[Federal Register Volume 89, Number 136 (Tuesday, July 16, 2024)]
[Proposed Rules]
[Pages 57998-58038]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-15390]



[[Page 57997]]

Vol. 89

Tuesday,

No. 136

July 16, 2024

Part II





Department of Transportation





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 National Highway Traffic Safety Administration





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49 CFR Part 571





Federal Motor Vehicle Safety Standards; Seating Systems; Proposed Rule

  Federal Register / Vol. 89 , No. 136 / Tuesday, July 16, 2024 / 
Proposed Rules  

[[Page 57998]]


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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. NHTSA-2024-0001]
RIN 2127-AM53


Federal Motor Vehicle Safety Standards; Seating Systems

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

ACTION: Advance notice of proposed rulemaking.

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SUMMARY: Through this document, NHTSA fulfills the statutory mandate in 
section 24204 of the Infrastructure Investment and Jobs Act (IIJA), 
which directed the Secretary of Transportation to issue an advanced 
notice of proposed rulemaking to update Federal Motor Vehicle Safety 
Standard No. 207, ``Seating systems.'' NHTSA also partially grants 
rulemaking petitions submitted by Kenneth J. Saczalski of Environmental 
Research and Safety Technologists (ERST) and by Alan Cantor of ARCCA, 
Inc. (ARCCA), which sought changes to the Federal Motor Vehicle Safety 
Standards (FMVSS) petitioners stated would improve the safety of 
children during rear-end crashes. NHTSA denies a petition from the 
Center for Auto Safety (CAS), which sought to require additional 
warnings instructing adults regarding which rear seating position to 
place children.

DATES: Comments must be received no later than September 16, 2024. The 
Saczalski and Cantor petitions are granted in part and the CAS petition 
is denied as of July 16, 2024. See ADDRESSES and Section VIII. Public 
Participation for more information about submitting written comments 
and reviewing comments submitted by other interested parties.

ADDRESSES: You may submit written comments, identified by docket number 
or RIN, by any of the following methods:
     Federal eRulemaking Portal: Go to https://www.regulations.gov. Follow the online instructions for submitting 
comments.
     Mail: Docket Management Facility, U.S. Department of 
Transportation, 1200 New Jersey Avenue SE, Room W12-140, Washington, DC 
20590-0001.
     Hand Delivery or Courier: 1200 New Jersey Avenue SE, West 
Building, Ground Floor, Room W12-140, Washington, DC, between 9 a.m. 
and 5 p.m. E.T., Monday through Friday, except Federal holidays. To be 
sure someone is there to help you, please call 202-366-9826 before 
coming.
    Instructions: For detailed instructions on submitting comments and 
additional information on the rulemaking process, see the Public 
Participation heading of the SUPPLEMENTARY INFORMATION section of this 
document. Note that all comments received will be posted without change 
to https://www.regulations.gov, including any personal information 
provided. Please see the ``Privacy Act'' discussion in Section IX. 
Regulatory Analyses and Notices.
    Confidential Business Information: If you claim that any of the 
information or documents provided to the agency constitute confidential 
business information within the meaning of 5 U.S.C. 552(b)(4), or are 
protected from disclosure pursuant to 18 U.S.C. 1905, you must submit 
supporting information together with the materials that are the subject 
of the confidentiality request, in accordance with part 512, by email 
or secure file transfer to the Office of the Chief Counsel, Litigation 
and Enforcement Division. Do not send a hardcopy of a request for 
confidential treatment to NHTSA's headquarters.
    Your request must include a request letter that contains supporting 
information, pursuant to Sec.  512.8. Your request must also include a 
certificate, pursuant to Sec.  512.4(b) and part 512, appendix A.
    You are required to submit one unredacted ``confidential version'' 
of the information for which you are seeking confidential treatment. 
Pursuant to Sec.  512.6, the words ``ENTIRE PAGE CONFIDENTIAL BUSINESS 
INFORMATION'' or ``CONFIDENTIAL BUSINESS INFORMATION CONTAINED WITHIN 
BRACKETS'' (as applicable) must appear at the top of each page 
containing information claimed to be confidential. In the latter 
situation, where not all information on the page is claimed to be 
confidential, identify each item of information for which 
confidentiality is requested within brackets: ``[ ].''
    You are also required to submit to the Office of the Chief Counsel 
one redacted ``public version'' of the information for which you are 
seeking confidential treatment. Pursuant to Sec.  512.5(a)(2), the 
redacted ``public version'' should include redactions of any 
information for which you are seeking confidential treatment (i.e., the 
only information that should be unredacted is information for which you 
are not seeking confidential treatment).
    For questions about a request for confidential treatment, please 
contact Dan Rabinovitz in the Office of the Chief Counsel at 
[email protected] or (202) 366-8534.

FOR FURTHER INFORMATION CONTACT: Mr. Tyler Brosten, Office of 
Crashworthiness Standards (Telephone: 202-366-1740; Email: 
[email protected], Facsimile: 202-493-2739), or Mr. Eli Wachtel, 
Office of Chief Counsel (Telephone: 202-366-2992; Email: 
[email protected]). You may mail these officials at: National Highway 
Traffic Safety Administration, 1200 New Jersey Avenue SE, Washington, 
DC 20590.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Introduction
II. Occupant and Seat Back Dynamics and Field Data on Rear Impact 
Crashes
    A. FARS and CRSS Data Analysis
    B. CISS Data Analysis
    C. Field Data Analyses From Relevant Literature
III. Statutory and Regulatory Background
    A. The Safety Act and the Infrastructure, Investment and Jobs 
Act
    B. Regulatory History of FMVSS No. 207 and FMVSS No. 202, and 
Associated Research/Analyses
    1. 1963--SAE Recommended Practice for Seats
    2. 1967--Publication of FMVSS No. 207, Seating Systems
    3. 1968--Publication of FMVSS No. 202, ``Head Restraints''
    4. 1969--Report on Seat Safety Studies at ITTE
    5. 1974--Notice of Proposed Rulemaking (NPRM) To Revise FMVSS 
No. 207
    6. 1978--NHTSA Publishes a Request for Comment on Rulemaking 
Priorities
    7. 1989--NHTSA Receives Petitions for Rulemaking on Revisions to 
FMVSS No. 207
    8. 1992--2000 NHTSA Publishes a Request for Comment on Possible 
Revisions to FMVSS No. 207, Grants Two Petitions and Conducts 
Research
    9. 2004--NHTSA Issues Final Rule Upgrading FMVSS No. 202, Head 
Restraints
    10. 2004--NHTSA Terminates Rulemaking on FMVSS No. 207, Seating 
Systems
    11. Further Regulatory Changes Since 2004
IV. Review of Additional Literature
    A. Occupant Dynamics
    B. Rear Impact Protection Technology
    C. Non-Contact Injuries
    1. Neck Injuries
    2. Thorax Injuries in High-Speed Rear Impacts
    D. Summary
V. Petitions for Rulemaking at Issue in This Document
    A. Statutory and Regulatory Background
    B. Petition of Kenneth J. Saczalski
    1. FMVSS No. 207, Seating Systems
    2. Use of FMVSS No. 301, ``Fuel System Integrity,'' To Test 
Seats
    3. FMVSS No. 213, Child Restraint Seats
    C. Petition of Alan Cantor
    1. Use of FMVSS No. 301, ``Fuel System Integrity,'' To Upgrade 
FMVSS No. 207
    2. Rearward Rotation Limit and Structural Symmetry Requirement

