Federal Motor Vehicle Safety Standards; Head Restraints

Federal RegisterDec 14, 2004

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. NHTSA-2004-19807]

RIN 2127-AH09

Federal Motor Vehicle Safety Standards; Head Restraints

AGENCY:

National Highway Traffic Safety Administration (NHTSA), DOT.

ACTION:

Final rule.

SUMMARY:

This final rule upgrades NHTSA's head restraint standard in order to reduce whiplash injuries in rear collisions. For front seats, the rule establishes a higher minimum height requirement, a requirement limiting the distance between the back of an occupant's head and the occupant's head restraint, as well as a limit on the size of gaps and openings within head restraints. The rule also establishes new strength and dynamic compliance requirements, and amends most existing test procedures. In addition, the rule establishes requirements for head restraints voluntarily installed in rear outboard designated seating positions. The upgraded standard becomes mandatory for all vehicles manufactured on or after September 1, 2008. Until that time, the manufacturers may comply with the existing NHTSA standard, the upgraded NHTSA standard or the current European regulations.

DATES:

Effective Date:

This rule is effective March 14, 2005.

Incorporation by reference:

The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of March 14, 2005.

Petitions:

Petitions for reconsideration must be received by January 28, 2005.

ADDRESSES:

Petitions for reconsideration should refer to Docket No. NHTSA-2004-19807 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@nhtsa.dot.gov

For legal issues, you may contact George Feygin of the Office of Chief Counsel, NCC-112, (Phone: (202) 366-2992; Fax (202) 366-3820; E-mail:

George.Feygin@nhtsa.dot.gov

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. Executive Summary

II. Background

a. The Safety Concern

b. Understanding Whiplash

III. Notice of Proposed Rulemaking

IV. Summary of Comments on the NPRM

V. Summary of the Final Rule

VI. Height and Width Requirements

a. Requirements for Front Seats

b. Requirements for Rear Seats Equipped with Head Restraints

VII. Backset Requirements for Front Seats

VIII. Measurement of Backset and Height

IX. Maximum Gap Allowance and Removability

a. Maximum Gap Allowance

b. Removability

c. Non-use Positions

X. Position Retention

XI. Energy Absorption

XII. Issues Unique to Rear Head Restraints

a. Optional Head Restraints for Rear Seating Positions

b. Exception for Seats Adjacent to an Aisle

c. Potential Interference with Child Restraints and Tethers

XIII. Dynamic Test Alternative

XIV. Consumer Information

XV. Effective Date and Interim Compliance Options

XVI. Costs and Benefits Associated with the Final Rule

XVII. Rulemaking Analyses and Notices

a. Executive Order 12866 and DOT Regulatory Policies and Procedures

b. Regulatory Flexibility Act

c. National Environmental Policy Act

d. Executive Order 13132 (Federalism)

e. Unfunded Mandates Reform Act

f. Executive Order 12988 (Civil Justice Reform)

g. Paperwork Reduction Act

h. Executive Order 13045

i. National Technology Transfer and Advancement Act

j. Privacy Act

Appendix A: Efforts to Harmonize with ECE 17

Appendix B: Cervigard Suggestion

I. Executive Summary

This final rule upgrades Federal Motor Vehicle Safety Standard No. 202,

Head Restraints

(FMVSS No. 202). The standard, which seeks to reduce whiplash injuries in rear collisions, currently requires head restraints for front outboard designated seating positions in passenger cars and in light multipurpose passenger vehicles, trucks and buses.

To provide better whiplash protection for a wider range of occupants, this rule requires 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 establishes new requirements limiting backset in front seats,

i.e.

, the distance between the back of a person's head and his or her head restraint, and limiting the size of gaps and openings in the restraints. The rule also establishes new strength and position retention requirements. Finally, it significantly amends the dynamic compliance test option currently in the standard to 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.

After a careful consideration of the public comments and further analysis of our proposal to require head restraints in each rear outboard designated seating position, we have decided not to adopt that proposal. In the Notice of Proposed Rulemaking (NPRM),

we expressed concern that the proposal had a high cost per equivalent life saved. We have now made a more refined estimate of costs and benefits and found that the cost per equivalent life saved for such a requirement is even greater than originally thought. In response to the NPRM, several manufacturers raised visibility concerns associated with mandatory rear head restraints in all vehicles. While not a universal problem, we believe reduced visibility is a legitimate problem in some vehicles. Finally, in commenting on the NPRM, vehicle manufacturers expressed concern that adoption of the requirement would reduce vehicle utility by interfering with or even reducing the ability to provide the sort of folding seats currently available in “multi-configuration” vehicles such as vans and multipurpose vehicles. We believe that those concerns may have some merit.

See

66 FR 968 (January 4, 2001).

However, in order to ensure that head restraints voluntarily installed in rear outboard seating positions do not pose a risk of exacerbating whiplash injuries, this final rule requires that those head restraints meet certain height, strength, position retention, and energy absorption requirements. NHTSA notes that the head restraint regulation of the United Nations/Economic Commission

for Europe (UN/ECE) similarly does not mandate rear seat head restraints, but does regulate the performance of voluntarily installed ones. The ECE regulation is discussed at greater length several paragraphs below and in Appendix A.

In the future stages of our efforts to improve occupant protection in rear impacts,

NHTSA 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 in this final rule, 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.

As part of this effort, NHTSA issued a final rule upgrading the performance of vehicle fuel systems in rear impacts. (68 FR 67068, December 1, 2003).

This final rule harmonizes 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.

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.

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 (

http://www.unece.org/trans/main/wp29/wp29regs/r017r4e.pdf

). A comparison of this final rule with ECE 17 is in Appendix A.

While some of the requirements of this final rule are more stringent than those of the ECE regulation, the latter is functionally equivalent to the current FMVSS No. 202.

For this reason, in the interim before the mandatory compliance date of this rule (September 1, 2008), the agency is giving manufacturers the option of complying with any of three alternatives: the existing FMVSS No. 202, the ECE 17, or the new, upgraded FMVSS No. 202, designated as FMVSS No. 202a.

We determined that the current FMVSS No. 202 is functionally equivalent to the applicable ECE regulation using the method described in Appendix B of 49 CFR part 553.

Once the FMVSS No. 202a becomes fully effective on September 1, 2008, it will be re-designated as FMVSS No. 202.

The agency estimates that approximately 272,464 whiplash injuries occur annually. This final rule will 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 this rule will 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 is 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. This final rule is economically significant because we estimate that the final rule will result in economic benefits in excess of $100 million.

Because this rule does not require head restraints in rear outboard designated seating positions, it does not impose any costs associated with installing head restraints where none were previously installed.

II. Background

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 a two sliding metal shafts. Adjustable head restraints 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.

a. The Safety Concern

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 Analysis Sampling System (NASS) data, we estimate that between 1988 and 1996, 805,581 whiplash injuries

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.

Non-contact Abbreviated Injury Scale (AIS) 1 neck.

b. 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.

Previous regulatory approach.

As discussed in the NPRM preceding this 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.

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.

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.

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 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.

By contrast, another study showed significant increase in injury and duration of symptoms when occupant's head was more than 100 mm away from the head restraint at the time of the rear impact.

Jakobsson

et al., Analysis of Head and Neck Responses in Rear End Impacts—A New Human-Like Model.

Volvo Car Corporation Safety Report (1994).

Olsson

et al., An In-depth Study of Neck Injuries in Rear-end Collisions.

International IRCOBI Conference, pp 269-280 (1990).

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).

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.

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.

“

Effect of Head Restraint Position on Neck Injury in Rear Impact,

” World Congress of Whiplash-Associated Disorders (1999), Vancouver, British Columbia.

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 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 conclude 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 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.

III. Notice of Proposed Rulemaking

Using the new information gained about the effectiveness of head restraints, NHTSA published the NPRM for this final rule to improve on the effectiveness of head restraints. The continued persistence of high numbers of whiplash injuries indicated a need for the rulemaking.

The NPRM 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 is 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.

The current 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.

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 would have to reach the height of at least 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.

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). In addition, the NPRM also proposed maximum gap requirements for head restraints openings within the perimeter of the restraint, and for height adjustable head restraints, between the seat and head restraint. Head restraints must remain locked in specific positions after being set by the user.

254 mm (10 in) for restraints on bench-type seats, and 171 mm (6.75 in) for restraints on individual seats.

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

and the head restraint, and to remove the allowance for seat back failure.

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.

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.

Further, the NPRM proposed that the head restraints must have the same lateral width specified for statically tested restraints. Comments were requested on whether dynamically tested restraints should be subject to the width requirement or any of the other dimensional requirements used in the static test option.

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.

IV. Summary of Comments on the NPRM

The agency received approximately 50 comments on the NPRM, from motor vehicle manufacturers, seat suppliers, members of the engineering and research community, insurance companies, consumer groups, and governments and members of Congress. Overall, commenters supported upgrading FMVSS No. 202 while expressing concerns about and recommending changes to various proposals made in the NPRM.

A majority of the commenters generally supported the new height proposal, particularly as applied to head restraints for front seats. While few commenters had knowledge of any specific data regarding benefits of the proposed height increase, most commenters agreed that the new height requirement is potentially beneficial in reducing whiplash injury and had merit in harmonizing with ECE 17. Nonetheless, some concerns were expressed. Some comments supported the position that increasing the height of head restraints would not obstruct a driver's rearward visibility, but there were concerns expressed that the new height requirements would reduce the ability of a driver in following vehicles to “see through” a vehicle in front of him or her. There was concern that the taller head restraints could make it more difficult to install seats during vehicle assembly. Several manufacturers commented that the taller head restraints might not be able to fit in the rear seats of some vehicles or may impede seat folding, thus limiting cargo capacity.

As to the proposed width of head restraints, all of the vehicle manufacturers believed that a 254 mm width requirement for rear seat head restraints would reduce rearward visibility and is unwarranted. In contrast, Advocates for Highway Safety (Advocates) believed that the current widths of head restraints do not protect occupants in offset collisions and should be increased.

Commenters expressed differing opinions with regard to the proposed backset requirement. Insurers, consumer groups and Transport Canada supported 50 mm as the maximum allowable backset. A majority of the seat and vehicle manufacturers supported a backset of more than 50 mm, because they believed that a backset of 50 mm could result in occupant discomfort, particularly to smaller occupants who, commenters maintained, tend to use steeper seat back angles. Some manufacturers suggested that NHTSA allow for an adjustable backset of up to 100 mm. Manufacturers also generally wanted to measure backset with the seat back at the manufacturer's design seating angle rather than placed at a 25-degree angle. Some had concerns about the suitability of the head restraint measuring device for measuring backset.

There were no significant objections to the 60 mm gap limit for gaps within the perimeter of head restraints. However, manufacturers and others had questions about the proposal that adjustable head restraints in their lowest position must have some position of backset adjustment at which the gap between the seat and the head restraint is less than 25 mm.

A majority of industry commenters opposed the prohibition against the removability of head restraints. Some suggested allowing removability by hand, particularly of rear seat head restraints. Manufacturers stated that no limitations should be placed on non-use positions.

Several manufacturers and suppliers objected to the proposed height retention test requirement. Some believed current head restraints do not move downward during crashes. Others were concerned that the requirement does not account for the compression of head restraint foam. In contrast, some non-industry commenters believed that the height retention requirement is needed to prevent designs that tend to “fall” to their lowest position during normal vehicle operation.

With regard to the energy absorption test, all manufacturers suggested use of a pendulum impactor instead of the free-motion head form. Most manufacturers expressed concerns about the need for or wide-reaching application of the proposed limit on the radius of curvature of vehicle seats or head restraints (proposed S4.2(b)(8)).

Most manufacturers and suppliers believed that rear seat head restraints should not be required. Concerns were raised about the safety need for them, and about possible interference of the head restraints with child restraint use in rear seats. Honda, Advocates and others believed that rear seat head restraints should be mandated.

Concerning the proposed changes to the dynamic compliance test procedures, some commenters believed that the proposals should not be adopted at this time. Commenters disagreed on the most appropriate dummy to use for the dynamic test. Most vehicle manufacturers and some seat suppliers objected to the proposed HIC

150 limit, seeing no correlation between HIC and the reduction of neck injuries. Some commenters stated that the dynamic test should be with the seat attached to a test buck, instead of the actual vehicle.

In response to the NPRM's request for comments on the need to require vehicle manufacturers to provide

information in vehicle owners' manuals on how to properly adjust head restraints, the Insurance Corporation of British Columbia (ICBC) commented that it believed that consumer education has a positive influence on proper head restraint adjustment. Several manufacturers commented that most manufacturers already provide information in vehicle owners' manuals about proper head restraint use.

V. Summary of the Final Rule

Based on our consideration of the comments and other available information, the agency is issuing a final rule that upgrades existing FMVSS No. 202. As noted above, the new upgraded version of the standard is designated as FMVSS No. 202a.

Under this 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)

currently 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. Rear outboard head restraints are optional. However, 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.

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.

Exceptions to the height requirements for rear head restraints are discussed in Sections VI(b) and IX.

Section XII(a) explains how we arrived at our definition of rear head restraints.

In recognition of the manufacturing and measurement variability concerns highlighted by the industry commenters, the agency has increased the maximum allowable backset for front head restraints from the proposed 50 mm to 55 mm. Backset adjustment to less than 55 mm is 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 will use an HRMD, consisting of a head form developed by ICBC attached to the 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. The final rule does not adopt the proposed 25 mm limitation for adjustable head restraints in their lowest position of adjustment and single position of backset adjustment proposed in the NPRM. For all head restraints, gaps within the restraint are limited to not more than 60 mm.

