Regulation (GTR) on head restraints. During 
the November 2004 meeting of WP.29 and the Executive Committee of the 
1998 Global Agreement, NHTSA formalized its sponsorship of the 
regulation on Head Restraints as identified in the Program of Work of 
the 1998 Global Agreement. In a notice published in the Federal 
Register (69 FR 60460) on October 8, 2004, NHTSA sought comments on a 
proposal that formalizes the U.S. sponsorship of a GTR on head 
restraints. The agency did not receive any comments.
    The proposal was formally presented by the U.S. and adopted by the 
Executive Committee and referred to the Working Party of Experts (GRSP) 
at the March 2005 Session of WP.29. In February 2005, the GRSP formed 
an informal working group, chaired by the US, to develop a GTR. The 
working group has met eight times with the following contracting 
parties and representatives participating: Netherlands, France, Canada, 
Japan, Germany, Spain, Korea, the UK, USA, the EC, the European 
Association of Automotive Suppliers (CLEPA) and the International 
Organization of Motor Vehicle Manufacturers (OICA).
    In developing and drafting the new GTR, the working group is 
combining elements from UNECE Regulations Nos. 17, 25, and newly 
upgraded FMVSS No. 202, as well as considering proposals for

[[Page 25489]]

requirements not contained in the previously mentioned regulations. The 
working group is exchanging data and has started drafting the 
regulatory text.
    The major outstanding issues are:
     Applicability: Applying the GTR to vehicles up to 4,500 kg 
or limiting it to 3,500 kg.
     Backset: There is general consensus that it should be 
regulated, but the maximum backset limit is still being discussed.
     Measuring procedures for height and backset: There is 
continued discussion on using the H-point or R point as the point of 
reference.
     Dynamic Test: The issue of how to evaluate dynamic systems 
continues to be under discussion.
    The working group has submitted four Progress Reports on the status 
of this GTR. They can be found in Docket No. NHTSA-2004-14395.
    We note that the work on the GTR has been proceeding at the same 
time that NHTSA has been evaluating the petitions for reconsideration. 
Some of the issues that are the subject of the petitions for 
reconsideration have also been raised in the context of the GTR. In 
this document, we are addressing those issues in the context of the 
petitions for reconsideration of the recently upgraded FMVSS No. 202. 
If the development of the GTR continues to proceed successfully and it 
is ultimately adopted, and if the U.S. has voted for its adoption, 
NHTSA would issue an NPRM based on the GTR for a new FMVSS.

IV. March 2006 Partial Response to Petitions

    On March 9, 2006, NHTSA published in the Federal Register (71 FR 
12145) a final rule; partial response to the petitions for 
reconsideration.\16\ In that document, the agency delayed the date on 
which manufacturers must comply with the requirements applicable to 
head restraints voluntarily installed in rear outboard designated 
seating positions from September 1, 2008 until September 1, 2010. The 
agency stated that the remaining issues raised by petitioners for 
reconsideration would be addressed in a separate document.
---------------------------------------------------------------------------

    \16\ Docket No. NHTSA-2006-23848.
---------------------------------------------------------------------------

V. Overview of Decision

    This document addresses the remaining issues raised by petitioners 
for reconsideration of the December 2004 final rule upgrading the 
agency's head restraint standard. We are partially granting and 
partially denying the petitions. The more significant changes that we 
are making in response to the petitions include:
     Leadtime: For the front seat requirements, we have decided 
to provide one additional year of leadtime and also establish a one-
year phase-in with an 80 percent requirement. The agency previously 
extended the compliance date for the rear seat requirements by two 
years. We are also establishing a one-year phase-in with an 80 percent 
requirement for the rear seat requirements.
     Backset: We are making two changes related to the backset 
requirement. First, we are specifying in FMVSS No. 202a that backset is 
determined by taking the arithmetic average of three measurements, 
rather than using a single measurement. Two studies, one by NHTSA and 
one by Transport Canada, have indicated that taking an average of 
several measurements reduces variability. Second, we are slightly 
relaxing the backset requirement by specifying that the 55 mm backset 
limit applies with the seat back at the vehicle manufacturer's 
specified design angle rather than at 25 degrees. This decision 
reflects consideration of interrelated issues and data concerning the 
55 mm backset limit, comfort, and seat back angle.
     Rear Seat Non-Use Positions: To provide greater 
flexibility in this area, we are adding (as included in the NPRM) an 
option for a 10-degree change in the torso reference angle criteria.
     Gaps Between Head Restraint and Seat Back: We are adding a 
manufacturer option under which the gap requirement may be met by 
either the existing FMVSS No. 202a procedure using a sphere or one 
based on the ECE 17 measurement methodology.
     Backset and Height Retention (Lock) Tests: We are 
specifying that instead of returning to the reference loads of 37 Nm 
and 50 N after application of the peak load during these tests, that 
the load be reduce to zero and then increased to the reference loads.
    As discussed in the sections which follow, we are making a number 
of other changes as well.
    Finally, as indicated above, the agency has separately been leading 
efforts to develop a GTR on head restraints. Some issues raised by 
petitioners for reconsideration, including ones related to backset and 
the dynamic test, are also being discussed in the context of the GTR. 
While it is necessary for us to issue today's decision in order to 
respond to the outstanding petitions for reconsideration, we note that 
if agreement is achieved on the GTR, we will consider making changes in 
these and other areas.