[[Page 57999]]

    3. Additional Dynamic Testing and NCAP Implementation
    4. FMVSS No. 209, Seat Belt Assemblies
    D. NHTSA's Analysis of Saczalski and Cantor Petitions
    1. Analysis of Data and Research Provided by Cantor and 
Saczalski Regarding Safety Need
    2. Rear Structure Intrusion
    3. Cost and Practicability
    E. Assessment of the Specific Recommendations by Cantor and 
Saczalski
    1. Matters on Which NHTSA Is Granting the Petitions
    2. Matters on Which NHTSA Is Denying the Petitions
    F. Conclusion of NHTSA Assessment of Cantor and Saczalski 
Petitions
    G. Center for Auto Safety (CAS) Petition
    H. Analysis of CAS Petition
VI. Unified Approach to Rear Impact Protection
    A. Introduction
    B. FMVSS No. 207
    C. Analysis of Approaches To Updating Standards for Occupant 
Protection in Rear Impact
    1. Seat Back Strength and Other Mechanical Properties
    2. Test Parameters
    3. Quasi-Static Testing
    4. Dynamic Testing
    D. Crash Avoidance Technology
VII. NHTSA's Forthcoming Research
    A. Field Data Analysis and Market Research
    B. Test Procedure Assessment
    1. High-Speed Test
    2. Exploratory Testing
    3. Low-Speed Test
    C. Parametric Modeling
    D. ATD and Injury Risk Function Development
    E. Cost Analysis
    F. Summary
VIII. Public Participation
    A. How can I inform NHTSA's thinking on this rulemaking?
    B. How do I prepare and submit comments?
    C. How can I be sure that my comments were received?
    D. How do I submit confidential business information?
    E. Will the agency consider late comments?
    F. How can I read the comments submitted by other people?
IX. Regulatory Analyses and Notices
    A. Executive Order (E.O.) 12866, E.O. 13563, and E.O. 14094 and 
DOT Regulatory Policies and Procedures
    B. Paperwork Reduction Act
    C. Privacy Act
    D. Plain Language
    E. Regulation Identifier Number (RIN)
X. Conclusion

I. Introduction

    As part of its safety mission, NHTSA issues Federal Motor Vehicle 
Safety Standards (FMVSSs) \1\ and other regulations for new motor 
vehicles and motor vehicle equipment to save lives, prevent injuries, 
and reduce economic costs due to road traffic crashes. All FMVSSs must 
meet the requirements of the National Traffic and Motor Vehicle Safety 
Act of 1966 (the ``Safety Act'').\2\ That is, they must ``be 
practicable, meet the need for motor vehicle safety, and be stated in 
objective terms.'' \3\ On November 14, 2021, the Infrastructure, 
Investment and Jobs Act (IIJA; Pub. L. 117-58 \4\) was passed. Section 
24204 of IIJA, ``Motor Vehicle Seat Back Safety Standards,'' directs 
the Secretary of Transportation to issue an advance notice of proposed 
rulemaking (ANPRM) within two years to update 49 CFR 571.207. The 
publication of this ANPRM fulfills this statutory mandate.
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    \1\ The FMVSS are codified in 49 CFR part 571.
    \2\ 49 U.S.C. 30101.
    \3\ 49 U.S.C. 30111(a). The Secretary must also (1) ``consider 
relevant available motor vehicle safety information; (2) consult 
with the agency established under the Act of August 20, 1958 (Pub. 
L. 85-684, 72 Stat. 635), and other appropriate State or interstate 
authorities (including legislative committees); (3) consider whether 
a proposed standard is reasonable, practicable, and appropriate for 
the particular type of motor vehicle or motor vehicle equipment for 
which it is prescribed; and (4) consider the extent to which the 
standard will carry out'' the purpose of the Safety Act. 49 U.S.C. 
30111(b). The purpose of the Safety Act is to ``reduce traffic 
accidents and deaths and injuries resulting from traffic 
accidents.'' 49 U.S.C. 30101.
    \4\ Public Law 117-58.
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    FMVSS No. 207 establishes requirements for seats, seat attachment 
assemblies, and their installation in passenger cars, multipurpose 
passenger vehicles, trucks designed to carry at least one person, and 
buses.\5\ The standard, among other things, sets minimum requirements 
for the strength of the seat back and its associated restraining 
devices and adjusters.\6\ While in its rearmost position, a seat back 
must withstand a rearward moment (torque) of 373 Newton-meters (Nm) 
(3,300 Inch-pounds (in-lb)), applied by a horizontal force measured 
vertically from the seating reference point.\7\ The standard also 
contains a test procedure. The test specifies an application of a 
rearward force on the uppermost cross member of the seat back 
structure, that results in a moment applied to the attachment (often 
the recliner mechanism) of the seat back and the remainder of the seat 
structure.
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    \5\ 49 CFR 571.207 S1 and S2.
    \6\ FMVSS No. 207 also contains provisions dictating the 
strength of seat attachments to the vehicle in both the front and 
rear directions. For the purposes of this ANPRM, ``strength'' with 
respect to seat backs refers to the maximum rearward moment or force 
a seat back is able to withstand. ``Stiffness'' refers to the 
resistance of the seat back to any (or a specified) amount of 
deformation and deflection. Stated another way, ``stiffness'' can be 
thought of as the increase in resistive force or moment per unit 
deformation or rotation. Rigidity is the characteristic of a 
structure, such as a seat back, exhibiting relatively limited 
deformation when exposed to a force. Rigid and yielding seat back 
structures are opposites.
    \7\ 49 CFR 571.207 S4.
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    Although FMVSS No. 207 sets the minimum seat back strength 
requirement, since 1968 the de facto minimum requirement for seat back 
strength has effectively been set by FMVSS No. 202 (now 202a), ``Head 
restraints.'' \8\ This standard requires head restraints and 
establishes requirements for them to reduce the severity of neck 
injuries in rear impact crashes. Currently, FMVSS No. 202a requires a 
fully extended head restraint to withstand an 890 Newtons (N) (200 
pound force (lb-f)) rearward load for 5 seconds applied 65 millimeters 
(mm) (2.5 inches (in)) below its top when adjusted to its highest 
position, which must be at least 800 mm.\9\ This creates an effective 
torque requirement on the seat back of 654 Nm (5,790 in-lb), where 654 
= 890*(0.8-0.065), significantly higher than the 373 Nm (3,300 in-lb) 
required by FMVSS No. 207.
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    \8\ The head restraint and seat back are interconnected parts of 
the seating system.
    \9\ 49 CFR 571.202(a) S4.2.7.
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    In addition to the requirement in IIJA, this ANPRM addresses three 
petitions for rulemaking NHTSA received requesting various amendments 
to the FMVSS related to the deformation of seat backs in rear 
impacts.\10\ Two of the petitioners, Kenneth J. Saczalski of ERST. and 
Alan Cantor of ARCCA requested that the agency increase the strength 
requirements for seat backs in the front row. They argue that seats 
that comply with the current standard may yield excessively during a 
crash, which can lead to spinal cord and brain injuries due to contact 
between the seated occupant's head and vehicle structures in the rear 
seat compartment. In addition, they state that under the current 
standard, in certain higher speed rear end crashes, a seat could yield 
to the point that the seat becomes fully reclined (hereinafter 
described as ``seat back failure''). This may cause a belted occupant 
in the front seat to slide underneath the seat belt, leading to 
ejection into the rear seat space or outside the vehicle. (The 
petitioners refer to this phenomenon as ``ramping.'') Ramping poses 
injury risk to occupants seated directly behind the occupied front 
seat. In addition, the petitioners have asked NHTSA to revise other 
FMVSSs in ways that they stated would mitigate the injurious effects of 
excessively yielding seat backs. This ANPRM seeks to further develop 
the