Under today's rule, an adjustment retention mechanism that locks into place is mandatory for all adjustable head restraints. NHTSA will test retention of the head restraint in its vertical position 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 will be 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 will be conducted using a linear impactor, rather than the proposed free-motion impactor or the pendulum impactor used in ECE 17.

The dynamic compliance option will utilize 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 HIC

is 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.

Between the effective date of today's rule and September 1, 2008, manufacturers may 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 we are permitting compliance with ECE 17 during the interim.

The ECE has two regulations applicable to head restraints, ECE 17 and ECE 25.

The two regulations have similar requirements. However, the provisions of ECE 17 supersede the requirements of ECE 25 for most vehicles subject to this final rule. Specifically, as amended in July 2002, ECE 17 applies to vehicles in the following categories:

ECE 25, Uniform Provisions Concerning the Approval of Head Restraints (Head Rests), whether or not Incorporated in Vehicle Seats (

http://www.unece.org/trans/main/wp29/wp29regs/r025r1e.pdf

1. Passenger vehicles, including multipurpose passenger vehicles (MPVs) with 9 or fewer designated seating positions (“M1”).

2. Passenger vehicles, MPVs and buses with more than 9, but less than 17 designated seating positions (“M2” and “M3”).

We note that buses with at least 17 designated seating positions are still classified as M2, M3. However, ECE 17 specifically excludes these vehicles.

3. Trucks (“N”).

This final rule applies to passenger cars, MPVs, trucks and buses with a GVWR of 4,536 kg or less. Accordingly, the only vehicles that will be subject to this final rule, but will not fall under the requirements of ECE 17, are buses with at least seventeen designated seating positions. Because of the GVWR limit, it is unlikely that such buses will be subject to this final rule. Nevertheless, we note that the requirements of ECE 25 are more stringent than those of this final rule because they mandate rear head restraints. Since we want to provide a compliance option for the interim period that is functionally equivalent to the current standard, we decided that all vehicles, including large capacity buses subject to this final rule, may certify to the specified ECE 17 requirements instead of ECE 25.

We note that ECE 17, Paragraph 5.3.1 expressly allows other categories of vehicles equipped with head restraints to be certified to ECE 17.

During this interim period, manufacturers must irrevocably elect one of the compliance options in its entirety and may not certify under an alternative compliance option, if there is a noncompliance. This restriction is necessary because each certification option addresses the risks associated

with poor head restraint design differently, and because individual parts of each of the compliance options provide different levels of safety. We note, however, that the manufacturer may select different compliance options for different designated seating positions.

Major differences between this final rule and the NPRM.

The following highlights the major differences between the NPRM and the final rule:

• This final rule does not require head restraints in rear outboard designated seating positions. However, if a manufacturer chooses to install head restraints in rear outboard seating positions (as defined in FMVSS No. 202a.), these head restraints must meet the new height, strength, position retention, and energy absorption requirements, but not backset requirements.

• The maximum allowable backset for front head restraints has been increased from 50 mm to 55 mm;

• The 25 mm gap limit for adjustable head restraints in their lowest height position and a single position of backset adjustment has been eliminated, leaving the 60 mm limit at any position of backset adjustment;

• With respect to position retention, the head restraint must return to within 13 mm of the initial reference point, instead of to within 10 mm, as proposed;

• The proposed radius of curvature requirement has not been adopted;

• The energy absorption testing procedure will be conducted using a linear impactor, instead of the proposed free-motion impactor;

• The dynamic compliance option will require that the head-to-torso rotation be limited to 12 degrees, when tested with a 50th percentile male Hybrid III dummy with the head restraint midway between the lowest and the highest position of adjustment (there will be no test with a 95th percentile dummy);

• The dynamic compliance option mandates a maximum HIC

limit of 500, as opposed to 150 proposed in the NPRM, and;

• Vehicle owner's manual must include information describing the vehicle's head restraint system, how to properly adjust head restraints, and how to remove and re-install head restraints.

VI. Height and Width Requirements

a. Requirements for Front Seats

Height of front seat head restraints.

FMVSS No. 202 currently requires that front head restraints be capable of reaching a height of at least 700 mm above the SgRP. The NPRM proposed amending the standard to increase the minimum height of front integral head restraints to 800 mm above the H-point. It proposed that if the head restraints were adjustable, they must adjust up to at least 800 mm, and not below 750 mm, with respect to the H-point. This adjustment range was estimated to ensure that the top of the head restraint exceeded the head C.G. (center of gravity) for an estimated 93 percent of all adults.

A majority of the manufacturers and other commenters, among them the Alliance of Automobile Manufacturers (Alliance), General Motors North America (GM), TRW Automotive (TRW), the Association of International Automobile Manufacturers, Inc. (AIAM) and IIHS, generally supported the new height proposal. IIHS's support was based, in part, on a new standard for evaluating head restraints promulgated by the Research Council for Automobile Repairs (RCAR), which deems taller head restraints to be superior to shorter ones.

In contrast, Advocates commented that fixed and adjustable head restraints should be subject to the same height requirements. According to Advocates, the NPRM did not justify allowing a 750 mm height for adjustable restraints in front seats.

RCAR is an international organization intended to reduce insurance costs by improving automotive damageability, repairability, safety and security (

www.RCAR.org

). Under the RCAR standards, the head restraint is tested with the HRMD to evaluate the restraint geometry and then is rated as good, acceptable, marginal, or poor. These types of rating systems do not contain the level of objectivity or specificity to translate easily into a regulatory requirement.

There were some concerns expressed about the effect of taller front outboard head restraints on driver visibility through the backlight,

and on the ability of drivers in following vehicles to see through the backlight of a vehicle in front of them. Honda and Ford also said that taller front seats would contribute to rear seat occupants feeling closed-in.

Backlight is the window located at the rear of the roof panel (SAE J953).

Several manufacturers also stated that the taller head restraints could make it more difficult to install seats during vehicle assembly.

Agency response:

The persistence of high numbers of whiplash injuries in the current fleet of vehicles indicates that the height requirement currently in effect for front outboard head restraints is not preventing excessive movement of the head and neck relative to the torso. The current requirement allows head restraints that do not effectively limit rearward movement of an average occupant's head at its center of gravity, resulting in continuing high numbers of whiplash. Research indicates that a minimum height of 800 mm above the H-point for integral head restraints, and a minimum height of 750 mm for adjustable head restraints in their full down position and at least 800 mm in their full upward position, will prevent whiplash injuries because at this height the head restraints can effectively limit the movement of the head and neck.

We have decided against adopting Advocates' suggestion that adjustable head restraints should not be allowed to have an adjustment position below the minimum 800 mm requirement set for integral head restraints.

Advocates' argument was based on the possibility that occupants will not adjust their head restraints to an effective position. We acknowledge that head restraint misuse has been a problem in the past and that some consumers may not receive the full benefit of an adjustable head restraint if they leave them in the lowest possible position of adjustment. However, we believe that misuse will decrease as consumers become more aware of the merit of raising their head restraints.

We note that heights greater than 800 mm are permitted for both integral and adjustable head restraints.

Further, prohibiting any position less than 800 mm for adjustable head restraints would likely result in a substantial increase in the overall height of the seat back. (The gap between the top of the seat back and the head restraint in its lowest position could not be widened substantially, because of the restrictions in today's rule that restricts such gaps to 60 mm.) The practical effect of adopting Advocates' suggestion would be to require integral head restraints, which we believe is unwarranted and overly design restrictive. Adjustable head restraints may allow shorter and very tall occupants to position their head restraints more optimally. Further, even occupants of average size may benefit from certain adjustment features, such as head restraint backset adjustment to positions closer than 55 mm, if they find it comfortable. Finally, when properly designed to maintain their position, adjustable head restraints can provide protection comparable to that provided by integral head restraints.

We note that integral head restraints have in the past been considered more effective than adjustable head restraints, largely because many occupants do not properly position adjustable head restraints. In 1982, NHTSA assessed the performance of head restraints installed

pursuant to FMVSS No. 202 and reported that integral head restraints are 17 percent effective at reducing neck injuries in rear impacts and adjustable head restraints are 10 percent effective at doing so. The difference was due to integral head restraints' being higher with respect to the occupant's head than adjustable head restraints, which were normally left down. More recently, however, the Preliminary Economic Assessment (PEA) for the NPRM found no statistical difference in the protection offered by adjustable and integral head restraints. This may be attributable to increases in the height of adjustable head restraints relative to integral head restraints since the 1982 NHTSA study.

With respect to comments on visibility concerns, we do not believe that the greater height of front seat head restraints will decrease rearward visibility. Numerous vehicles currently produced for the U.S. market already have head restraints reaching 800 mm without reports of visibility problems. In its comment, Transport Canada referred to a study conducted by Biokinetics & Associates entitled, “The Effects of Increased Head Restraint Height on Driver Visibility,” in support of its suggestion that increasing the height of head restraints would not result in any major visual obstruction. The study indicated that a fixed head restraint tall enough to accommodate a 95th percentile male would have a negligible effect on driver visibility in 83 percent of vehicles in the fleet, as compared to an adjustable head restraint in the lowest position.

With regard to concerns about the difficulty of manufacturing vehicles with taller head restraints, we do not believe this is a major manufacturing obstacle. Numerous manufacturers already comply with ECE17, which requires front head restraints to be as tall as in this rule.

Further, the manufacturers will have ample opportunity to address vehicle assembly processes during the interim period before the final rule becomes effective.

We also note that some vehicles already feature rear seat head restraints that would comply with the new height, backset, strength, position retention, and energy absorption requirements for optional rear outboard head restraints.

Some commenters believed that taller front seat head restraints will make rear seat passengers feel “closed in” and claustrophobic. There has been no indication of such problems from the European markets where rear seat passengers are already subjected to taller head restraints in the front outboard seating positions. We are unable to conclude, without supporting data, that a head restraint that is less than 100 mm (4 inches) higher than current restraints is generally likely to have this effect on passengers.

Nissan and ICBC requested that height and backset requirements, as applied to active or dynamically deployed head restraints, be measured when such head restraints are fully activated. Unless the system is tested when fully activated, Nissan claimed that the active head restraint system currently featured in several Nissan and Infiniti vehicles would not pass under the new static testing requirements.

We believe that it may be difficult to deploy these systems manually and to keep them deployed while making static measurements, unless the actual seat is partially disassembled. Further, this artificially deployed position may not accurately represent position of the head restraint when the occupant's head comes in contact with it during a rear impact. The agency knows of no practicable way to address these issues in the context of a static test nor did any commenter present one. Accordingly, this rule requires that front outboard active head restraint systems be tested for height in their un-deployed position. We note that there are practical limitations of any static test procedure on a system with dynamic properties.

However, if an active head restraint were to meet the static test procedure requirements, this would not eliminate the value of the active nature of those head restraints since further gains in controlling the occupant's head-to-torso motion and energy absorption could be achieved.

We note that the manufacturers' concerns are alleviated by the availability of the dynamic compliance option. The dynamic compliance option provides an alternative for those manufacturers who are now utilizing active or dynamic head restraint systems. Agency testing and other published research have shown that an active head restraint system can be designed to meet dynamic testing requirements with a comfortable compliance margin. Further, a manufacturer electing to certify compliance via dynamic testing is relieved from multiple static performance requirements. Our analysis also indicates that several active head restraint systems currently on the market would pass our static compliance requirements in their normal or non-deployed position. Accordingly, we believe most head restraints will be able to meet today's static test requirements. For those that cannot, the dynamic compliance option remains available.

Front head restraints in low roofline vehicles.

This rule permits a lower minimum height for head restraints for front outboard-designated seating positions to allow a maximum of 25 mm of vertical clear space between the top of the front head restraint and the roofline. The NPRM proposed to permit a similar exception during the interim period as part of the option of complying with ECE 17. ECE 17, paragraph 5.5.4 allows for up to 25 mm of clear space between front head restraint and any fixed vehicle structure, provided that use of the exception does not result in a height lower than 700 mm.

For front head restraints, DaimlerChrysler, Nissan, Alliance, Volkswagen, and Porsche requested that the 25 mm clearance exemption remain in the final rule to accommodate the possible situation in which the 800 mm head restraint may not clear the roof or front header when the seat back is folded for egress to or ingress from the rear seat area. In response to these comments we decided to adopt a 25 mm height allowance in this final rule. As in ECE 17, paragraph 5.5.4, the 25 mm height allowance is limited to the extent that the resulting front head restraint height cannot fall below 700 mm. However, this rule permits the 25 mm height allowance only in situations in which a full height front head restraint would interfere with the roofline, but not with any fixed vehicle structure, as allowed by ECE. We believe adopting the full ECE exception could provide relief in instances in which none may be needed. For example, an upper seat belt anchorage or the side of the vehicle's interior could be within 25 mm of the head restraint and yet would likely not create any compliance difficulties for vehicle manufacturers or unduly restrict visibility.

The 25 mm height allowance for rear head restraints is described in the next section.

Width of front seat head restraints:

The NPRM proposed to maintain the existing width requirements of FMVSS No. 202:

i.e.

, that both front and rear outboard seat head restraints must be at least 171 mm (6.7 in) wide on single seats and 254 mm (10 in) wide on bench seats.

We note that ECE 17 regulation provides a 170 mm minimum width requirement for all head restraints. In the NPRM, we stated that bench seat head restraints should be wider because occupants seated on bench seats are freer than occupants of single seats to position themselves so that they are not directly in front of the head restraint.