VI. Response to Petitions

A. Backset Requirement

1. Petitions
    Several petitioners, including automobile manufacturers and seat 
manufacturers, requested reconsideration of the 55 mm backset 
requirement.
    Under the final rule, backset is measured using an HRMD consisting 
of a head form developed by ICBC attached to the SAE J826 manikin (rev. 
Jul 95). The head form includes a probe that slides rearward until 
contact is made with the head restraint. The resulting measurement 
reflects the horizontal distance between the back of the head of a 
seated 50th percentile adult male occupant and the front of the head 
restraint.
    Under the final rule, backset must not exceed 55 mm for front 
seats, with the seat back positioned at an angle that gives the J826 
manikin a torso reference line angle of 25 degrees. We will refer to 
the torso reference line angle and seat back angle interchangeably.
    In addressing the petitioners' requests concerning the backset 
requirement, we will consider together issues related to the 55 mm 
value, test procedure variability, specification of the HRMD, and seat 
back angle, as they are closely interrelated.
    The Alliance stated that it believes that the 55 mm backset 
requirement measured at 25 degree torso angle is too aggressive and 
will create significant customer dissatisfaction. It stated that while 
it agrees that reducing backset is desirable, a better balance between 
customer comfort and safety benefits should be achieved. That 
organization stated that 5th percentile female stature occupants do not 
sit at 25 degree torso angles, but prefer about 18 degrees and some as 
little as 14 to improve their ability to see the road ahead.
    The Alliance stated that this is corroborated by the 2001 UMTRI 
response to the NPRM, which indicates a mean seat back (torso angle) of 
22 degrees with a 3.2 degree standard deviation. The petitioner argued 
that this more upright back angle greatly reduces the backset to the 
point it interferes with the head of some of these occupants, if not 
just their hair.
    (NHTSA notes that backset is reduced with more upright seat back 
angles because the angle of an occupant's head relative to the 
occupant's torso changes as the occupant's seat back angle is changed. 
As an occupant's seat back

[[Page 25490]]