[[Page 58000]]

record on occupant protection in rear impacts to inform a potential 
future rulemaking. As explained in section V., this document grants 
these petitions in part.
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    \10\ These petitions, dated October 28, 2014 (Environmental 
Research and Safety Technologists, Inc.), and September 28, 2015 
(ARCCA), are available in the rulemaking docket at https://www.regulations.gov/.
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    The third petitioner, CAS, requested the addition of warning 
language to child restraint system labels and owner's manuals to warn 
parents against placing a child behind an occupied front seat.\11\ As 
explained in section V.H., this document denies this petition.
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    \11\ This petition, dated March 9, 2016, is also available in 
the rulemaking docket at https://www.regulations.gov/.
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    IIJA requires that NHTSA issue an ANPRM to update FMVSS No. 207. 
Congress stated, however, that an update must be consistent with the 
considerations described in 49 U.S.C. 30111(b) of the Safety Act and 
issued pursuant to the Safety Act. Therefore, it must be practicable, 
meet the need for safety, and be stated in objective terms as provided 
in 49 U.S.C. 30111(a). This ANPRM discusses issues that have 
historically contributed to the complexities of regulatory action on 
seating systems.
    As outlined in the regulatory and research review below, a major 
challenge in NHTSA's efforts to set standards for rear impact 
protection relates to the determination of whether a seat should yield, 
thereby reducing forces acting on the seat occupant, or be stiffer, and 
thus prevent rare occurrences like ramping or interaction with other 
occupants. Finding the appropriate balance inherent in rear impact 
protection is a theme and central debate in much of the research and 
analysis conducted on this issue.
    Complicating this question is the dramatic difference in frequency 
between relatively common and generally minor cervical spine injuries 
(such as whiplash) caused by forces acting on a seat occupant that can 
occur even in low-speed rear impacts and severe injuries, which are 
rare. Studies suggest that no more than 1% of rear impacts cause any 
type of serious or higher severity injury,\12\ which are mostly 
associated with impacts with vehicle structures, not other 
occupants.13 14 In contrast, cervical spine injuries, such 
as whiplash, are highly common injuries in rear impacts and occur at 
many different speeds, including at low speed, with some estimates of 
over 100,000 injuries annually in the United States. Additionally, 
despite decades of industry and agency research into whiplash, the 
understanding of the biological mechanisms that cause these injuries 
remain limited. This has restricted NHTSA's ability to develop 
objective updated performance standards for seat backs, such as updated 
strength requirements or a comprehensive dynamic test for rear impact 
protection. In particular, factors like test speed and what metrics of 
seat back and head restraint performance to test (i.e., strength only 
vs. anthropomorphic test dummy injury metrics) remain unclear. These 
and other related issues present a challenge to updating FMVSS No. 207 
in a manner that is objective, practicable, and meets the need for 
safety.
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    \12\ The severity of injury is ranked in accordance with the 
Abbreviated Injury Scale (AIS). An AIS level 3 injury is a serious 
injury, level 4 a severe injury, and levels 5 and 6 are critical and 
fatal injuries, respectively. www.aaam.org.
    \13\ Prasad, Priya, et al. ``Relationships between passenger car 
seat back strength and occupant injury severity in rear end 
collisions: Field and laboratory studies.'' SAE transactions (1997): 
3935-3967.
    \14\ Parenteau, Chantal S., and David C. Viano. ``Serious head, 
neck and spine injuries in rear impacts: frequency and sources.'' 
IRC-21-10, IRCOBI Conference. 2021.
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    This ANPRM is part of NHTSA's ongoing effort to meet this 
challenge. Here, we detail a unified approach to occupant protection in 
rear impacts. Although IIJA mentions only FMVSS No. 207, NHTSA is 
considering integrating FMVSS Nos. 207 and 202a because of the clear 
connection between head rests and seat backs. An integrated approach 
would enable NHTSA to comprehensively evaluate the performance of the 
seating system for rear impact protection and better balance 
considerations relevant to both high speed (severe injuries) and low-
speed (whiplash injury prevention) impacts. As part of this approach, 
NHTSA is considering a quasi-static test or a dynamic test requirement 
with at least two (low and high) impact severity ranges. This ANPRM 
discusses many considerations associated with each approach and seeks 
comment on them, including choice of anthropomorphic test device (ATD), 
performance criteria (such as ATD metrics), test severities, and crash 
pulse delivery methods.
    This ANPRM has four main areas of focus. In section II, NHTSA 
details the safety problem in rear impact occupant protection. In 
section III, NHTSA describes the regulatory and research history of 
seat backs, and in section IV, NHTSA summarizes a literature review in 
this area to provide context for the ANPRM.\15\ In section V, NHTSA 
discusses the Cantor, Saczalski, and CAS petitions. Finally, in section 
VI, NHTSA describes the unified approach with regard to FMVSS No. 207 
and FMVSS No. 202a, and in section VII, NHTSA describes its research 
efforts in this area and the knowledge gaps that may need to be filled 
prior to implementing this unified approach. Throughout the document, 
we seek comment on a variety of topics to inform a determination about 
what upgrade, if any, to FMVSS No. 207 (and FMVSS No. 202a) can meet 
the requirements of the Safety Act with the aim of improving occupant 
protection in rear impact collisions.
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    \15\ The research in the public domain on the area of seat back 
strength is extensive, and this document does not attempt to fully 
synthesize it.
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II. Occupant and Seat Back Dynamics and Field Data on Rear Impact 
Crashes