A bench seat is a seat that has a center designated seating position between the two outboard designated seating positions.

AIAM called the proposed 254 mm head restraint width for bench seats unreasonable, stating that NHTSA should instead adopt the same 170 mm width for bench seat head restraints. AIAM asserted that comfort factors and seat belt placement on most bench seats help place occupants in the proper seating positions. In contrast, Advocates

expressed concern that requiring a 254 mm width for bench head restraints and a 170 mm width for non-bench head restraints would protect only target occupants in centered, perpendicular rear impacts, not occupants in offset collisions, causing head/neck excursion to one side of the restraint. Given those concerns, Advocates stated it did not understand why all restraints, especially front head restraints, should not have a minimum width of 254 mm.

For front bench seats we disagree with AIAM that the width requirement should be reduced. The 254 mm width requirement for these head restraints on bench seats has been in effect since January 1, 1969. We are not aware of any evidence showing that the present level of protection should be reduced. We decided to maintain wider head restraints for front bench-type seats because wider head restraints tend to better reduce relative head-to-torso motion in off-axis impacts. However, rather than use the term “bench,” which some commenters felt required further clarification, we have defined the requirement in terms of front outboard designated seating positions in vehicles that have a front center designated seating position.

With regard to Advocates' comment, NHTSA declines to require all head restraints to have a minimum width of 254 mm. With respect to front outboard seating positions, we note that front outboard non-bench seats have a defined contour that, in addition to belt use, better prescribe occupant seating position relative to the head restraint. Therefore, the front non-bench head restraints can be narrower than the front bench seat head restraints. With respect to rear outboard seating positions, we believe that the rearward visibility concerns associated with wider rear head restraints outweigh an unquantified off-axis rear impact benefit of wider restraints in all seats at this time.

b. Requirements for Rear Seats Equipped With Head Restraints

In the NPRM, we proposed to require head restraints in rear outboard seating positions. Presently, neither FMVSS No. 202 nor ECE 17 requires head restraints in rear outboard seating positions. Based on further analysis of the proposal and submitted comments, we have decided not to require head restraints in rear outboard designated seating positions. For a more detailed discussion of our decision not to require head restraints, please see section XII.

While rear head restraints are not required, this final rule does impose certain requirements on head restraints voluntarily installed in outboard designated seating positions. The strength, position retention, and energy absorption requirements are the same for front outboard and optional rear head restraints. However, the requirements for height and width differ from those applicable to front outboard head restraints.

Height of rear seat head restraints.

The NPRM proposed that rear restraints have a minimum height of 750 mm if integral and, if adjustable, not be adjustable to a height below 750 mm.

DaimlerChrysler, GM, Honda, and the Alliance expressed concern about diminished visibility and decreased functionality of rear seat storage due to the taller rear seat head restraints. As a result of this expected decline in visibility and utility, DaimlerChrysler indicated that customer dissatisfaction with the restraints could trigger misuse or removal. Johnson Controls expressed concerns pertaining to reduced rearward visibility (particularly for shorter drivers), as well as feasibility issues, including difficult ingress/egress for third-row SUV or van seating, inability to fold and install all rows of seats, and lack of clearance between head restraints and the rear backlight area for sport coupes with rear seating.

Porsche objected to the 750 mm rear head restraint height, claiming impracticability and lack of safety need. Porsche indicated that some of its current fleet would be unable to meet the new height requirements for rear head restraints. Specifically, Porsche presented their computer aided design data showing that several models, including the 911, have less than 750 mm of distance between the rear seat H-point and the roofline, making compliance with the proposed requirements impossible.

Accordingly, Porsche asked that the final rule either not require rear head restraints, or provide an exception for low roofline vehicles. Magna and Volkswagen also requested that a 25 mm clearance between the top of head restraint and the roofline be allowed regardless of the actual head restraint height measurement. Such a provision would be similar to an ECE 17, Paragraph 5.5.4, which allows head restraints to have a lower maximum height in order to provide 25 mm of clear space between the head restraint and the roofline. Nissan suggested allowing a 25 mm clearance between the head restraint and interior vehicle structures as necessitated by vehicle design.

The distance from the H-point to the point 25 mm below the roofline for 911 Coupe, Targa, and Cabrio models is 693, 666, and 691 mm, respectively. Porsche also noted that requiring rear head restraints in such vehicles would create an almost 100 percent rear window obstruction (Docket No. NHTSA-2000-8570-39).

In contrast, Advocates argued for an 800 mm minimum height for rear seat head restraints, in order to include (according to the commenter) sufficient whiplash protection for 95th percentile male adults.

Agency response:

As discussed above, NHTSA has concluded that any voluntarily installed rear head restraints must meet the height requirements proposed in the NPRM. Specifically, the optional rear head restraints must reach a minimum height of not less than 750 mm above the H-point.

In the NPRM, we indicated that the 750 mm minimum head restraint height would reach above the head center of gravity of approximately 93 percent of all adults. We note that with respect to the rear seat head restraint target population, the 750 mm height would sufficiently protect an even higher percentage of rear seat passengers because larger occupants typically sit in front seats.

Some manufacturers stated that a taller rear head restraint might interfere with seat mechanisms designed to provide access to and from third row seats. Because we have decided not to require rear head restraints, a manufacturer concerned with functionality of these mechanisms need not install a head restraint in the affected seats. Additionally, as will be discussed in sections IX.b. and c., the manufacturers will be allowed to install removable rear outboard head restraints or rear outboard head restraints with “non-use positions.”

Several commenters discussed the possible effects of the proposed head restraint height increases on vehicle utility with respect to seat folding and cargo capacity. The Alliance, DaimlerChrysler, Honda and GM commented that the rear head restraint heights proposed in the NPRM could impede seat folding, thus limiting cargo capacity, or otherwise limit interior configuration possibilities.

Since rear outboard head restraints will not be mandatory, vehicle manufacturers need not equip their rear seats with head restraints. Further, as will be discussed in section IX, if the manufacturers provide rear outboard head restraints, they will be allowed to make them removable and to design them so that they can be moved into “non-use positions.” As a result, manufacturers will have ample design flexibility to address the cargo carrying needs of their customers.

Rear head restraints in low roofline vehicles.

This rule permits a lower minimum height for rear outboard seating positions equipped with optional head restraints to allow a maximum of 25 mm of vertical clear space between the top of the rear head restraint and the roofline or the backlight. The NPRM proposed to permit a similar exception during the interim period as part of the option of complying with ECE 17. ECE 17, paragraph 5.5.4 allows for up to 25 mm of clear space between rear head restraint and any fixed vehicle structure, provided that use of the exception does not result in a height lower than 700 mm.

We decided to adopt a similar provision for the long term. However, this rule permits the 25 mm height allowance only in situations in which the rear head restraint interferes with the roofline or the rear window, but not with any fixed vehicle structure as allowed by ECE. Further, the 25 mm height allowance is permitted only if the interference occurs when seats are positioned as intended for occupant use.

The term “intended for occupant use” has been defined in the final rule to apply to seat positions other than those intended solely for the purpose of allowing ease of ingress and egress of occupants and access to cargo storage areas of a vehicle.

In their comments, DaimlerChrysler, Nissan, Alliance, Volkswagen, and Porsche asked for a permanent 25 mm height allowance and suggested that the clearance should apply in situations where the seat interferes with all fixed vehicle structures, including roof liners, seat backs, headers, and rear windows. Further, they stated the clearance should be allowed regardless of whether the seats are placed in either upright or folded down positions.

This final rule does not permit a 25 mm height allowance in situations in which the rear head restraint interferes with fixed vehicle structures other than the roofline or the backlight. We believe adopting the full ECE exception could provide relief in instances in which remedies other than changing the basic vehicle structure are available.

As previously stated, the rear seat 25 mm height allowance in this final rule applies only to seat adjustment positions intended for occupant use.

That is, if a second row seat folds forward to permit ingress and egress and would hit the seat in front of it or some other vehicle structure, the 25 mm height allowance is not available for that situation. In situations in which interference occurs when a seat is not in a position intended for occupant use, the manufacturers may choose to utilize the “non-use” head restraint positions described later in this document, or redesign the seat fold-down mechanisms. We note that redesigning the fold down mechanism, though not necessitated by this final rule, can provide a practicable resolution at a reasonable cost.

We note that both front and rear optional head restraints must meet the applicable height requirements with the seat positioned as intended for occupant use.

The ECE 25 mm height allowance is limited to the extent that the resulting head restraint height cannot fall below 700 mm. As a practical matter, however, this requirement is moot with respect to the upgraded standard because the rear seat backs and attached or adjacent components that have a height of less than 700 mm are not considered rear head restraints under this final rule.

Width requirements for rear head restraints.

The agency tentatively concluded in the NPRM that a 171 mm width for single seats and a 254 mm width for bench seats were the appropriate specifications for all outboard seating positions. These proposed widths differed from ECE 17, Paragraph 5.10, which provides a 170 mm minimum width requirement for all head restraints. The NPRM asked whether NHTSA should implement specific requirements for rear seat head restraints in order to alleviate problems associated with potential visibility losses.

All industry commenters agreed that the appropriate width requirement for rear seat head restraints should be 170 mm, and that 254 mm is overly wide. Honda commented that the 254 mm bench seat width requirement could reduce rearward visibility and was unwarranted, given the unknown safety problems of rearward visibility reduction and the unidentified need for wider head restraints. Honda attached the results of a simulation it conducted to show the decreased visibility created when 750 mm high, 254 mm wide head restraints are installed in a coupe and a hatchback vehicle. When 254 mm wide head restraints were installed on a second row rear bench seat of a coupe model, Honda's simulation showed a 40 percent decline in rearward visibility. Similarly, when installed on a hatchback model, the 254 mm wide head restraints produced a 60 percent loss of rearward visibility. To rectify this reduction of rearward visibility, Honda suggested a head restraint minimum width requirement of 170 mm for both bench seats and individual seats. Honda based this 170 mm requirement for both types of seats on ECE 25.

Ford presented data from a study it conducted, showing that rear head restraints with widths of 171 mm trimmed backlight visibility by 10-12 percent, while 254 mm wide rear head restraints reduced visibility by 15-17 percent.

In contrast, Advocates stated that it believed that all restraints should have a minimum width of 254 mm.

Upon reviewing the comments, NHTSA has decided to require a 170 mm minimum width for all voluntarily installed rear head restraints. This decision was made to further reduce the effects of this rule on rearward visibility. In order to harmonize our requirements with that of ECE 17, we are adopting a 170 mm minimum width, as opposed to the 171 mm proposed in the NPRM.

VII. Backset Requirements for Front Seats

In the NPRM, we proposed that the front and rear outboard head restraints have a backset of no more than 50 mm, as measured by HRMD. “Backset” means the minimum horizontal distance between the back of a representation of the head of a seated 50th percentile male occupant and the head restraint (

i.e.,

the back of the ICBC head form and the head restraint). The 50 mm maximum backset requirement was to be met at all head restraint heights between 750 mm and 800 mm. We solicited comments on whether a maximum 50 mm backset limit would be effective in preventing whiplash injuries; whether 50 mm backset would provide sufficient comfort for the occupants; and whether an adjustable backset would be more appropriate.

Commenters offered a range of opinions about the need for, and acceptable level of, a maximum backset requirement. Several commenters, including ICBC, IIHS, Transport Canada, and Advocates, supported establishing 50 mm as the maximum allowable backset. ICBC and Magna Seating Systems argued that Mathematical Dynamic Model (MADYMO) simulations performed by NHTSA confirm the decreasing safety benefit of head restraints with backsets greater than 50 mm. Therefore, ICBC believes 50 mm is sufficient to reduce whiplash significantly.

ICBC provided data showing 49 of 164 vehicles manufactured in 2001 by 19 different manufacturers have a backset of 50 mm or less.

IIHS stated that a group of model year (MY) 2001 vehicles,

among them Jeep Cherokee, Ford Ranger, Toyota Camry, and Volvo S80 already have 50 mm or smaller backsets. Because many newer vehicles already have backsets of 50 mm, these commenters claimed it was evident that the 50 mm requirement provides sufficient head clearance and that passenger comfort would not be compromised in a significant manner. IIHS stated that it was unaware of any significant comfort issues.

We note that the ICBC evaluated backset using the measurement technique and seat back angle identical to that of this final rule.

In opposition, a majority of the manufacturers, among them GM, Magna, Johnson Controls, AIAM, the Alliance, Nissan, Porsche, DaimlerChrysler, and Ford, suggested that vehicle occupants would prefer a head restraint backset of more than 50 mm. Specifically, they maintained that smaller female occupants tend to utilize steeper seat back angles. According to these commenters, a backset of 50 mm may cause significant intrusions into the space where these occupants typically place their heads, forcing their heads into an unnatural forward-tilting position. DaimlerChrysler indicated that a recent decrease in the backset to 50 mm in one of its models yielded four times as many warranty claims for the new head restraint. It did not elaborate on the basis for these claims. Autoliv commented that even a 50 mm backset is not a guarantee to prevent whiplash, and that it will lead to discomfort for more than 20 percent of the occupants. General Motors and Ford suggested that an 80 mm backset is more appropriate to accommodate consumer comfort.

Some commenters stated that IIHS rates backsets of 70 to 90 mm “acceptable” and so that backset requirement should be increased to that range.

The University of Michigan Transportation Research Institute (UMTRI) commented that it had conducted an extensive study of vehicle occupants' posture and position. Based on its research, a 50 mm backset would result in head restraint interference for 13 percent of the driving public.