angle is reduced, making the seat back more vertical, the occupant's 
head is tilted increasingly further back with respect to their torso. 
Conversely, as the back angle is increased, the occupant's head is 
tilted further forward.)
    The Alliance stated that negative consumer reactions to a recent 
new vehicle introduction with a 50 mm backset head restraint at 25 
degree torso angle included removal and reversal of the head restraint. 
That organization indicated that increasing the torso angle a couple 
degrees did not satisfy customers. The Alliance also stated that 
drivers' increasing the seat back angle to relieve the close proximity 
of the head restraint to their heads may result in positioning the seat 
back at an angle greater than the one that provides optimal vision of 
the vehicle controls and displays, headroom, and lumbar comfort.
    The Alliance stated that while the 50 mm backset requirement was 
relaxed to 55 mm in the final rule by NHTSA to account for a 5 mm 
measurement variability range of the HRMD, it does not account for a 2 
degree design tolerance for seat back torso angle or an H-point 
tolerance of 12 mm. The Alliance stated that it believes a maximum of 
70 mm should be adopted with a 10 mm audit allowance, making the limit 
effectively 80 mm. According to the Alliance, this would still make it 
necessary for manufacturers to design front head restraints within the 
IIHS Acceptable or Good rating for geometry.
    DaimlerChrysler stated that it firmly believes the backset 
requirement for front seats is overly restrictive and should be 
relaxed. That company stated that its experience suggests that designs 
meeting this requirement will encounter very strong consumer 
resistance. It made a number of the same arguments as the Alliance, in 
some cases in more detail.
    DaimlerChrysler indicated that it recently introduced a new vehicle 
in the U.S. market that was designed just after the issuance of the 
NPRM for the head restraint rule. That company stated that it 
ambitiously designed the head restraints for this new vehicle to meet 
the backset requirements of the NPRM, i.e., 50 mm at a torso angle of 
25 degrees. DaimlerChrysler stated that the reaction from some 
customers has been very negative, with more than two percent of 
customers rating them unacceptable in a recent survey of owners. That 
company stated that given this response, it embarked on a high priority 
redesign effort to change the backset to 65 mm at a 25 degree torso 
angle.
    According to DaimlerChrysler, it appears that a high percentage of 
5th percentile female drivers object to the head restraints. It stated 
that some of these drivers are removing the head restraint and others 
are reversing the head restraint. DaimlerChrysler also stated that 
merely reclining the seat further has not been an acceptable solution 
for some drivers (especially those of short stature), and could also 
degrade visibility of controls, displays and rearward visibility.
    DaimlerChrysler also stated that studies by the IIHS conclude that 
women are at greater risk of neck injury than men. That company argued 
that a new head restraint standard should protect those at the greatest 
risk, where the benefits are greatest, and where discomfort issues have 
the greatest consequences. DaimlerChrysler argued that referencing the 
backset requirement from a 25 degree torso angle, an angle more 
consistent with the angles typically used by larger stature (i.e., 
taller) occupants than those used by smaller stature occupants biases 
the requirement in favor of the larger stature occupants at the expense 
or discomfort of smaller stature occupants.
    DaimlerChrysler stated that the UMTRI submission in response to the 
NPRM showed mean seat back angles to be 22.5 degrees with a standard 
deviation of 3.5 degrees. According to DaimlerChrysler, the mean angle 
minus 2 standard deviations approximates the 5% female occupant and the 
mean angle plus 2 standard deviations approximates the 95% male 
occupant. It stated that this shows, on average, a 14 degree range in 
seat back angle between these upper and lower size occupants for 
automotive design. DaimlerChrysler stated that with NHTSA's assumed 3 
mm change in backset per degree change in seat back angle, most of the 
55 mm backset is lost for the 5% female without any accommodation for 
hair clearance. DaimlerChrysler suggested that the regulation specify 
the backset at the seat back design angle.
    DaimlerChrysler provided other arguments in support of specifying 
backset at the seat back design angle. It argued that there are several 
vehicle concepts (e.g., light trucks, minivans, SUV's and full size 
vans) in which an angle of 25 degrees is not realistic, thus leading to 
a much larger backset in NHTSA's procedure as compared to the real 
world situation. That company stated that SAE J-1100 July 2002 
recommends a 22 degree nominal torso design angle. It urged the agency 
to use the ``design torso angle.''
    In a later submission, DaimlerChrysler indicated that nominal seat 
back angles for high vehicles, e.g., light trucks, are approximately 20 
degrees, whereas for other vehicles, e.g., sedans they are 
approximately 23 to 25 degrees. It indicated that a 1 degree increase 
of seat back angle yields 3 to 4 mm increase of backset.
    On the issue of the 55 mm backset limit and variability, 
DaimlerChrysler stated that while the final rule made some 
accommodation for measurement variance for the HRMD, the net effect of 
the 55 mm backset limit is less than a 50 mm backset design. It argued 
that the 5 mm increase that NHTSA included in the final rule does not 
account for seat back (torso angle) tolerances that are 2 
degrees, and H-point tolerances of 12 mm. In a later 
submission, DaimlerChrysler argued that a ``worst case'' sum of backset 
tolerances is 29 mm. This includes 5 mm for seat upholstery, 10 mm for 
torso angle of the manikin, 10 mm for head rest rod to seat back angle, 
and 4 mm for seat reference point. DaimlerChrysler indicated that it 
would be necessary to design to a 26 mm backset limit to allow for 
these worst case tolerances.
    DaimlerChrysler stated that all of its arguments point to the need 
for greater backset, and an audit allowance of at least a 10 mm beyond 
the intended nominal requirement. It requested a nominal backset 
requirement of 70 mm, with an additional 10 mm allowance for 
compliance.
    DaimlerChrysler characterized NHTSA's philosophy in the head 
restraint rulemaking as being ``if a little backset is good, less is 
better,'' and argued such an approach cannot be justified below 70 mm 
of backset. That company stated that it agreed that, all things being 
equal, ``the less the backset, the better,'' but a balance between 
``customer acceptance'' and ``a better theoretical design'' should be 
achieved. DaimlerChrysler argued that until the mechanism and threshold 
for whiplash is completely understood, overly ambitious targets should 
be avoided until they can be backed by better fundamental knowledge of 
the causation and prevention of rear impact induced neck injuries and 
customer acceptance.
    Ford stated that it believes the backset measurement method and 
device have not been sufficiently evaluated to account adequately for 
total process variability. It stated that its test data analysis found 
significantly greater operator/gauge variability than that suggested by 
the agency in its rule.
    Ford argued that the capability of the HRMD and related measurement 
process has not been sufficiently established. That company stated that 
the final rule preamble stated that