    Controlled interaction of the occupant with the seat back is the 
primary countermeasure to injury in motor vehicle rear collisions. In 
these crashes, the seat back supports the occupant during sudden 
forward acceleration, when a range of injury risks may be generated. 
Because it is necessary to provide a broad range of injury protections, 
the rear impact protection issue has been framed as both a balance and 
competition between high and low-severity protection measures. To 
introduce the issue, this section begins with a brief discussion of 
rear impact seat back dynamics and follows with a survey of field data 
regarding rear impacts.
    In front row seats, the seat back frame is typically connected to 
the lower seat structure, or pan, by a mechanical joint. When a seat 
back is subjected to an inertial load from the occupant during a rear 
collision, the seat back frame rotates and bends rearward around this 
joint. When asymmetric loading on the seat back occurs, this dynamic 
can result in twisting of the seat back around its longitudinal axis. 
The force acting on the seat back is proportional to the occupant's 
mass and forward acceleration. As the seat back rotates rearward, the 
force applied to the seat back becomes less perpendicular to the seat 
back plane as the applied force is further defined by transverse forces 
made up of seat back-occupant friction and pocketing,\16\ seat belt 
restraints, and other factors that maintain occupant seat 
retention.\17\ These actions have long been understood to absorb 
energy, reduce forces acting on the seat occupant, and disperse 
acceleration of

[[Page 58001]]

the occupant over time.18 19 When the force applied to the 
seat back exceeds the material's elastic limit, it begins to deform in 
a way that permanently bends the seat (plastic deformation). For some 
rear impacts, this deformation may exceed the seat structure's ability 
to substantially oppose the applied force, resulting in seat back 
failure due to significant material bending or fracture, at which point 
the seat back is said to fail. At the point of seat back failure or 
significant seat back deformation, seat occupants in rearward seat rows 
may be exposed to injury risk due to contact with the front seat back 
or front occupants. Paradoxically, the restraining force applied by the 
front seat on its occupant can lead to injury, just as a seat belt can 
injure an occupant in a frontal crash. The following sub-section 
examines field data to further lay out the current understanding of the 
risks to vehicle occupants in rear impacts. Later sections will provide 
additional discussion on the literature regarding rear impact injuries 
and protection. The literature outlines a continued debate around how 
best to protect occupants, the uncertain understanding of how certain 
injuries occur in rear impacts, and varied approaches and developments 
in technology for rear impact protection.
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    \16\ Pocketing refers to displacement of the occupant's torso 
into the relatively pliable interior of a seat back.
    \17\ Seat retention refers to the occupant restraint system's 
ability to keep the occupant coupled to the seat.
    \18\ Anderson JO. Dynamics of Occupants in Automotive Accidents 
Involving Rear Impacts. Warren, MI: Research Laboratories General 
Motors Corporation; 1961. Report No. R-34-1295.
    \19\ Severy DM, Mathewson J, Bechtol O. Controlled automobile 
rear-end collisions and investigation of related engineering and 
medical phenomena. Can Serv Med J. 1955;11:727-759.
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A. FARS and CRSS Data Analysis

    In general, rear collisions result in fewer fatalities and serious 
injuries when compared to other impact directions. Table II.1 shows 
overall crash statistics for the sum of light vehicles (passenger cars 
and light trucks) in year 2020 organized by impact directions and 
injury severities. NHTSA compiled this data set in the 2020 Traffic 
Safety Facts from FARS (Fatality Analysis Reporting System) and CRSS 
(Crash Report Sampling System).\20\ We note that the data include all 
vehicle rows. The data show that rear impacted light vehicles accounted 
for 24.1% of crashed light vehicles and 21.8% of vehicles with injured 
occupants, but only 7.2% of vehicles with fatalities in 2020.
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    \20\ National Center for Statistics and Analysis. (2022, 
October). Traffic Safety Facts 2020: A compilation of motor vehicle 
crash data (Report No. DOT HS 813 375). National Highway Traffic 
Safety Administration.