The head restraint would actually come in contact with the hair of approximately 33 percent of drivers, assuming a hair margin of 25 mm. Based on their calculations, the individuals who preferred seat back angles more upright than 25 degrees (usually small stature people) were most likely to be subject to the head restraint interference. UMTRI estimated that with current seat designs, a backset of 91 mm would accommodate the preferred head positions of 99 percent of the population and a 70 mm maximum backset would accommodate all but a small percentage of the population.

The UMTRI evaluated backset of 50 mm at the seat back angle of 25 degrees, using a CAD representation of a HRMD and a typical seat.

Ford cited 3 studies by Eichberger

et al.,

Szabo

et al.,

and Davidsson

et al.,

which used sled-mounted seats to simulate low speed rear impacts. Eichberger

et al.

tested volunteers on 9 different seat types at simulated impact speed changes (delta Vs) of 8 and 11 km/h. When the measured backset was less than 70 mm, none of the volunteers complained of any discomfort or pain. Szabo

et al.

tested 5 volunteers at delta Vs of 8-10 km/h under two conditions: an unmodified head restraint, and the same head restraint with 50 mm of additional padding. Backsets for the volunteers ranged between 76 to 114 mm with the unmodified head restraint, and by assumption between 26 to 64 mm with the modified head restraints. None of the volunteers reported any discomfort or pain after either test. Davidsson

et al.

subjected 13 volunteers to multiple sled tests (2-4) with delta Vs of 5 to 7 km/h. The measured backsets ranged from 70 to 160 mm. The head restraint position was not varied during the test so the variation in backset for the different occupants was due to occupant size differences. Only one subject reported any symptoms. The symptom was a headache, which occurred after his third run, and desisted within 36 hours.

Eichberger A, Geigl BC, Moser A, Fachbach B, Steffan H, Hell W, Langwieder K; Comparison of Different Car Seats Regarding Head-Neck Kinematics of Volunteers During Rear End Impact; Proceedings of the 1996 International IROCBI Conference on the Biomechanics of Impact; September 1996; pp. 153-164.

Szabo TJ, Welcher JB; Human Subject Kinematics and Electromyographic Activity during Low Speed Rear Impacts, Proceedings of the 40th Stapp Car Crash Conference; November 1996, 962432, pp. 235-315.

Davidsson J, Deutscher C, Hell W, Linder A, Lovsund P, Svensson: Proceedings of the 1998 International IRCOBI Conference of the Biomechanics of Impact: September 1998; pp. 289-301.

We also received a comment from Cervigard, Inc., which has designed a head restraint that incorporates a contoured shape intended to match the curvature of the head and cervical spine, which is essentially a neck bolster. In Appendix B of this NPRM, we discuss our reasons for not adopting a requirement for a neck bolster.

Agency response:

This final rule requires that front outboard head restraints meet the backset requirements described below. Because of occupant comfort countermeasure issues unique to rear seats, the agency decided not to regulate backset in the rear designated seating positions voluntarily equipped with head restraints. We concluded that comfort-related issues are not insurmountable in front seats because front seat backs can be adjusted to alleviate discomfort. Further, as explained further below, our Final Regulatory Impact Analysis (FRIA) does not attribute any safety benefits to vehicle occupants as a result of regulating backset in rear seats.

For front outboard designated seating positions, we have decided to increase the maximum allowable backset to 55 mm, with the seat back positioned at an angle that gives the HRMD a torso reference line angle of 25 degrees. Our decision to relax the maximum allowable backset requirement is based on the ± 5 mm tolerance of the measuring device. This tolerance is discussed more fully in the next section. Briefly stated, a 5 mm increase beyond the 50 mm limit proposed in the NPRM represents the variability associated with measuring backset with the ICBC measuring device.

In sum, under today's rule, the backset for front outboard head restraints must not be adjustable beyond the new maximum allowable distance of 55 mm when the head restraint is at a height between 750 mm and 800 mm, inclusive. Backset adjustment to distances below 55 mm is allowed. Also, backset adjustment of above 55 mm at head restraint positions higher than 800 mm is allowed. For manufacturers of active head restraint systems who choose to certify to the static dimension and strength requirements, the backset measurements will be taken with the head restraints in non-deployed position because we believe that the artificially deployed position may not accurately represent the actual position of the head restraint when the occupant's head comes in contact with it.

Necessity for a limited backset.

Our decision to propose a 50 mm backset was based on published research, testing, computer modeling, and real world crash data.

The consensus within the biomechanics community is that the backset dimension has an important influence on forces applied to the neck and the length of time a person is disabled by an injury. As early as 1967, Mertz and Patrick first showed that reducing the initial separation between the head restraint and head minimizes loading on the head during a rear impact.

More recently, the Olsson

study, which examined neck injuries in rear end collisions and the correlation between the severity of injuries and vehicle parameters, showed that the duration of neck symptoms was correlated to the head restraint backset. Specifically, reduced backset, coupled with greater head restraint height, results in lower injury severity and shorter duration of symptoms.

Mertz, H.J.; Patrick, L.M.: “Investigation of the Kinematics and Kinetics of Whiplash,” Proceedings of the 11th Stapp Car Crash Conference, Anaheim, California, 1967; pp. 267-317.

Olsson, I., Bunketorp, O., Carlsson G., Gustafsson, C., Planath, I., Norin, H., Ysander, L. An In-Depth Study of Neck Injuries in Rear End Collisions, 1990 International Conference on the Biomechanics of Impacts, September, 1990, Lyon, France. See Table IV and the Appendix.

A different study examined sled tests to determine the influence of seat back and head restraint properties on head-neck motion in rear impacts. The study concluded that the head restraint backset had the largest influence on the head-neck motion among all the seat properties examined. With a smaller backset, the rearward head motion was stopped earlier by the head restraint, resulting in a smaller head to torso displacement. The findings indicated that a reduction in backset from 100 mm to 40 mm would result in a significant reduction in whiplash injury risk.

Svensson, M., Lovsund, P., Haland, Y., Larsson, S. The Influence of Seat-Back and Head-Restraint Properties on the Head-Neck Motion During Rear-Impact, 1993 International Conference on the Biomechanics of Impacts, September, 1993, Eindhoven, Netherlands.

A study conducted by Eichberger examined real world rear crashes and sled tests with human volunteers to determine whiplash injury risk and vehicle design parameters that influence this risk. The study found a positive correlation between head restraint backset and head to torso rotation of the volunteers and to the reported whiplash injury complaints. The most important design parameters were a low horizontal distance between the head and head restraint as well as the head restraint height.

Eichberger A, Geigl BC, Moser A, Fachbach B, Steffan H, Hell W, Langwieder K. Comparison of Different Car Seats Regarding Head-Neck Kinematics of Volunteers During Rear End Impact, International IRCOBI Conference on the Biomechanics of Impact, September, 1996, Dublin.

A study conducted by Dr. Allan Tencer, PhD, used rigid occupant body models enhanced with finite element models of the cervical spine for simulating rear impacts in order to examine the effect of backset on neck kinematics and forces and moments in the neck. The study concluded larger backset correlates to greater displacement between cervical vertebrae and shearing at the facet capsules that are likely associated with whiplash injury. With the head initially closer to the head restraint, the time difference between the occurrences of the peak upper and lower neck shear forces are smaller. At 50 mm backset and lower, the head moved more in phase with the torso and extension of the head was reduced indicating a lower risk of whiplash injury.

IIHS, in its studies of head restraints, considers a backset of 70 mm (2.8 inches) or less to be “good.”

Tencer, A., Mirza, S., Bensel, K. Internal Loads in the Cervical Spine During Motor Vehicle Rear-End Impacts, SPINE, Vol. 27, No. 1 pp 34-42, 2002.

The IIHS head restraint rating criteria is discussed at:

http://www.iihs.org/vehicle_ratings/head_restraints/head.htm.

NHTSA used computer modeling described in the NPRM to verify our assumption regarding the benefits of a smaller backset. Our research indicates that lower head-to-torso rotation values were seen when the backset was approximately 50 mm in comparison to head restraints with large backset values. As discussed further in this notice, lower head-to-torso rotation values are predicted to result in a lower probability of whiplash injury. Therefore, we continue to conclude that 50 mm of backset is an appropriate upper limit for all outboard seating positions. No data presented in the comments have indicated that a higher backset value is more appropriate from the occupant safety-standpoint. Other than Ford's comments, all of the comments opposing the proposed 50 mm maximum backset were related to comfort issues and the repeatability of placement of the proposed test device. In sum, research indicates that limiting backset is critical to reducing whiplash injuries occurring in rear impacts.

In its comments, Ford referred to three crash studies conducted at delta V's ranging from 5 to 11 km/h with varying degrees of backset and occupant size. Ford emphasized that there were no occupant injuries both with and without the backset reduction. We note that all of these tests utilized volunteers and therefore, the impact delta Vs were intended to be below the injury threshold. The primary goal of these studies was to understand occupant kinematics. The same research also indicated that when backset was reduced from 76 mm to 26 mm and from 114 mm to 64 mm, the head acceleration, rearward head displacement and cervical extension were all reduced. These data confirm our contention that injury measures, including head-to-torso rotation, decrease with smaller backset and predict a lower probability of injury. While some of the data supplied by Ford seems to suggest that smaller backsets have no bearing on the occurrence of whiplash injuries at low speeds, we note that if all impacts in the real world were limited to this very slow speed, the backset limit indeed might not be as critical. The same data seem to support our rulemaking efforts, as Eichberger observed that backset “is very important for a good seat design. Even a head restraint placed high enough can only prevent neck injuries when the head is sustained as soon as possible by the head restraint during rear end collision.”

See

Eichberger at pp. 153-164.

Finally, we note that other seat parameters beyond the head restraint geometry play a role in risk of injury in rear impacts. Specifically, seat back frame force deflection characteristics and seat upholstery compliance characteristics can influence the occupant's kinematics. Thus, the head restraint geometric requirements specified in this final rule should be thought of as an interim step in the agency's goal of a unified seat/head restraint standard.

Comfort of the seat occupant.

In selecting a backset limit, we have attempted to balance comfort, safety and measurement variability concerns. As noted above, 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. Numerous commenters, however, stated that occupants may be intolerant of head restraints very close to the back of their head. Further, because of differences in the occupant size, posture and seat angle preference, the same head restraint can yield different amounts of backset clearance for different individuals.

Several manufacturers argued that some occupants would select a steeper or more upright front seat back angle, thus causing the backset distance to be below 50 mm. They contend that a backset of less than 50 mm will interfere with the normal position of the head. However, since ICBC reported that 49 of 164 vehicles from model year 2001 met the 50 mm backset limit, it appears that occupant discomfort in front seats is not an insurmountable obstacle. Accordingly, we conclude that the available information does not substantiate the industry concerns associated with discomfort from front seat back adjustment to a more upright position.

UMTRI commented that a 50 mm backset causes interference with 13 percent of drivers “preferred” head position. Generally, these tend to be smaller occupants, who prefer a more

upright seat back angle. The “preferred” backset position, as articulated by UMTRI, may merely refer to a position that the drivers are most accustomed to. The term does not necessarily mean that the position is the only acceptable one or even the safest one for a given occupant. We note that the driving population as a whole is accustomed to a backset position that is, while comfortable, not optimal to prevent whiplash injuries.

We believe that no significant deviation from our proposed backset limit of 50 mm is necessary to provide an overwhelming majority of front seat occupants with an acceptable backset position. Further, any potential discomfort can be reduced by a slight increase in seat back angle. We believe that most front seat occupants can increase the seat back angle slightly without compromising their ability to reach the steering wheel comfortably or see the road ahead. For every additional degree of inclination, approximately 3 mm of additional backset clearance would be obtained. For example, a 2-degree increase in seat back angle will result in additional 6 mm of backset.

In addition to potential ways to alleviate potential discomfort, we note that our own measurements of 14 vehicles showed that the front seat head restraints in the MY 1999 Toyota Camry, Chevy C1500, Chevy S10, Saab 9-5, and Chevy Malibu, all had backsets within the proposed 50 mm limit. This supports comments by ICBC and IIHS that many vehicles already have a 50 mm backset. We think the seat manufacturers can provide a front seating system design, such as a different head restraint shape, that would allow for better comfort.

With respect to rear seats, however, the agency believes that potential occupant discomfort cannot be as easily reduced because most rear seat backs in passenger cars are not adjustable. In many vehicles, the rear seat back angle cannot be changed to provide additional backset clearance. Consequently, some vehicle occupants may experience interference with the normal position of their head, and could decide to completely remove the optional rear head restraints. NHTSA believes that it is preferable that the rear head restraints remain in the vehicle instead of being removed due to occupant discomfort, because we estimate that the increased height of optional rear head restraints will result in 1559 fewer whiplash injuries each year. Further, we are concerned that some manufacturers may choose not to install optional rear head restraints due to concerns of customer dissatisfaction with uncomfortable rear head restraints.

Because of rear seat occupant comfort concerns, the agency decided not to limit the amount of backset in the rear designated seating positions equipped with optional head restraints.

Because of abundant scientific evidence showing that smaller backset reduces instances of whiplash injuries, we believe that the vehicle manufacturers will install optional rear head restraints in a manner that will strike a proper balance between rear seat occupant safety and comfort.

We note that the decision not to regulate the backset of rear head restraints has the effect of making our upgraded standard consistent with the ECE regulation on this point.