[[Page 25491]]

``maximum allowable backset requirement is based on the 5 
mm tolerance of the measuring device'' and that the tolerance 
``represents the variability associated with measuring backset with the 
ICBC measuring device.'' Ford argued that this statement does not 
define in acceptable statistical terms the accuracy of the measuring 
device and that sufficient data are not provided to permit an 
assessment of the accuracy of the measuring device.
    Ford argued that, as a threshold matter, the accuracy of the 
measuring device must be determined. It asserted that accuracy 
characterizes the level of deviation of the measurement device output 
from known ``accurate'' values, and that accuracy evaluation is 
performed utilizing calibration procedures using established certified 
specimens that are traceable to nationally recognized standards 
typically maintained by the National Institute of Standards & 
Technology. Ford claimed that without such traceability it is 
impossible to evaluate ICBC's claim that ``that the HRMD yields a level 
of accuracy of 5 mm when used by competent, well-trained 
operators.''
    Ford stated that RONA Kinetics, the developer and manufacturer of 
the HRMD,\17\ calibrates all new HRMDs, but there are no studies to 
indicate how well that calibration is maintained over time in various 
test labs. According to Ford, there is no calibration procedure that 
test labs can use to check calibration retention. It argued that 
because the true accuracy of HRMDs is not known, seat manufacturers and 
agency contractors cannot reliably verify compliance with the backset 
requirement of 55 mm. Ford argued that the agency should develop the 
accuracy requirements for the HRMD, verify that the proposed HRMDs 
satisfy these minimum requirements, and develop calibration standards 
and the necessary equipment to permit periodic calibration of the test 
device at the point of use.
---------------------------------------------------------------------------

    \17\ We note that some commenters refer to the ICBC device as 
HRMD, whereas the agency refers to the combined ICBC device and J826 
manikin as the HRMD.
---------------------------------------------------------------------------