        Table II.1--Passenger Cars and Light Trucks Involved in Crashes, by Initial Point of Impact, Crash Severity, and Crash Type for Year 2020
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                                                                                              Crash severity
                                                 -------------------------------------------------------------------------------------------------------
      Crash type by initial point of impact                 Fatal                    Injury             Property damage only              Total
                                                 -------------------------------------------------------------------------------------------------------
                                                     Number      Percent       Number      Percent       Number      Percent       Number      Percent
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Single-Vehicle Crashes:
    Front.......................................       10,883         67.9      358,800         77.1      791,913         73.1    1,161,597         74.2
    Left Side...................................          890          5.6       21,960          4.7       54,317          5.0       77,167          4.9
    Right Side..................................          886          5.5       33,795          7.3       85,283          7.9      119,965          7.7
    Rear........................................          222          1.4       16,334          3.5       84,915          7.8      101,473          6.5
    Noncollision................................        1,714         10.7       27,237          5.9       40,898          3.8       69,849          4.5
    Other/Unknown...............................        1,430          8.9        7,157          1.5       25,991          2.4       34,580          2.2
                                                 -------------------------------------------------------------------------------------------------------
        Total...................................       16,025        100.0      465,285        100.0    1,083,319        100.0    1,564,629        100.0
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Multiple-Vehicle Crashes:
    Front.......................................       15,987         62.9    1,183,348         54.3    2,354,919         49.3    3,554,254         50.9
    Left Side...................................        3,221         12.7      224,185         10.3      522,635         10.9      750,041         10.7
    Right Side..................................        2,649         10.4      206,256          9.5      486,970         10.2      695,875         10.0
    Rear........................................        2,772         10.9      561,310         25.8    1,395,634         29.2    1,959,717         28.1
    Noncollision................................           76          0.3          702          0.0        2,474          0.1        3,253          0.0
    Other/Unknown...............................          704          2.8        2,787          0.1       17,515          0.4       21,007          0.3
                                                 -------------------------------------------------------------------------------------------------------
        Total...................................       25,409        100.0    2,178,589        100.0    4,780,149        100.0    6,984,146        100.0
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All Crashes:
    Front.......................................       26,870         64.9    1,542,149         58.3    3,146,832         53.7    4,715,850         55.2
    Left Side...................................        4,111          9.9      246,145          9.3      576,953          9.8      827,209          9.7
    Right Side..................................        3,535          8.5      240,051          9.1      572,254          9.8      815,839          9.5
    Rear........................................        2,994          7.2      577,646         21.8    1,480,551         25.3    2,061,189         24.1
    Noncollision................................        1,790          4.3       27,939          1.1       43,372          0.7       73,101          0.9
    Other/Unknown...............................        2,134          5.2        9,945          0.4       43,507          0.7       55,586          0.7
                                                 -------------------------------------------------------------------------------------------------------
        Total...................................       41,434        100.0    2,643,874        100.0    5,863,467        100.0    8,548,775        100.0
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    Of the over 2 million rear impacted light vehicles in 2020, only 
0.15% (2994/2,061,189) involved fatalities, as compared with 0.57% 
(26,870/4,715,850) of the 4.7 million front impacted light vehicles and 
0.47% (7646/1,643,048) of the 1.6 million side impacted light vehicles 
involved fatalities; a fatal rear collision is typically associated 
with a high [Delta]V \21\ collision.\22\ However, the injury rate in 
light vehicles that underwent a rear collision in 2020 is comparable to 
other crash directions, as 30% of rear impacted light vehicles involved 
injury, while 33% of frontal and 30% of side impacted light vehicles 
involved injury.
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    \21\ [Delta]V is defined as the maximum change in velocity of 
the struck vehicle after impact.
    \22\ Wang, J.-S. (2022, May). MAIS(05/08) injury probability 
curves as functions of [Delta]V (Report No. DOT HS 813 219) National 
Highway Traffic Safety Administration.
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    The count of occupant injury and fatality for different collision 
directions is classified by vehicle type for year 2020 in table II.2 
Traffic Safety Facts from FARS and CRSS. Restricting the discussion to 
light vehicles (passenger cars and light trucks), 6.1% of passenger car 
occupants and 4.6% of light truck occupants killed were due to rear

[[Page 58002]]

impacts. The combined light vehicle total was 5.4%. In contrast to the 
light vehicle fatality rate, the percentage of fatalities in rear 
impacted large trucks was only 2.9%. This would be consistent with the 
expectation that rear impact [Delta]V for large trucks would be on 
average smaller than for light vehicles.\23\
---------------------------------------------------------------------------

    \23\ [Delta]V is inversely proportional to the struck vehicle 
weight. Large trucks (including single-unit trucks and truck 
tractors) have a gross vehicle weight rating (GVWR) greater than 
10,000 pounds. Passenger cars and light trucks (including pickups, 
vans, and utility vehicles) have a GVWR not greater than 10,000 
pounds.

                       Table II.2--Vehicle Occupants Killed and Injured, by Initial Point of Impact and Vehicle Type for Year 2020
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                               Vehicle type
                                                --------------------------------------------------------------------------------------------------------
    Injury severity/initial point of impact       Passenger      Light        Large                     Other/
                                                     cars        trucks       trucks       Buses       unknown      Subtotal    Motorcycles     Total
--------------------------------------------------------------------------------------------------------------------------------------------------------
Occupants Killed:
    Front......................................        7,724        5,997          523            6          273       14,523         3,444       17,967
    Left Side..................................        1,849        1,129           35            1           53        3,067           300        3,367
    Right Side.................................        1,633          840           50            0           52        2,575           259        2,834
    Rear.......................................          822          474           24            1           70        1,391           242        1,633
    Other......................................          160          106           16            2           12          296            32          328
    Noncollision...............................          581        1,309          146            2          280        2,318           858        3,176
    Unknown....................................          703          497           37            4          125        1,366           444        1,810
                                                --------------------------------------------------------------------------------------------------------
        Total..................................       13,472       10,352          831           16          865       25,536         5,579       31,115
--------------------------------------------------------------------------------------------------------------------------------------------------------
Occupants Injured:
    Front......................................      696,221      440,711       21,175        1,958        3,023    1,163,087        41,952    1,205,039
    Left Side..................................      121,449       74,875        4,058        2,623          596      203,600         6,623      210,222
    Right Side.................................      109,313       77,510        4,429          920          447      192,620         5,863      198,483
    Rear.......................................      273,123      194,857        9,136        1,096          698      478,909         4,765      483,675
    Other......................................        5,600        3,584        1,228            0           38       10,451           289       10,740
    Noncollision...............................       15,248       21,698        4,895            1        2,012       43,854        23,010       66,864
    Unknown....................................          381          274           13           23           34          725            26          751
                                                --------------------------------------------------------------------------------------------------------
        Total..................................    1,221,335      813,509       44,934        6,620        6,849    2,093,246        82,528    2,175,774
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Further, according to the 2020 Traffic Safety Facts, 22.3% of 
passenger vehicle injuries occurred in rear impacts (light trucks = 
24.0%, heavy trucks = 20.3%). For each vehicle type, the proportion of 
fatalities for rear impacts is significantly lower than the 
corresponding proportion of injuries for rear impacts, compared to 
other initial impact directions. The rear impact proportion of 
fatalities in light trucks and heavy trucks is lower than in passenger 
cars, but the rear impact proportion of injuries in light trucks is 
slightly greater than in passenger cars and heavy trucks. The disparity 
in rear collision proportion of injuries for different vehicle types is 
discussed in the literature review below.