In addition to rear occupant comfort concerns, we note that our FRIA does not attribute any safety benefits to vehicle occupants as a result of regulating backset in rear seats. By contrast, we estimated that for front seats, the limit on backset would result in 15,272 fewer whiplash injuries each year. As explained in Section XVI of this notice, we based our estimates of benefits on either increased height or reduced backset, but not both. We could not combine effectiveness of increased height and reduced backset because this, in some instances, would result in “double-counted” benefits. For front seats, we attribute the benefits to the backset limit. We estimate that greater share of the safety benefits will come from the backset limit because many current vehicles already include taller front seat head restraints. For rear seats, we attribute the benefits to height because we anticipate that the greater share of the benefits will come from regulating the height of optional head restraints.

Adjustable backset suggestion.

Several seat and automobile manufacturers argued that, to accommodate occupant comfort, a 50 mm backset requirement should be supplemented with an allowance for backset to be adjustable to distances of up to 100 mm, so long as it could also be adjustable to a minimum setting of 50 mm. In contrast, most consumer groups voiced opposition to allowing a backset distance of up to 100 mm, even if it would be adjustable to a shorter distance of 50 mm. Advocates argued that the backset should be limited to 50 mm or less, and there should not be an allowance for an adjustable 100 mm backset, because it is commonly known that most occupants will not properly adjust their head restraints. Florida International University (FIU) students claimed that most occupants would simply leave their head restraints adjusted at a backset of 100 mm because of the lack of adequate consumer awareness. Johnson Controls was similarly opposed to an adjustable backset, stating that it is evident that most head restraints would be misadjusted. Johnson Controls stated that 60 to 80 percent of occupants do not properly adjust their head restraints. ICBC was similarly opposed to head restraints with adjustability beyond 50 mm, stating that it would lead to misadjustment and reduced effectiveness.

We were not persuaded to allow a head restraint system featuring adjustable backset mechanism that would allow as much as 100 mm of backset, even if such mechanism would be capable of achieving a 50 mm backset measurement. We agree with arguments put forth by ICBC and Advocates that the possibility of misadjustment is too great. In case of vertical adjustment, the height between the ears and the top of the head provides a clear target zone for adjustment. There is no such clear target adjustment zone for backset. Further, if a vertically adjustable front head restraint is adjusted to its lowest position, it still provides an acceptable level of protection at a height of 750 mm. If the head restraint is adjusted too high, it provides an obvious visual cue to the seat occupant. In the case of backset misadjustment, there would not be a minimally acceptable level of protection at 100 mm of backset, because such measurement does not provide sufficient protection against excessive head-to-torso rotation. Further, a head restraint with a misadjusted backset would not provide an occupant with an obvious visual cue, as most occupants are unaware of the necessity for proper backset adjustment. In sum, we conclude that allowing for an adjustable backset could end up defeating the purpose of the new backset requirement.

Seat back angle for backset measurement.

We are aware of certain variability concerns associated with backset measurement using the HRMD device with a SAE J826 manikin torso reference line angle of 25 degrees. We will refer to the torso reference line angle of the J826 manikin and seat back angle interchangeably. Concerns associated with the use of HRMD device are discussed in Section IX. The seat back angle of 25 degrees was chosen because it is on the edge of the range of normally selected seat back angles and would most likely be selected by larger occupants. ICBC, which developed the HRMD, designed it to be used at 25 degrees. Of course, for some fixed

position rear seats, this is not possible. The 25-degree angle is also consistent with the methods used by IIHS and RCAR for measurement of height and backset. ECE 17 does not specify a limit on backset, but for height measurement the seat back is set to 25 degrees unless the manufacturer's recommended seat back angle is specified. While several manufacturers stated that measuring head restraint height at steeper (

i.e.

, smaller) seat back angles result in smaller measured height, our own data indicate that reducing seat back angle by one degree results only in a 2 to 3 mm reduction in head restraint height measurement. We also find persuasive the information provided by ICBC stating that a ±1-degree error in torso angle results in a change in backset measurement of only ±3 mm.

We note that the 25-degree seat back angle in comparison to steeper angles represents a more stringent requirement for backset measurements because it maximizes the distance between the head and head restraint. However, a 25-degree angle is less stringent for measuring head restraint height. Indeed, if we decided to adopt the manufacturer's design seat back angle, typically around 23 degrees,

we would in fact be requiring even taller head restraints. Although we considered measuring height at a steeper angle than 25 degrees, we decided against it. Rather, we are adopting a single measurement angle for both height and backset in order to reduce unnecessary complexity in measurements and increase accuracy of testing results. We believe the 25-degree specification will not compromise safety for shorter or taller occupants. Finally, using the same angle for the measurement of backset and height for every seat, rather than the manufacturer's design seat back angle, will allow comparison of height and backset measurement from seat to seat.

SAE J1100—Motor Vehicle Dimensions. All 1999-2000 make and model data submitted to NHTSA. The data ranged from 18 to 28 degrees.

VIII. Measurement of Backset and Height

NHTSA proposed that compliance with the backset and height requirements be measured through use of the ICBC HRMD. The HRMD consists of a SAE J826 three-dimensional manikin with a head form designed by ICBC attached. The ICBC head form contains a probe that slides rearward until contact is made with the head restraint, thus allowing a backset measurement. For height measurement, the SAE J826 manikin is used without the HRMD. The SAE J826 manikin provides a scale that gives the distance from the H-point along the torso line, thus allowing a height measurement.

If the seat cushion adjusts vertically independently of the seat back, the measurements will be taken with the seat cushion adjusted to the most unfavorable position;

i.e.

, the position that minimizes head restraint height.

Although HRMD has a probe that makes it possible to measure head restraint height vertically down from the top of the HRMD, this probe will not be used because it is not consistent with measurement along the torso line.

Most vehicle manufacturers and seat suppliers 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. Johnson Controls, Nissan, Magna, Ford, VW, and GM commented 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. Additionally, DaimlerChrysler commented that NHTSA's own compliance procedure for Standard No. 208, involving the J826 manikin, allows for variability of ±12.5 mm for the Hybrid III test dummy's H-point in comparison to the J826 H-point and that the Hybrid III is a more biofidelic representation of a seated occupant. Ford stated that when measuring a head restraint reaching 800 mm, a manikin torso angle variation of ±1 degree produced a 28 mm variation in the backset measurement. Porsche stated that the HRMD device could not be properly positioned in the seats that have strong-contoured shape, therefore preventing accurate measurements. Honda provided data showing repeated backset measurement of a single seat by 3 test technicians. The largest range for any technician was 10 mm and the overall range of backset was 17 mm.

On the other hand, Transport Canada reported that a study commissioned by several Canadian insurance companies, conducted by Rona Kinetics and Associates, Ltd., entitled “Head Restraint Field Study,” concludes that HRMD is repeatable and an effective predictor of head restraint positions. Transport Canada has used HRMD for years and finds it to be a convenient and accurate tool.

In addressing accuracy concerns, ICBC said that the HRMD yields a level of accuracy of ±5 mm when used by competent, well-trained operators. ICBC stated further that manufacturers have historically had to accommodate similar tolerance levels with other compliance testing based on the H-point machine. Further, according to ICBC, 1 degree in seat back variance yields a deviation of no more than 3 mm as opposed to 13-28 mm as suggested by some commenters. In addressing Ford's comments on different measurement results for virtually identical vehicles, ICBC stated that the two seats, while identical in theory, had different upholstery materials (leather and cloth) and also had different stitching patterns. As a result, the deviation between two seat measurements was 5 mm, which ICBC noted was enough to warrant awarding two different vehicle head restraint ratings.

The SAE cautioned that the current H-point machine is undergoing considerable revision and the ICBC device could not be mounted on the new manikin. It argued that if the ICBC device were mandated, the manufacturers would be forced to use an otherwise outdated compliance device. Magna suggested that we consider the ASPECT (Automotive Seat and Package Evaluation and Comparison Tools) manikin as a compliance tool, instead of the HRMD.

According to several manufacturers, including Magna, Porsche and Honda, a more appropriate measurement methodology would utilize SgRP. The SgRP is a theoretical point in the vehicle, usually representing the most rearward normal riding or driving H-point, as determined by the manufacturer. Further, they requested that a CAD drawing be used to obtain the most precise height and backset measurements. Specifically, Magna recommended that we use a CAD design tool to measure the required head restraint height. Similarly, Porsche has asked us to consider virtual measurement methods using Ramsis software. Honda suggested that the HRMD assembly be translated into electronic data and the measurements be taken electronically.

UMTRI also recommended a height and backset measurement technique that uses the H-point as the reference. Once the H-point is established, a 165 mm sphere would be rolled vertically. The most rearward part of the sphere would map a path. From this path, the height of the head restraint and backset can be calculated at any height. The procedure could be done at any position of head restraint adjustment.

In response to the suggestion of alternative measuring devices, ICBC

commented that it developed the HRMD because there were no similar tools available to produce accurate and repeatable measurements. It claimed the HRMD is more biofidelic than other similar or proposed devices, because it has an articulating neck joint that approximates the C7-T1 joint (

i.e.

, the location on the spine between the most inferior cervical vertebra and the most superior thoracic vertebra). This allows the operator to approximate human posture at any seat back angle. The ICBC noted that there are 35 HRMD devices now in use, arguing this makes it a well-accepted compliance tool; the device is readily available from ICBC. Further, the HRMD represents a small cost for demonstrating compliance.

ICBC further stated that despite industry comments to the contrary, the ICBC device does not add extra weight to the H-point machine. The ICBC weight closely approximates the weight of the 50th percentile head and neck. No extra weight is added to the H-point machine because some upper torso weights are removed from the manikin to compensate for the ICBC device. Specifically, the HRMD with two “replacement weights” substitutes for 4 out of 8 H-point machine weights.

Generally, ICBC suggested that the HRMD device be used instead of a computer-based method of determining compliance. However, if some sort of electronic compliance were implemented, it believes Honda's proposal is preferable because it contemplates the use of “virtual” HRMD, which most closely replicates actual human seating positions. In response to SAE's concern with the forthcoming development of the revised J826 H-point machine, ICBC pledged full cooperation to ensure that HRMD can fit the future H-point machine.

RCAR submitted a test procedure it developed for head restraint measurement that uses the HRMD. It recommended using its measurement procedures in determining compliance with the new criteria.

Agency response:

Despite the objections of numerous commenters, we have decided to adopt the HRMD for our compliance tests. Under the current version of FMVSS No. 202, the manufacturers provide NHTSA with the theoretical location of the SgRP with respect to some vehicle reference point. The new rule eliminates the need for obtaining a theoretical point from the vehicle manufacturer, determined by a CAD technique, because the HRMD defines the H-point of the specific seat being measured. In addition, the H-point can be found for any position of seat cushion adjustment, thus allowing the worst-case head restraint height to be measured.

We conclude that the ICBC comments related to a CAD technique for determining head restraint geometry are the most compelling. Specifically, ICBC noted that various techniques suggested by the manufacturers all have the limitation of not measuring the actual seat, as it exists in the real world. Instead, they rely upon measurements made in a virtual or computer generated environment. The current FMVSS No. 202 height measurement technique has the same weakness, as it uses the SgRP determined by drawing techniques and a seat position defined by the manufacturer. While we appreciate the numerous benefits associated with CAD techniques in the design of vehicles and their components, we believe these techniques are not yet appropriate for a regulatory environment. Any CAD method would not only have to rely on an adequate model of the J826 manikin, but, even more importantly, an accurate representation of the vehicle seats. Each seat model would require extensive validation to assure that the CAD results would match the results achieved by direct measurement. A design change such as new upholstery foam or covering material would likely require a re-validation of the model. This type of process is appropriate for research or product development, but is not yet ready for regulatory purposes.

In regard to the backset and height measurement technique suggested by UMTRI, we conclude that the technique is useful to the extent it allows backset to be calculated for an occupant of any height rather than just for a 50th percentile male. However, we are not aware of any physical device currently available to map out the continuous backset. Thus, in order for the agency to adopt the UMTRI method, a CAD technique would have to be adopted, unless a new physical testing device is developed. We have rejected the use of CAD methods for the reasons specified above.

Numerous commenters questioned the accuracy of the HRMD device. Specifically, the manufacturers questioned repeatability of measurements and stated that the HRMD is incapable of accounting for foam, trim, actual H-point, temperature, and humidity variations. However, ICBC submitted data showing accuracy of ±5 mm. Because ICBC has a significant amount of experience in using the HRMD, its assertion that the overall level of repeatability of its device is within a ±5 mm, when used correctly, is persuasive.

We also conclude that ICBC provided adequate explanation for the discrepancy between the measurement results for Ford Taurus and Mercury Sable, a discrepancy that would not have been found using a CAD technique. Different upholstery and stitching patterns can result in different measurements. If these differences are significant, the difference in both height and backset may be significant. Further, a Transport Canada study concluded that the HRMD is repeatable and an effective predictor of head restraint position of humans. Transport Canada has used the HRMD for years and finds it to be a convenient and accurate tool. There are at least 35 HRMDs now in use, and the head form is readily available from ICBC.

We found that while measuring head restraint geometries with the HRMD for use in a cost study, the backset measurements varied by a total of 10 mm when NHTSA's Vehicle Research and Test Center (VRTC) repeated the measurement of a single vehicle seat 3 times. This is consistent with the ICBC statements showing ±5 mm accuracy. Further, experience indicates that greater familiarity with the device reduces the variability of measurements. Thus, the measurement variance shown in the Honda data (10 mm for 1 operator and 17 mm for 3 operators) may have been due to a lack of familiarity with HRMD.