    Ford stated that once accuracy and calibration are established, 
repeatability and reproducibility as well as other major variability 
factors should be assessed with a study. According to that company, a 
comprehensive study should be conducted to assess the statistical 
distribution of the backset measurement on a sufficient sample of seat 
designs representative of the United States light vehicle fleet and 
these measurements should be compared to the actual backset. Ford 
stated that these variables include, but are not limited to, different 
HRMD machines, different J826 manikins, different operators, different 
laboratories, differing temperatures and humidity, as well as the 
variability of the parameters set forth in the agency's compliance test 
procedure.
    Ford stated that in the absence of these data, it undertook a 
preliminary study to assess the accuracy of the HRMD. According to 
Ford, this study did not attempt to evaluate all major sources of 
potential variability. The preliminary study evaluated three different 
seats designed to meet the IIHS good rating, and used three trained 
operators using their own HRMD and associated J826 manikins.
    Ford stated that of five combinations it evaluated, only one 
combination across three paired operators/gauges had a range of 10mm. 
The remaining combination ranges were between 19 mm and 21 mm. Ford 
stated that if it assumed that the 5 mm ``tolerance'' 
represents a range of 10 mm, these results double what the agency 
stated manufacturers should expect when measurements are taken by 
trained HRMD operators.
    Ford also stated that this study excluded certain significant 
potential variables, including the impact of various laboratories, 
temperature and humidity variances, and manufacturing variability. Ford 
argued that its study identifies the need for the agency to perform the 
necessary work to determine the actual capability of the HRMD, and that 
the agency needs to consider and address other potential sources of 
variability and develop a reasonable and practicable backset 
requirement.
    Ford also submitted data which it argued indicated that multiple 
variabilities mean that head restraint designs must use a backset less 
than 30 mm to assure statistical significance.
    Ford later submitted the results of two studies addressing comfort 
and backset. That company stated that the studies show that it is not 
possible to design a seat that is both statistically compliant with the 
55 mm requirement and comfortable for a vast majority of drivers. That 
company argued that the data show that the design target must be less 
than 19 mm to be compliant statistically with the 55 mm requirement. It 
also stated that the minimum backset required to satisfy 85 percent of 
drivers is 69 to 87 mm, depending on the vehicle model. Ford argued 
that for head restraints that do not adjust in the fore/aft direction, 
the FMVSS 202a backset requirement would have to be at least 98 mm in 
order to satisfy about 85 percent of drivers. Ford stated that fore/aft 
adjustable head restraints could be a solution to the comfort problem 
if FMVSS 202a permitted the 55 mm backset requirement at the most 
forward position of the head restraint.
    Johnson Controls stated that it believes a 90 mm backset 
requirement would best accomplish the goals of safety and passenger 
comfort while recognizing the practical effects of design and 
measurement variation inherent in the backset measurement methodology. 
It stated that an UMTRI study concluded that backset below 70 mm would 
not accommodate a substantial number of occupants. Johnson Controls 
also argued that the potential for variation in measurement technique 
and the variation inherent in the design tolerances associated with the 
determination of backset require a substantially lower nominal backset 
than the 55 mm limit in the standard. That petitioner noted that the 
agency added 5 mm in light of variability associated with the measuring 
device, but argued that while this is one facet of variation, sources 
of variation include repeatability, reproducibility, trim, foam and 
structure tolerances that are inherent in the designs used.
2. Agency Response
    In responding to the petitions concerning the backset requirement, 
we begin by noting that the agency addressed issues related to backset 
at considerable length in the final rule preamble. As discussed in that 
document, in selecting the 55 mm limit, we attempted to balance 
comfort, safety and measurement variability concerns.
    While all of these concerns are important, we note that in order to 
address the problem of whiplash, it is necessary to reduce the backset 
of many current head restraints. As discussed in the final rule, the 
available scientific data show that whiplash may be caused by 
relatively small amounts of head and neck movements relative to the 
torso.
    Based on the available scientific data, NHTSA estimated that the 
final rule, once fully implemented, would prevent 15,272 front seat 
whiplash injuries annually. By contrast, we estimate that if the 55 mm 
backset limit were relaxed to 70 mm, the number of prevented injuries 
would be reduced by almost half, to 7,743. In the final rule preamble, 
we noted that no commenter disputed scientific data indicating that the 
closer the head restraint is to the occupant's head at the time of 
impact, the better the protection the head restraint offers.

[[Page 25492]]

    On reconsideration, for reasons discussed below, we have decided to 
make two changes related to the backset requirement. First, we are 
specifying in FMVSS No. 202a that backset is determined by taking the 
arithmetic average of three measurements, rather than using a single 
measurement. Two studies, one by NHTSA and one by Transport Canada, 
have indicated that taking an average of several measurements reduces 
variability. Second, we are slightly relaxing the backset requirement 
by specifying that the 55 mm backset limit applies with the seat back 
at the vehicle manufacturer's specified design angle rather than at 25 
degrees. This decision reflects consideration of interrelated issues 
and data concerning the 55 mm backset limit, comfort, and seat back 
angle.
    In explaining our decision in this area, we will begin with a 
discussion of issues related to suitability of the HRMD. We will then 
address issues related to comfort, seat back angle, and the 55 mm 
backset limit.
a. Suitability of the HRMD and Measurement Variability
    In the final rule preamble, we addressed issues related to 
specifying use of the HRMD for measuring backset and test variability. 
As discussed earlier, the agency relaxed the backset requirement from 
the proposed 50 mm by 5 mm, to 55 mm, to account for the variability 
associated with measuring backset with the HRMD.
    The HRMD consists of a SAE J826 three-dimensional manikin with a 
head form designed by ICBC attached. The SAE J826 manikin is sometimes 
referred to as an ``OSCAR'' device. The ICBC head form includes a probe 
that slides rearward until contact is made with the head restraint, 
thereby measuring backset.
    In commenting on the NPRM, most vehicle manufacturers and seat 
suppliers had opposed the use of the HRMD. Generally, they questioned 
the accuracy and repeatability of head restraint geometry measurements 
made using that device. Further, the HRMD was deemed too sensitive to 
foam, trim, actual H-point, temperature, and humidity variations. 
Several commenters argued that the HRMD was not appropriate for 
compliance testing because repeated testing on the same seat assembly 
yielded different results. For example, Ford noted that the 2000 Ford 
Taurus and 2000 Mercury Sable received different ratings despite the 
fact that they are manufactured on the same platform and have identical 
front seats.
    On the other hand, Transport Canada had reported that a study 
commissioned by several Canadian insurance companies, conducted by RONA 
K