B. CISS Data Analysis

    NHTSA also examined the Crash Investigation Sampling System (CISS) 
data files for the years 2017-2020 to determine the number of rear 
impacts compared to other crash modes and determine the injury risk 
(number of injured occupants divided by the number of exposed 
occupants) of vehicle occupants in rear impacts. These data are limited 
because CISS currently reports only police reported, tow-away crashes, 
and, as will be explained later, most rear impacts are not tow-aways. 
The data were divided into different crash types: rollover, frontal, 
side, rear, other, and unknown. In addition, for rear impacts, the data 
were segmented by the change in velocity of the impacted vehicle 
([Delta]V). All data presented here are weighted to represent national 
estimates. The maximum abbreviated injury scale \24\ (MAIS) for each 
injured occupant is presented so that an occupant with multiple 
injuries is counted only once in the analysis. An occupant was counted 
as having a whiplash injury (MAIS 1 neck injury) even if they had other 
AIS 1 injuries. Crashes with fire have been excluded from the sample. 
If an occupant had a whiplash injury but also had a MAIS 2+ injury, 
they were not added to the whiplash injury count. As was the case for 
the FARS and CRSS data above, we have not restricted the data by 
seating row.
---------------------------------------------------------------------------

    \24\ The severity of injury is reported in CISS 2017-2020 using 
the 2015 Abbreviated Injury Scale, where AIS 1 are minor injuries, 
and the 2-6 categories are moderate, serious, severe, critical, and 
fatal injuries, respectively.
---------------------------------------------------------------------------

    The total annualized number of involved individuals was estimated 
to be 4.5 million, including crash types categorized as ``unknown'' and 
``other.'' Rear impact crashes accounted for only 373,237 or 8.3% of 
all tow-away crash involving individuals in the CISS database (Figure 
II.1). Only rollover crashes yield fewer occupants involved in tow-away 
crashes. Looking at the proportion of occupants with serious and higher 
severity injuries (MAIS 3-6) by crash type, we see that MAIS 3-6 are 
underrepresented in rear impacts (4.3% = 3,814/88,437) and 
overrepresented in rollover (19.7% = 17,415/88,437). By contrast 
whiplash injury is overrepresented in rear impacts (15.8% = 31,206/
197,060) as compared to the number of towed rear impacts.

[[Page 58003]]

[GRAPHIC] [TIFF OMITTED] TP16JY24.006


[[Page 58004]]


    Figure II.2 and Figure II.3 show the risk of MAIS 3-6 and whiplash 
injury \25\ for each towed crash mode. The risk of MAIS 3-6 injury in 
rear impacts is 1.0% (= 3,814/373,237), which is about 60% of the next 
highest risk (1.7% for side). The whiplash injury risk in rear impacts 
is approximately 8.4% (= 31,206/373,237), which is about 1.5 times the 
next highest risk (5.7% for rollover). These whiplash injury rates do 
not consider non-towed crashes, where the majority of whiplash injuries 
are known to occur.\26\
---------------------------------------------------------------------------

    \25\ Risk of MAIS 3-6 injuries in a crash mode is equal to the 
number of occupants with MAIS 3-6 injuries in that crash mode 
divided the total number of occupants (injured and uninjured) in 
that crash mode. Similar computation is done to determine risk of 
whiplash injuries.
    \26\ Final Regulatory Impact Analysis for FMVSS No. 202 Head 
Restraints for Passenger Vehicles, Docket NHTSA-2004-19807.
[GRAPHIC] [TIFF OMITTED] TP16JY24.007


[[Page 58005]]


[GRAPHIC] [TIFF OMITTED] TP16JY24.008


[[Page 58006]]


    Figure II.4 shows the distribution of towed rear impacts by the 
change in velocity of the rear impacted vehicle. Most of the crashes 
are in the 11-20 kilometers per hour (km/h) (6.8-12.4 miles per hour 
(mph)) [Delta]V range. Table II.3 provides tabulated annual occupant 
injuries in rear collisions according to injury severity and [Delta]V. 
For occupants in a known [Delta]V rear impact crash, the majority of 
injuries are estimated to be no injury (MAIS 0) in all [Delta]V ranges. 
The most probable known [Delta]V range for injury of any type is the 
11-20 km/h (6.8-12.4 mph) category, which is consistent with this being 
the most common impact speed range. More than three-quarters of MAIS 3+ 
rear impact injuries occur above 31 km/h (19.3 mph). Figure II.5 gives 
the risk of MAIS 2 and MAIS 3+ injuries as a function of impact 
[Delta]V in towed rear crashes. The highest risk for MAIS 2 injuries is 
8.4% (= 891/10,630) for 51+ km/h (31.7+ mph) [Delta]V crashes. The 
highest risk for MAIS 3+ is 7.0% (= 1,572/22,425) for the 31-40 km/h 
(19.3-24.9 mph) [Delta]V range. Figure II.6 shows that for whiplash, 
the highest risk is 11.7% (= 2,624/22,425) for injury in towed crashes 
occurring in the 26-35 km/h (16.2-21.8 mph) range. The risk at 51+ km/h 
is similar at 11.1% (= 1,183/10,630) and at other speeds is between 
2.8% and 9.7%.
[GRAPHIC] [TIFF OMITTED] TP16JY24.009


                                Table II.4--Annual Rear Impact Injury by [Delta]V
                                                [2017-2020 CISS]
----------------------------------------------------------------------------------------------------------------
                                                               MAIS 1 no
          [Delta]V (km/h)              MAIS 0      Whiplash     whiplash      MAIS 2      MAIS 3-6      Total
----------------------------------------------------------------------------------------------------------------
Unknown...........................      101,022       12,637       13,950        4,495          789      132,893
0-10..............................       22,057          675          913           59            0       23,704
11-20.............................       88,352        7,680       15,469        2,793          474      114,769
21-30.............................       46,618        6,302       10,429        1,455          249       65,052
31-40.............................       13,085        2,624        4,157          988        1,572       22,425
41-50.............................        1,811          107        1,661           94           92        3,764
51+...............................        5,173        1,183        2,746          891          638       10,630
                                   -----------------------------------------------------------------------------
    Total Known [Delta]V..........      177,095       18,569       35,375        6,279        3,025      240,345
    Total.........................      278,117       31,206       49,325       10,775        3,813      373,237
----------------------------------------------------------------------------------------------------------------


[[Page 58007]]

[GRAPHIC] [TIFF OMITTED] TP16JY24.010

[GRAPHIC] [TIFF OMITTED] TP16JY24.011

    Figure II.6 provides the whiplash injury rates for towed crashes. 
CISS does not collect injury data for non-towed crashes. In 2004, using 
State data, the Final Regulatory Impact Analysis for the upgrade of 
FMVSS No. 202 found four times as many whiplash injuries in all crashes 
compared to those in tow-away crashes. NHTSA plans to update