Porsche stated that the HRMD device could not be properly positioned in the seats that have “strong-contoured shape,” therefore preventing accurate measurements. However, Porsche did not provide any data comparing the position of HRMD head form to the position of an actual occupant's head in one of its “strong-contoured shape” seats. We believe that Porsche must currently use the SAE J826 manikin to find the reference H-point position of the Hybrid III 50th percentile manikin for frontal barrier tests in FMVSS No. 208, and therefore has some familiarity with how to properly position the device. Generally, we believe that experienced operators will not encounter any difficulties in measuring seating structures with HRMD.

Several comments suggested that the HRMD device is insufficiently biofidelic. However, we are persuaded by ICBC's comments that HRMD is more biofidelic than other similar devices because it has an articulating neck joint that approximates the C7-T1 joint. This design feature allows the operator to level HRMD's head regardless of the seat back angle, similar to the posture of a human occupant, resulting in superior accuracy of backset measurement. While

we are aware that the SAE has updated the J826 manikin in the form of the ASPECT manikin in July 2002, this new device has yet to be evaluated by the agency for incorporation into FMVSS.

Based on the comments and analysis presented above, we have decided that the HRMD will be the measurement tool.

IX. Maximum Gap Allowance and Removability

a. Maximum Gap Allowance

The NPRM proposed allowing for gaps within the perimeter of the front (anterior) surface of head restraints in order to provide for better rearward visibility for drivers.

The NPRM proposed two types of maximum gap allowances. First, for both integral and adjustable head restraints, a gap within the perimeter of the head restraint could not exceed 60 mm. Because there may not be a clear distinction between the end of the seat back and the beginning of the head restraint in integral head restraints, compliance with this first gap limit is determined by measuring any point on the front surface of the seat back 540 mm above the H-point and within the minimum head restraint width. We note that ECE 17, Paragraph 5.8, similarly regulates gaps at heights above 540 mm.

The gap limits are applied between two vertical longitudinal planes, which are one half the minimum head restraint width from the head restraint centerline. Thus, any part of the front surface of the head restraint outside of the minimum width requirement is excluded from the gap limits.

The second type of gap allowance was between an adjustable head restraint in its lowest position and the seat. There were two levels of requirements. First, an adjustable head restraint in its lowest position must have some backset position in which the gap between the seat and the head restraint was less than 25 mm. Second, an adjustable head restraint in its lowest position, with the backset in any position of adjustment, must not have a gap between the head restraint and the seat back of greater than 60 mm.

The HRMD used for measuring backset has a probe that slides out of the center of the back of the head form. The probe is relatively thin laterally, and cannot adequately measure gaps within the perimeter of the head restraints and between the head restraint and the seat. Accordingly, the gaps were to be measured with a 165 mm diameter sphere placed against them.

Gaps within the perimeter of the restraint.

Nearly all industry commenters concurred with the proposal for a 60 mm limit for gaps within the perimeter of any head restraint, because it was consistent with ECE 17 requirements. There were no significant objections to the specific value of 60 mm. The Alliance indicated that while it did not know of any data supporting the need for the 60 mm gap limit for a seat with an integral head restraint, it did not object because the dimension matched the ECE limit. Honda, GM and DaimlerChrysler stated that they did not have any data addressing the 60 mm gap limits but supported harmonizing the requirement with ECE 25.

In contrast, Advocates argued against allowing gaps of any size, as it was not convinced by the NPRM's arguments pertaining to the proposed gap allowances.

Agency response:

NHTSA has adopted the 60 mm gap limit rather than allowing for gaps of any size in the perimeter of the head restraint, as is the case under the current standard. In doing so, NHTSA does not harmonize the final rule with the ECE regulation merely for the sake of harmonization, as Advocates alleged. Rather, the agency is harmonizing the requirement because while we believe that some gaps are beneficial for visibility, we also believe that gaps of excessive size can significantly reduce effectiveness of head restraints through effectively increasing backset. Absent evidence that the ECE 17, Paragraph 5.7 requirement is ineffective at balancing the need for adequate rearward visibility and a reduction in injuries, NHTSA is adopting the same 60 mm gap limit.

Gaps between seat back and adjustable restraint.

The Alliance stated that it did not understand why a limit of 25 mm would be placed on any gap between the top of the seat and the bottom of the head restraint. It stated that while the 25 mm gap limit is identical to the ECE 17 limit, the measurement procedure utilizing the 165 mm diameter sphere differs from that in the ECE regulation. ECE 17 only measures the distance directly between the bottom of the head restraint and the top of the seat back. The Alliance recommended NHTSA adopt a linear measurement technique employed by ECE 17.

Honda commented on gap requirements in ECE 25 instead of ECE 17, and the gap limits proposed in the NPRM. Specifically, Honda submitted a figure showing that its Accord sedan with the head restraint in its lowest position complies with ECE 25 with no gap between the top of the seat back and the bottom of the head restraint. However, the Accord would not meet the proposed gap limit, because its gap would measure 44.8 mm. That is, the Accord head restraint in its lowest position has a 44.8 mm gap in the front surface between the seat back and head restraint when measured with the 165 mm diameter sphere. Accordingly, Honda requested complete harmonization with the gap requirements in ECE 25, which would exclude use of the 165 mm sphere for this gap limit. Honda stated that some of its current seat designs would need drastic modifications in order to comply with the 25 mm gap limit, as measured with the 165 mm sphere.

GM remarked that if NHTSA considers gaps of 60 mm acceptable within a restraint, the need for a 25 mm gap limit between the top of the seat and the bottom of the head restraint is unclear. DaimlerChrysler said that the 25 mm gap limit, as applied to rear head restraints, could lead to an additional loss in visibility. DaimlerChrysler also stated that a head restraint making direct contact with the seat back with a 15 mm radius at the head restraint's bottom front contour and seat back's top front contour would create a gap of more than 25 mm. AIAM expressed its support for all the proposed gap limits except for the 25 mm limit on gaps between the seat and the head restraint for adjustable head restraints with adjustable backsets. In view of this, AIAM argued that unless NHTSA could show a safety necessity for backset adjustability, NHTSA should only mandate the head restraint specifications independent of backset adjustability, provided that the adjustability does not have a material effect on height. AIAM advocated, then, that the final rule should require that the gap be less than 25 mm at any position of backset adjustment, which is more stringent than the NPRM.

In contrast, Advocates opposed allowing gaps of any size between an adjustable head restraint and seat back in any position of adjustment. Johnson Controls expressed support for a universal 25 mm gap limit between the lower edge of a head restraint and the seat for both adjustable and integral head restraints.

Agency response:

In consideration of comments submitted by GM and other manufacturers, we have decided not to adopt the 25 mm maximum gap limit for adjustable head restraints in their lowest height position and a single position of backset adjustment. After considering the comments, NHTSA does not believe there is a safety benefit in measuring the smallest space between the bottom of an adjustable head restraint and top of the seat back because an occupant's head does not necessarily come into contact

with these areas. Instead, a limit on gaps will focus on gaps in the front surface of the head restraint,

i.e.

, the area designed to restrain an occupant's head in a rear impact collision. The maximum gap limit for adjustable head restraints in their lowest position and any backset position will be 60 mm. Thus, there is a single requirement for this type of gap, regardless of backset adjustability.

We note that all head restraints subject to this final rule must meet the backset limit of 55 mm irrespective of 60 mm gap allowances.

Gaps between seat back and raised restraint.

Comments were requested on whether there should be a maximum gap allowance between adjustable head restraints and the seat back when the restraint is in a raised position. NHTSA indicated in the NPRM that if such a maximum gap limit were adopted, most adjustable head restraints currently on the market would not meet it.

The Alliance and Johnson Controls said that they did not know of any data supporting the need for this limit or any data indicating that such a requirement would be appropriate. DaimlerChrysler commented that there is not any known safety benefit related to such a limit. When head restraints are misadjusted, DaimlerChrysler said, they are most often in the full down position. Because a maximum gap limit between the seat and head restraint in its highest position potentially would only benefit shorter drivers who would most likely be positioned in a seat with a head restraint in the lowest position, DaimlerChrysler surmised that the maximum gap allowance is unnecessary. Taller drivers, according to DaimlerChrysler, would face no risks from this gap because their potential risks exist in head restraints not positioned high enough, not in head restraints adjusted too high.

AIAM also commented with respect to the effect of a maximum gap limit on taller or shorter drivers. It commented that if a seat represents the lower stop of a head restraint for which the highest possible position is 800 mm, the gap could only be 50 mm unless a head restraint provides for positions higher than 800 mm. If higher positions are possible, AIAM asserted that such a head restraint would only be positioned higher than 800 mm when a taller person occupies the seat. AIAM acknowledged that there might be instances in which a shorter person sits in a seat with a head restraint adjusted in the higher position, but it commented that in such instances, the likelihood of injury to shorter occupants is unknown.

Advocates believed that NHTSA should require adjustable head restraint designs such that no gap would exist when the head restraint is placed in its uppermost position.

Agency response:

After considering the comments, NHTSA concludes that there is no need to adopt a maximum gap limit when the head restraint is in its uppermost position. Transport Canada data indicate that head restraints are usually improperly adjusted too low rather than too high. AIAM's comment suggests that any minimum gap limit could have the effect of eliminating head restraint designs providing positions higher than 800 mm, which would adversely affect the protection offered for taller adults.

b. Removability

The NPRM proposed prohibiting the removability of head restraints in front seats “solely by hand,” but allowed removability of rear seat head restraints in this manner. The NPRM noted that, given the lower occupancy rate of rear seats than of front seats, a rule allowing rear seat head restraints to be removed by hand might be warranted if it would have a positive effect on visibility.

A number of commenters opposed any prohibition against the removability of head restraints, front or rear. AIAM asserted that all head restraints should be removable by hand in order to improve rear vision, cargo carrying, and overall functionality. In addition, it contended that allowing removability by hand would help prevent permanent damage to head restraint mountings caused when occupants use tools to temporarily remove head restraints that are non-removable by hand. Nissan asserted that there are potential production difficulties arising from front head restraint non-removability. Installing a large seat fitted with a head restraint into a small vehicle, Nissan asserted, might be an arduous task.

Honda wanted all restraints to be removable by hand, out of concern that non-removable head restraints would limit seat design flexibility. Honda believed that a non-removability prohibition would prevent it from offering the “fully flat seat” option in its CRV model vehicle.

In alternative, Honda recommended that we allow head restraint removal by use of some tool included with the vehicle.

In contrast, some commenters supported prohibiting head restraints from being removable by hand. Magna expressed concern that if head restraints were removable, they might not be replaced or correctly reinstalled. Advocates believed that head restraint removal and misuse would be similar to occupants placing both arms over shoulder belts or placing shoulder belts behind their torsos, effectively defeating the safety purposes of the safety system. DaimlerChrysler concurred with making front seat head restraints more difficult to remove than rear seat restraints because of their safety benefits and the absence of a need to remove them for visibility and functionality reasons. DaimlerChrysler also agreed that there should be some means to remove front head restraints for purposes such as seat cover installation. However, DaimlerChrysler wanted the word “tool” to be interpreted as including the mechanism in their current vehicles requiring two hands to operate.

A majority of industry commenters wanted NHTSA to allow removability of rear head restraints in the final rule. Ford believed that removability of rear head restraints would allow occupants to fold seats to increase space and would reduce possible incompatibility with child restraints. Ford stated that while many vehicles are currently designed with head restraints that are removable by hand, Ford does not know of any data regarding misuse or improper adjustment of head restraints caused by hand removability. DaimlerChrysler believed that NHTSA should permit rear seat head restraint removability to facilitate increased vehicle utility and rearward visibility.

Agency response to comments on head restraint removability:

After considering comments, NHTSA decided to allow removability of head restraints solely by hand. However, for both front and rear optional head restraints, removal must be by means of a deliberate action that is distinct from any act necessary for adjustment. That is, the “action” required for removal must be distinct from that required for adjustment. For example, the head restraint may be removed by depressing a special button or operating a lever located somewhere on the head restraint or the seat back. However, the action involved in adjusting head restraints must be different. This insures that head restraints are not accidentally removed when being adjusted. The new removability requirement uses language very similar to that in ECE 17, Paragraph 5.13.

We are establishing the new head restraint requirements to ensure that vehicle occupants receive better protection from whiplash and related injuries. To achieve this purpose, the agency wants to take reasonable steps to increase the likelihood that a head restraint is available when needed. If head restraints were too easily

removable, chances are greater that they will be removed. That, in turn, increases the chances that the restraints might not be reinstalled correctly, if at all. By prohibiting removability without the use of deliberate action distinct from any act necessary for adjustment, the likelihood of inadvertent head restraint removal will be reduced, thus increasing the chances that vehicle occupants will receive the benefits of properly positioned head restraints.

While NHTSA wants to increase the likelihood that a head restraint is available when needed, we also want to ensure that head restraints, especially in the rear outboard designated seating positions, can be removed in order to improve rear visibility, child restraint accommodation, and cargo carrying capacity. In certain very limited circumstances discussed by DaimlerChrysler, it may also be necessary to remove front head restraints. We are also persuaded by AIAM's comments concerning potential damage to head restraint mountings and locking mechanism that could be caused by occupants using a tool to temporarily remove the head restraints. Further, we believe that unforeseen problems could arise if the tool provided by the manufacturer for the purpose of removing head restraints is lost or otherwise unavailable at the time the head restraint must be removed. Because of these concerns, we decided not to adopt a proposed requirement that would have mandated that head restraints could not be removed without the use of a tool.