[[Page 58008]]

this analysis to accurately represent the current whiplash injury risk. 
Older field data, however, are still useful to provide a sense of the 
very large proportion of whiplash injuries that occur at low speed.
    With historical data, we can attempt to generate estimates that 
include non-towed whiplash. Between 1982 and 1986, non-towed crash data 
were collected. Table II.5 shows the distribution of an approximation 
of whiplash injuries occurring in towed and non-towed impacts for the 
1982-86 National Automotive Sampling System (NASS) data. The greatest 
ratio of non-towed to towed whiplashes was 20 times for the 0-10 km/h 
(0-6.2 mph) [Delta]V range. The next highest ratio was for the 11-20 
km/h (6.8-12.4 mph) range at 8 times.\27\ As expected, this ratio drops 
significantly at higher speeds because there are fewer non-towed 
crashes at these speeds. If we use the ratio of NASS data for non-towed 
to towed crashes as a multiplier for the CISS towed whiplash injury 
estimates in each speed range to attempt to account for the non-towed 
whiplash injuries in the newer data set, the result is column four in 
table II.5. If we distribute proportionally the cases of whiplash 
injuries where the impact speed was unknown to the known cases, the 
result is given in the fifth column. In this column we see that more 
than three-quarters (125,221/161,623) of all whiplash injuries occur at 
impact [Delta]V less than 20 km/h (12.4 mph). For only towaway rear 
impacts (not shown graphically) this [Delta]V limit captures 45% 
(8,355/18,570) of whiplash injuries. The whiplash injury distribution 
is shown graphically in Figure II.7. This estimate is provided to give 
a general sense of how considering whiplash injury only in tow-away 
crashes significantly underestimates overall whiplash injury 
distribution, particularly for lower speed crashes. This estimate comes 
with a large degree of uncertainty because it is based on historical 
NASS data.
---------------------------------------------------------------------------

    \27\ We note that these ratios are approximations from a 
slightly different [Delta]V segmentation.

                  Table II.5--Adjustments to Whiplash Injuries To Account for Non-Towed Crashes
----------------------------------------------------------------------------------------------------------------
                                             Ratio total to     Towed whiplash      Compensated       Unknown
              [Delta]V (km/h)                 towed (82-86    injury (2017-2020      whiplash        [Delta]V
                                                 NASS)              CISS)             injury        distributed
----------------------------------------------------------------------------------------------------------------
Unknown...................................              5.1               12,637          64,553  ..............
0-10......................................             19.8                  675          13,339          22,210
11-20.....................................              8.1                7,680          61,868         103,011
21-30.....................................              2.8                6,302          17,550          29,220
31-40.....................................              1.1                2,624           2,768           4,609
41-50.....................................              1.0                  107             110             184
51+.......................................              1.0                1,183           1,183           1,972
                                           ---------------------------------------------------------------------
    Total Known [Delta]V..................  ...............               18,570          96,819  ..............
    Total.................................  ...............               31,207         161,372         161,372
----------------------------------------------------------------------------------------------------------------

                                                                                                  [GRAPHIC] [TIFF OMITTED] TP16JY24.012
                                                                                                  

[[Page 58009]]

C. Field Data Analyses From Relevant Literature

    In an earlier 1997 study of the National Automotive Sampling 
System-Crashworthiness Data System (NASS-CDS) across years 1980-1994, 
Prasad \28\ found that rear impact collisions accounted for 11% of all 
possible struck vehicle scenarios. The distribution of crashes 
indicated that 50% of all rear impacts occur at [Delta]Vs of 21 km/h 
(13 mph) or less, 86% occur at [Delta]Vs less than 32 km/h (20 mph) and 
94% occur at [Delta]Vs of 40 km/h (25 mph) or less. Furthermore, when 
examining the distribution of injuries, it was found that less than 1% 
of rear end collisions resulted in severe injury of AIS 3 or more.
---------------------------------------------------------------------------

    \28\ Prasad, Priya, et al. ``Relationships between passenger car 
seat back strength and occupant injury severity in rear end 
collisions: Field and laboratory studies.'' SAE transactions (1997): 
3935-3967.
---------------------------------------------------------------------------

    In another study, Parenteau \29\ examined 1999 to 2015 NASS-CDS 
crash data to investigate the risk for MAIS 3+ outcomes including 
fatalities in crashes involving vehicles from model year (MY) 2000 and 
later. The risk for severe injury was lowest in rear crashes. The 
authors found head trauma to be the most likely severe injury for 
frontal passengers in rear collisions, followed by thorax and spinal 
injuries. The severe injuries were mostly the result of contact with 
the windshield, head restraint, and B-pillar. Many of these severe 
injuries develop from a seat retention issue (such as not wearing a 
seat belt) in which the occupant decouples from the seating system. It 
is unclear to what extent seat strength and retention issues overlap. 
The most severe injuries were attributed to forward intrusion of rear 
components.
---------------------------------------------------------------------------

    \29\ Parenteau, Chantal S., and David C. Viano. ``Serious head, 
neck and spine injuries in rear impacts: frequency and sources.'' 
IRC-21-10, IRCOBI Conference. 2021.
---------------------------------------------------------------------------

    Most rear collisions lead to a relatively low [Delta]V of the 
struck vehicle and this contributes to moderating injury of the vehicle 
occupants. The characteristics of the struck vehicle affect the injury 
severity and fatality risk of the occupants. As discussed in the next 
section, the majority of reported rear collision injuries are cervical 
injuries with or without clear pathology, while a small percentage of 
rear collisions are associated with high [Delta]V and severe injuries.

III. Statutory and Regulatory Background

A. The Safety Act and the Infrastructure, Investment and Jobs Act

    Congress enacted the Safety Act for the purpose of ``reduc[ing] 
traffic accidents and deaths and injuries resulting from traffic 
accidents.'' \30\ To accomplish this, the Safety Act authorizes the 
Secretary of Transportation to promulgate FMVSSs as well as to engage 
in other activities such as research and development. The Secretary has 
delegated the authority for implementing the Safety Act to NHTSA.\31\ 
The Safety Act requires that FMVSSs ``be practicable, meet the need for 
motor vehicle safety, and be stated in objective terms.'' \32\ To meet 
the Safety Act's requirement that standards be ``practicable,'' NHTSA 
must consider several factors, including technological and economic 
feasibility.\33\
---------------------------------------------------------------------------