We have considered Advocates' comments that head restraint removal would defeat the purpose of the safety device. We believe that out approach strikes a balance between the need to ensure that a head restraint is available when needed and the need to improve rear visibility, cargo carrying capacity and accommodate child restraints. Further, with respect to rear seats, prohibiting head restraint removal when no head restraint is required could have the effect of encouraging manufacturers to design vehicles without rear head restraints. Our preference is that when possible, manufacturers install optional rear head restraints.

c. Non-use Positions

In connection with its proposal to mandate rear head restraints, NHTSA proposed to address concerns about the potential effect of those head restraints on the driver's view to the rear by allowing them to be foldable or retractable if they met certain requirements. Specifically, if a head restraint was adjusted to a “non-use” position (any position in which a head restraint's minimum height was less than the proposed 750 mm height or its backset was more than the 50 mm proposed backset), it would have been required to either return automatically to its proper use position when a dummy representing a person was placed in the seat, or give a person who occupied the seat an “unambiguous physical cue” of the improper head restraint position by significantly altering the torso angle of the occupant. If the head restraint was designed to return automatically from a non-use position to a normal use position, this had to occur when either a 5th percentile female or a 50th percentile male test dummy was placed in the seating position. To determine if the head restraint in a non-use position provided an “unambiguous physical cue,” the SAE J826 manikin was to be placed in the seat position. The torso angle of the manikin would have been required to be at least 10 degrees closer to the vertical than when the head restraint was in a normal use position.

Industry commenters uniformly favored a final rule permitting non-use positions for rear head restraints. However, many stated that because non-use positions in current vehicle designs are obvious to occupants, NHTSA need not condition allowance of those positions upon either automatic repositioning or 10-degree torso angle displacement. GM contended that designing head restraints to fold forward into non-use positions is not always feasible, especially given the proposed 254 mm minimum rear head restraint width for bench seats. GM, Honda and others remarked that folding or retractable head restraints with automatic return capabilities might not be practical and could result in excessive cost.

Other commenters asked NHTSA to permit methods different from the 10-degree torso displacement angle to alert vehicle occupants to non-use head restraint positioning. Specifically, VW and Honda advocated harmonization with ECE 17, Paragraph 5.5.3.3, which allows for head restraints to be retracted into non-use positions as long as this position is “clearly recognizable to the occupant.” Similarly, Ford stated it believed that the NPRM's 10-degree proposed displacement rule would be excessively burdensome and would require substantial redesign of seating systems.

Several commenters opposed allowing non-use positions. State Farm suggested that NHTSA should only permit non-use positions for rear head restraints if NHTSA determines either visibility or child restraint incompatibility are issues meriting consideration. Advocates noted that automatically retracting or manually folding head restraints might malfunction or become stuck in a non-use position. Advocates opposed the proposal to the extent that it did not specifically require that non-use positions for rear head restraints remain limited to ones achieved by folding or retracting. Moreover, Advocates expressed doubt about the objectivity of the “unambiguous physical cue” as an occupant's indication of a non-use position, stating that the subjective standard would create the potential for ambiguous designs that would give rise to misuse.

Transport Canada and Honda asserted that forward-folding head restraint designs might be misused in that an occupant may sit in the seat without returning the head restraint to an in-use position. Honda commented that smaller occupants might not recognize that the seating position moved 10 degrees closer to vertical is a warning of a non-use position. Instead, according to Honda, smaller stature occupants might consider the more upright position comfortable without understanding that the head restraint was positioned for non-use. In addition, Transport Canada stated that the proposal to require manufacturers to design their head restraints so that the torso angle of the SAE J826 manikin at least 10 degrees changes when the head restraint is in a non-use position might bring about a low fulcrum, which would increase neck injury in a rear impact collision.

Agency response:

NHTSA does not believe that non-use positions for rear head restraints should be allowed without any limitations. Instead, there must be objective performance requirements established to reduce the chances of injuries stemming from misused head restraints. Accordingly, the final rule adopts non-use position requirements proposed in the NPRM, but with some modifications. Further, this rule changes the test procedure and the test device to be used in determining compliance. Specifically, we are adopting the following: (1) A head restraint in a non-use position must automatically return to a normal “use position” when the seat is occupied by a 5th percentile female dummy whose midsagittal plane is aligned within 15 mm of the head restraint centerline; or (2) a head restraint must be capable of manually rotating at least 60 degrees forward or rearward in a vehicle vertical longitudinal plane between the “use position” and the non-use position.

The final rule does not require that the non-use positions cause a 10-degree change of the torso angle of the J826 manikin. Our proposal was based on the premise that the non-use position should give the occupant an obvious physical cue when the head restraint is not properly positioned. We have reassessed this requirement in light of our decision not to mandate rear head restraints and to allow head restraints to be removable without the use of tools. Given those decisions, it would be incongruous to mandate a possibly complex seat mechanism to ensure that non-use positions provide a physical cue to the occupant in the form of a 10-degree change to the torso reference angle. The changes to the non-use position requirements will also address comments made by Ford, GM and Transport Canada with respect to complexity, inconvenience and possible neck injury risk increase associated with the proposed requirement of 10 degree change in the torso reference angle.

We note that our requirements remain consistent with the ECE 17, Paragraph 5.5.3.3 to the extent that it mandates that a head restraint be capable of achieving a non-use position that is “clearly recognizable to the occupant.” With respect to Advocates’ concerns that the “unambiguous physical cue” language in the NPRM was subjective, we note that unlike the ECE requirements, this rule provides an objective test procedure to assess the “clearly recognizable” factor. Specifically, if the head restraint is capable of rotating forward or rearward by at least 60 degrees to achieve a non-use position, it is deemed “clearly” in a non-use position. This restriction is necessary to clearly inform the occupant that the head restraint is available, but out of place.

The final rule does not require that the rear head restraint automatically rotates the full 60 degrees or that the head restraint remains in this fully retracted position. In order to meet the strength requirements of this final rule, a head restraint that rotates rearward would likely need to have some mechanism that releases the head restraint from the position intended for occupant use. Accordingly, the head restraint would only be placed in a non-use position because of a particular need. It is possible that some vehicle operators may not rotate such head restraint fully. However, we believe in most instances the rear head restraint would be rotated the entire 60 degrees because this would best accommodate the vehicle operator's particular interest in adjusting the head restraint to a non-use position.

For head restraints that automatically return to a use position when occupied, the final rule does not require the use of a 50th percentile male dummy in addition to the 5th percentile female dummy, as was the case in the NPRM. Based on our review of current sensing technology, we assume the head restraint systems that will be designed to automatically return to a normal use position when a seat becomes occupied will use weight or optically based occupant-sensing technology. Thus, the use of the taller and heavier 50th percentile male dummy would be redundant since it would be more difficult to detect the shorter and lighter 5th percentile female dummy.

In response to Transport Canada and Honda's concern with respect to fold-forward designs, we note that non-use positions can be achieved by means other than fold-forward head restraints. Further, in allowing this type of design, we anticipate that a forward-folded head restraint will provide both a physical and visual cue to the occupant to properly position the head restraint.

We believe Advocates' statement that automatic return head restraints may fail to function overstates the safety concern. Although such failures are possible, they can occur with any safety mechanism.

We note that Volvo uses such a design in their S60 and S80 sedans.

NHTSA concludes that the allowing for non-use positions will facilitate better rearward visibility because the manufacturers will be able to design optional rear head restraints that fold or retract when rear seats are unoccupied, encouraging manufacturers to install rear head restraints.

X. Position Retention

In the NPRM, we proposed two loading test procedures to ensure that the head restraints remain in their position of adjustment (lock) upon application of force. These test procedures ensure that the head restraints can withstand the forces associated with normal pressure applied upon the head restraint during ingress and egress, as well as in the event of a crash. We note that while the ECE 17, Paragraph 5.1.1 requires locks on adjustable head restraints, it does not mandate that these locks meet vertical and horizontal position retention requirements to insure their functionality. In contrast, we proposed vertical and horizontal position retention requirements to ensure test objectivity associated with retention lock requirements.

The first test provided for the vertical, downward application of force upon a head restraint when placed at its highest position of adjustment and not less than, but closest to 800 mm for front seats and 750 mm for rear seats. A head restraint with an adjustable backset must meet the height retention requirements in any position of adjustment. Under the proposed procedure, a small, 50 N initial load would first be applied to the head restraint to provide a reference position for the head restraint. The reference position would be measured to eliminate variability associated with the soft upholstery of the head restraint. Next, a larger load would be applied to test the locking mechanism. The load would be increased to 500 N and held for 5 seconds. The load would then be reduced to the level of 50 N, at which point the head restraint would be required to return to within 13 mm of the initial reference position.

The second test procedure provided for a rear (posterior—rear with respect to the direction that the seat is facing) application of force perpendicular to the torso line. Testing for this position retention requirement to the rear is performed in the context of the displacement and ultimate strength requirements. This test is performed at any position of backset adjustment (if applicable) with the height adjusted to not less than, but closest to 800 mm for front seats and 750 mm for rear seats. In this instance, the NPRM proposed that a load producing a 373 Nm moment be applied to the back pan about the H-point to establish a displaced torso reference line. Next, a force producing 37 Nm would be applied to the head restraint to provide a reference position. The load would then be increased until it produced 373 Nm moment about the H-point and this load would be held for 5 seconds. At this point, any displacement beyond the displaced torso reference line would be limited to 102 mm. The head restraint load would then be reduced back to the level of 37 Nm, at which point the head restraint must return to within 13 mm of the initial reference position. To satisfy the ultimate strength requirement, the head restraints must be capable of providing resistance to an 890 N load for a period of 5 seconds.

We stated in the NPRM that the 500 N downward force and 373 Nm

rearward moment are representative of the peak loads likely to be encountered in moderate to severe rear impacts. The agency has reviewed upper neck shear loading from 33 rigid moving barrier,

rear impact (48 km/h (30 mph)) FMVSS No. 301 tests and found the average maximum load caused by the head being loaded in the forward direction with respect to the torso is 351 N. This direction of shear load is a good indicator of head restraint loading on the head and, therefore, head loading on the head restraint. Thus, the 373 Nm rearward moment and 500 N downward force are representative of the peak loads likely to be encountered in moderate to severe rear impacts. We asked for comments on the appropriateness of load values proposed for the two tests as well as the role of the retention locks in preventing head restraint maladjustment.

For an 800 mm high head restraint, the 373 Nm moment is achieved by applying a load 65 mm below the top of the head restraint. Thus the applied load is 507 N = 373 Nm/0.735 m.

Several commenters disagreed with the proposed height retention test requirement. Johnson Controls commented that it is unaware of any situations in which head restraints would move downward during accidents and thus does not understand the need for the vertical position retention test. In its opinion, the new requirement would unnecessarily complicate the locking adjustment mechanism, which consumers already find hard to use. Other commenters requested that NHTSA alter or simplify its height retention requirement. GM recommended that the testing criteria require that the head restraints simply “remain in their adjusted position” after an application of the required loads. According to GM, a more specific requirement that the head restraint be within 10 mm of its initial position, after position retention tests, might be difficult to meet because of possible compression of the head restraint foam. Similarly, DaimlerChrysler stated that the proposed height-retention test is inadequate to account for low recovery rate of crushable “friendly” materials designed to cushion an occupant's head upon contact.

Both Magna Seating Systems and DaimlerChrysler submitted the same test data showing a vertical load test in which an upholstered head restraint returned to within 22 mm of its initial position. The same head restraint with the upholstery removed returned to within 1 mm of its initial position. According to DaimlerChrysler, instead of testing the adjustment mechanism integrity, the proposed test indirectly measures the entire seating system, which includes energy-absorbing components. Therefore, a more appropriate solution is to simply measure head restraint position at the adjuster mechanism. Additionally, DaimlerChrysler stated that 500 N vertical load for position retention test may be excessive and unnecessarily harsh, and may end up requiring manufacturers to produce seats that are unnecessarily rigid and would result in potential harm to the passengers.

The Alliance generally agreed with most aspects of the proposed head restraint loading procedure. However, it was not aware of any reasons for the 5-second “hold” requirement in the position retention test. The Alliance recommended that the “hold” requirement be completely stricken or, in the alternative, limited to one second. AIAM was likewise of the opinion that the stringent height retention requirements would in fact discourage adjustability, because a mechanism meeting such requirements would be unduly difficult to design and use. Therefore, it recommended that the height retention requirement be eliminated from the proposed rule.

Honda commented that the problem with the vertical load test procedure is the shape and initial position of the loading device. Honda believed that this would cause the loading sphere to slip off of the head restraint. Honda recommended that loading test for height retention requirement be performed using a flat plate as opposed to a head form. Honda commented that no further height retention position testing (other than upper most position) should be tested, because the upper most position can be regarded as the worst position.

VW stated, “[s]ome Volkswagen and Audi vehicles provide head restraint adjustment above 800 mm to accommodate tall occupants, but in this situation a locking system at the maximum height is not provided.” They requested that the height retention requirement not be applied to position of adjustment above 800 mm. They contended that when a seat back is folded the head restraint might interfere with the roof and cause damage to a locked head restraint.

Volkswagen also commented on the backset retention requirement. They asked that the agency clarify their interpretation that the initial reference position to which that the test device must return within 10 mm (now 13 mm in the final rule) is the position the test device obtains after the 37 Nm reference load. The agency confirms this interpretation of the test procedure.

In contrast, IIHS commented that the height retention test is necessary to prevent poor head restraint designs that, for example, tend to “fall” to their lowest position during normal road movement. IIHS cautioned that many occupants place their hand or arm on the head restraints in getting into and out of the vehicles, thus applying vertical and non-vertical pressure on the restraint mechanism.

There were no comments regarding the likelihood of misadjustment due to the absence of retention locks. There were no comments regarding the horizontal displacement requirement, other than the IIHS comment that the NPRM did not propose a horizontal loading requirement.

Agency response:

We have decided to adopt the position retention tests, both in the vertical and rearward directions, largely as proposed. As previously stated, ECE 17 requires locks on adjustable head restraints but does not mandate that these locks meet vertical and horizontal position retention requirements to insure their functionality. However, we find it necessary to require a certain minimal level of performance to ensure that the retention locks perform their function. Accordingly, the vertical and horizontal position retention requirements of this final rule apply to all front outboard head restraints and voluntarily installed rear outboard head restraints.

We proposed performance requirements for adjustable head restraints to assure that they remain locked in a specific position and are not unduly difficult to properly adjust. A 1982 NHTSA study found that the effectiveness of integral head restraints was greater than adjustable head restraints. The study concluded that the difference in effectiveness was due, in part, to adjustable head restraints being improperly positioned. Furthermore adjustable restraints can be pushed down inadvertently during occupant ingress and egress, and can collapse in a collision. Adjustment retention locks can mitigate this problem by helping to retain the adjusted position. Our new height and backset requirements are expected to improve performance of all head restraints. The performance of adjustable head restraints will be further improved if steps are taken to ensure that a restraint remains locked in a position selected by the user.

Today's rule requires that the head restraints remain within 13 mm of their vertical and horizontal position under the application of a downward and rearward force. For front seats, the height position retention requirements must be met at any backset position of adjustment and with the head restraint at a height not less than, but closest to 800 mm, and at the highest position of vertical adjustment. For optional rear seats, the height position retention requirements must be satisfied at a height not less than, but closest to 750 mm and at the highest position of vertical adjustment. The horizontal position retention requirements must be met at the height of 800 mm for front

head restraints and 750 mm for rear head restraints.

We are not persuaded by the arguments presented by GM and the Alliance related to the load hold time of five seconds. These commenters argue that a 5 second hold time is not consistent with ECE 17 requirements. Instead, they suggest a one second limit. We believe the ECE requirements are insufficient in this regard in that they do not specify a loading rate or hold time. Despite our attempts to bring the new rule into harmony with the ECE regulations when adopting a requirement already covered by the ECE, there are instances in which we need to further clarify the test compliance procedure to provide an objective measurement, as required by statute. This is one of those instances. We do not believe a 5 second hold period is onerous and have adopted it as part of the final rule. We further note availability of strong and properly functioning retention locks should not have any negative effect on occupants' ability to properly adjust their head restraints.

We disagree with VW's objection to head restraints locking in the highest adjusted position above 800 mm. To the extent that such an adjustment position is provided, it would be intended to protect the tallest occupants. However, without the ability to lock in this position, the head restraint could slip down to the 800 mm position or perhaps even lower during normal use, or in a rear impact. Thus, the head restraint would not offer the intended protection, while giving these taller occupants the impression that they are well protected. We are not persuaded by Volkswagen's argument that the locking mechanism may be damaged if the front seat head restraint comes in contact with the vehicle roof when folded forward for rear seat access. We acknowledge that in some vehicles this interference between the roof and head restraint may exist. In fact, such interference may exist between rear seat head restraints and more forward seats. However, we are not convinced that such contact would be damaging to the locking mechanism. If a manufacturer were concerned about damage to their locking mechanism, two solutions would be to either increase the robustness of the lock or to decrease the spring load in the seat back folding mechanism. Another design alternative discussed above in the context of non-use positions, although more mechanically involved, would be a design that disengages both the seat back and head restraint simultaneously.

We proposed a 10 mm performance limit on the return position of the actual loading device to the reference point because we considered this to be the most objective method of determining the actual performance of locks. Some vertical loading data provided by the industry indicated a return position as much as 22 mm from the initial position. No similar data were provided for the horizontal loading test. In order to verify that the performance value selected for the position retention requirement is reasonable, we performed a series of static tests on several seats. The tests were performed at General Testing Laboratories (GTL), under the FMVSS No. 202 compliance-testing contract. The tests were performed in January 2002, on five MY 2001 vehicles.

The test program assessed the ability of current head restraint designs to comply with the position retention requirements. We tested feasibility of the 10 mm limit on displacement from the initial position. Both the height retention and backset retention were tested. (

See

Table 1.) All head restraints were vertically adjustable and one (Mercedes E320) had rotational adjustment.

For complete test results, please see Docket No. NHTSA-2000-8570-60, 61, 62, 63, 64.

Table 1 shows the results of the height position retention tests and Table 2 shows the result of the backset position retention tests. One determination made by analysis of the test results was that the head restraint should not be allowed to displace more than 25 mm during the application of a pre-load to account for foam compression and other mechanical tolerances in the head restraint attachment as well as the situation in which the locking mechanism is so weak it cannot resist the preload.

The test results suggest that the backset displacement is less than the height displacement if the characteristics of the vehicle seat are accounted for. Therefore, if a single compliance value is selected for both the backset and height retention, we believe it is reasonable to allow the results of the height retention tests to drive the selection. However, if one does not account for seat characteristics, the horizontal displacement may be larger because of those characteristics.

Based on this limited data set, we believe that it is reasonable to alter the position retention tests to allow the seat back frame to be braced. Further, we have determined that the displacement limit after full load and return to preload should be increased to 13 mm from 10 mm. We believe using the limit of 13 mm would allow most vehicles to comfortably meet the requirement for both the height and backset retention. Therefore, we do not agree with DaimlerChysler's comments that suggested the 500 N vertical load for the position retention test is excessive.

Table 1.—Height Position Retention, Final Displacement Values (mm)

Reference load

Vehicle model

Final displacement

(mm)

50 N—not braced

Mercedes E320

6.4

50 N—not braced

Honda Civic

21.8

50 N—braced

Toyota Echo

11.4

100 N—not braced

Dodge Stratus

24.0

100 N—braced

Buick LeSabre*

Moved at Reference Load

†

* Detents but no locking mechanism.

†

No lock.

Table 2.—Backset Position Retention, Final Displacement Values (mm)

Reference load

Vehicle model

Final displacement

(mm)

50 N—not braced

Mercedes 320.

10.9‡

50 N—not braced

Honda Civic.

10.6

50 N—braced

Toyota Echo.

6.9

100 N—not braced

Dodge Stratus.

24.0

100 N—braced

Buick LeSabre*.

20.3†

‡ Rotational Adjustment.

* Detents but no locking mechanism.

† No Lock.

In response to comments provided by Honda, we believe that the vertical load test can be improved by replacing the loading sphere with a loading cylinder measuring 165 mm in diameter and 152 mm in length. We believe that any potential slippage of the head restraint with respect to the loading sphere, if it were to occur, would be primarily in the longitudinal direction. Since the long axis of the cylinder will be oriented in the vehicle longitudinal direction, the potential of slippage will be substantially reduced. Further, we have no experience with using a flat plate as the loading device, while the loading cylinder is currently an option in FMVSS No. 202. The cylinder is to be loaded at the point on the head restraint with the greatest vertical position, rather than at the “top” as previously defined in the standard. The term “top” has been defined as the highest point of the head restraint at which a plane that is perpendicular to the torso reference line of the J826 manikin intersects the head restraint. For the backset position retention loading test, however, the lower edge of the cylinder may inhibit the return of the head restraint during the unloading phase. Therefore the loading sphere, positioned perpendicular to the torso line, will be kept for this test.

We believe that DaimlerChrysler's comments related to upholstery crush and Honda's comments related to the loading sphere slipping might have merit. However, we disagree with the commenters who have suggested that these issues can be resolved by simply specifying that the head restraint stay in its pre-load adjusted position. Although similar wording is used in other regulations, including Standard No. 207, such a performance requirement can in certain instances be difficult to enforce. We acknowledge that removing the head restraint upholstery and loading only the underlying structure would make it easier to determine lock failure and would remove the foam variability from the test. However, this would not be a realistic way of loading the head restraint and may, in fact, change the path of loading. We also note that measuring the movement of the loading device instead of directly measuring the head restraint (pre- and post-condition) produces more accurate measurements for compliance purposes.

We believe that the proposed height and backset position retention requirements are comprehensive and that requirements for other positions than those mentioned above are unnecessary and would not result in significant additional safety benefits. We note, however, that manufacturers are not precluded from providing additional lockable positions within the range of the head restraint adjustment.

XI. Energy Absorption

The NPRM proposed that a specified area of the head restraint would have to limit the deceleration of a 6.8 kg mass impactor, traveling at 24.1 km/h, to 80 g's. The impactor was a free-motion head form. In addition, we proposed that any portion of the head restraint that was outside of the impact area and that had a radius of curvature of less than 5 mm would be required to pass the energy absorption test. We requested comments on whether a free-motion head form was an appropriate testing device and whether the radius of curvature requirement was necessary.

Impactor.

Industry commenters were unanimous in their desire for the use of the pendulum impactor instead of the free-motion head form. Johnson Controls and Honda suggested that the use of a pendulum impactor, as specified in ECE 17, Paragraph 5.1.3, is preferable to the use of a free-motion impactor for the energy absorption compliance testing. According to Honda, the primary reason for the desirability of the pendulum impactor is that conducting testing using this device would allow the manufacturers to use existing testing facilities and equipment.

Agency response:

In proposing the free-motion head form, we intended to simplify the ECE energy absorption test by making the impactor similar to that used for the upper interior impact portion of Standard No. 201. We also attempted to assure consistency with the ECE testing results by making the mass of the proposed free-motion impactor identical to that of the ECE 17 pendulum impactor (6.8 kg).

We have decided to adopt a linear impactor, as opposed to a pendulum impactor or free-motion head form, as the compliance tool. Our decision was based on several factors. First, the use of a pendulum impactor could prevent us from running compliance tests on the actual vehicle without significant vehicle alteration, because of the interference of the vehicle interior with that type of impactor. If, as suggested by the manufacturers, a pendulum impactor were used, the seats would either have to be removed to allow for the pendulum swing or the roof of the vehicle would have to be cut open. Because of the cost involved, we often use the same vehicle to run multiple compliance tests. Removing seats or cutting into the vehicle to accommodate test equipment would limit our ability to run subsequent compliance tests for other standards.

Second, the differences between the linear impactor and free-motion impactor are insignificant in terms of their ability to measure compliance with the energy absorption requirement. The linear impactor is constrained so that it moves along a line, while the free-motion impactor is free to rotate upon impact or to have a rotation imposed upon it at the time of launch. This unconstrained motion is beneficial for use with types of impactors that have an irregular surface, such as a surface simulating a human face. However, since the impactor for the energy absorption test is spherical, there is no need for the free motion.

Third, the linear impactor is easier to target than the free motion head form, leading to more repeatable results. Currently, a linear impactor is used for the instrument panel and seat back impact testing under Standard No. 201. Fourth, we believe that the results obtained from a linear impactor will in fact be very similar to the results obtained from a pendulum impactor or free-motion impactor because the impactors have the same mass and impact velocity.

Radius of curvature.

We proposed an energy absorption requirement for all surfaces with less than a 5 mm radius of curvature to eliminate potential sources of high-pressure contacts between occupants and head restraints. We have decided against adopting this requirement.

The Alliance stated that it is unaware of a need for a “radius of curvature of less than 5 mm requirement,” and recommended its deletion. Honda commented that the ECE 25 requirement for 5 mm radius of curvature limit is intended to apply to unpadded structures or structures padded with material softer than 50 Shore A hardness.

Agency response:

In our opinion, the burden associated with the enforcement of this requirement outweighs its benefits. In order to determine that structures with the soft upholstery have radii of less than 5 mm, we would be forced to remove the soft upholstery. Thereafter, a second, upholstered head restraint would have to be subjected to the impact test. No commenter provided information supporting such a requirement. Accordingly, we are not adopting our proposal regarding areas on the front surface of the head restraint that are outside of the impact area.

As previously discussed, this final rule does not mandate rear outboard head restraints. However, this rule does require that the voluntarily installed rear outboard head restraints meet the energy absorption requirements discussed above.

XII. Issues Unique to Rear Head Restraints

a. Optional Head Restraints for Rear Seating Positions

The NPRM proposed mandating head restraints for all rear outboard seating positions, but asked whether NHTSA should limit the final rule to front seating positions. This question was based on visibility concerns as well as the lower safety benefits that would be obtained from rear seat head restraints, as compared to those from front seat head restraints, given lower occupancy rates for rear seats. Most of the industry commenters stated that, consistent with ECE 17, rear head restraints should remain optional. ECE 17 treats rear head restraints as an option, but regulates them if they are installed in a vehicle. Johnson Controls reasoned that because the dangers for rear seat occupants are less than those for front seat occupants, rear head restraints should not be mandated. GM, the Alliance, and others believed that rear head restraints should be an option because of rear seats' lower occupancy rates, occupancy of rear seats usually by shorter individuals, potential child seat interference with rear head restraints, and the potential reduction of direct and indirect rear vision. In supplemental comments, GM stated its concern that rear seat head restraints will affect its ability to comply with the requirements of FMVSS No. 111,

Rear View Mirrors.

GM's concern that rear head restraints will affect compliance with FMVSS No. 111 is not warranted because head restraints are an allowable obstruction. In addition, if the rear window field of view requirements are not met, compliance could be achieved by adding passenger side outside mirrors. The

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