    \30\ 49 U.S.C. 30101.
    \31\ 49 CFR 1.94.
    \32\ 49 U.S.C. 30111(a). The Secretary must also (1) consider 
relevant available motor vehicle safety information; (2) consult 
with the agency established under the Act of August 20, 1958 (Pub. 
L. 85-684, 72 Stat. 635), and other appropriate State or interstate 
authorities (including legislative committees); (3) consider whether 
a proposed standard is reasonable, practicable, and appropriate for 
the particular type of motor vehicle or motor vehicle equipment for 
which it is prescribed; and (4) consider the extent to which the 
standard will carry out the purpose of the Safety Act to reduce 
traffic accidents and deaths and injuries resulting from traffic 
accidents. 49 U.S.C. 30111(b).
    \33\ See, e.g., Paccar, Inc. v. Nat'l Highway Traffic Safety 
Admin., 573 F.2d 632, 634 n.5 (`` `Practicable' is defined to 
require consideration of all relevant factors, including 
technological ability to achieve the goal of a particular standard 
as well as consideration of economic factors.'') (citations and 
quotations omitted). Technological feasibility considerations 
counsel against standards for which ``many technical problems have 
been identified and no consensus exists for their resolution . . .'' 
while economic feasibility considerations focus on whether the cost 
on industry to comply with the standard would be prohibitive. Simms 
v. Nat'l Highway Traffic Safety Admin., 45 F.3d 999, 1011 (6th Cir. 
1995); See, e.g., Nat'l Truck Equip. Ass'n v. Nat'l Highway Traffic 
Safety Admin., 919 F.2d 1148, 1153-54 (6th Cir. 1990).
---------------------------------------------------------------------------

    In IIJA, Congress required NHTSA to issue this ANPRM to update 
FMVSS No. 207. The statute further states that if the Secretary 
determines a final rule complies with the Safety Act, a rule shall be 
issued with a compliance date not later than 2 motor vehicle model 
years after the model year the rule goes into effect.\34\ Under this 
requirement, NHTSA is required to issue a final rule only if it meets 
the requirements of the Safety Act, namely that it is practicable, 
meets the need for safety, and is objective. In determining whether to 
proceed with the rulemaking, NHTSA must also consider all of the 
factors set forth in 49 U.S.C. 30111(b).
---------------------------------------------------------------------------

    \34\ IIJA, section 24204 (2021).
---------------------------------------------------------------------------

B. Regulatory History of FMVSS No. 207 and FMVSS No. 202, and 
Associated Research/Analyses

1. 1963--SAE Recommended Practice for Seats
    The basis of the current FMVSS No. 207 standard is a recommended 
practice established by SAE International on November 1, 1963: SAE 
J879--Passenger Car Front Seat and Seat Adjuster. SAE J879 established 
uniform test procedures and minimum performance requirements for motor 
vehicle seats and seat adjusters.
    J879 defined two test procedures. The first procedure, ``Simulated 
Occupant Loading,'' tested rearward seat back strength. It required a 
seat back to withstand a rearward moment of 480 Nm (4,250 in-lb) that 
was generated via a static load applied to the uppermost cross member 
of the seat back frame. However, this moment was calculated ``about the 
rear attachments of the seat frame to the seat adjusters.'' The July 1, 
1968, revision to J879, J879B--Motor Vehicle Seating Systems, modified 
the moment to 373 Nm (3,300 in-lb) measured about the H-point, and the 
direction of the force was specified to be perpendicular to the seat 
back frame angle. The other procedure, ``Simulated Inertial Loading,'' 
established a 20 g minimum strength requirement for horizontal inertial 
seat loadings, applied in both the forward and rearward direction. This 
specification was designed to ensure that seat anchorages were 
strengthened to the point where the seats would remain attached to the 
vehicle body structure (typically the floor), preventing their inertia 
from releasing them and creating a ram-like action within the passenger 
compartment. During these tests, the seat back is braced to the seat 
base to isolate the seat attachment to the vehicle.
2. 1967--Publication of FMVSS No. 207, Seating Systems
    In February 1967, FMVSS No. 207 was enacted, and it went into force 
beginning with MY 1969 passenger cars.\35\ It was later extended to 
multipurpose vehicles, trucks, and buses in 1972.\36\
---------------------------------------------------------------------------

    \35\ 32 FR 2415 (Feb. 3, 1967).
    \36\ 36 FR 22945 (Dec. 2, 1971).
---------------------------------------------------------------------------

    FMVSS No. 207 mostly mirrored the 1963 version of SAE J879. 
However, the minimum rearward moment requirement was set at 373 Nm 
(3,300

[[Page 58010]]

in-lb) as measured about the H-point.\37\ Additionally, provisions were 
added for seats that folded forward to allow access to rear seats and 
to assure that seats had a positive restraining device (latch) to 
prevent them from swinging forward during a frontal crash. This 
prevented adverse inertial forces by a flailing seat back to the back 
of an occupant as they pitched forward during a frontal collision. The 
additional requirement also helped protect unrestrained rear seat 
occupants during frontal crashes or a hard breaking event who might 
otherwise get thrown over a pitched-forward seat back and could suffer 
injuries due to head impacts with the windshield or dash panel.
---------------------------------------------------------------------------

    \37\ The rulemaking that established FMVSS No. 207 did not 
discuss why it set a rearward moment with a different reference 
point and value than recommended by the 1963 version of SAE J879. 
See 32 FR 2415.
---------------------------------------------------------------------------

    The new provision required the latch (and, hence, the seat back 
itself) to withstand a forward load of 20 times the weight of the seat 
back. The load was applied to the seat back at its center of gravity. 
There was a concurrent revision to SAE J879 in July 1968. SAE also 
changed the moment value and its reference point in J879 to be 
consistent with FMVSS No. 207. However, the SAE requirement applied the 
force generating the moment in a direction perpendicular to the seat 
back instead of horizontally (see Figure III.1). The result of this 
change was that a slightly higher force must be applied in FMVSS No. 
207 to achieve the same moment level.\38\ Since then, the requirements 
of FMVSS No. 207 and SAE J879B have not changed.
---------------------------------------------------------------------------

    \38\ The magnitude of the force increase is equal to the inverse 
of the cosine of the angle of the seat back from the vertical. So a 
seat back with a 25 deg angle would have a 1.1 (1/cos(25)) times 
greater load applied in FMVSS No. 207 than in SAE J879.
[GRAPHIC] [TIFF OMITTED] TP16JY24.013

3. 1968--Publication of FMVSS No. 202, ``Head Restraints''
    In 1968, NHTSA issued FMVSS No. 202, ``Head restraints,'' requiring 
head restraints on cars manufactured after January 1, 1969.\39\ The 
standard specified that the head restraint must sustain an 890 N (200 
lb-f) rearward load applied 65 mm (2.5 in) below the top of the head 
restraint, while deflecting less than four inches (102 mm) and without 
a seat back failure. The standard also specified that the top of the 
head restraint must be at least 700 mm (27.5 in) above the H-point as 
measured along the torso reference line of the J826 manikin.\40\ This 
effectively placed a 565 Nm (5,000 in-lb) moment minimum strength 
requirement on the seat back while also placing a lower bound on seat 
back stiffness because this moment must be achieved within a specified 
amount of deflection. Thus, between FMVSS Nos. 202 and 207, all 
requirements for seat back strength were set forth through static 
loads.
---------------------------------------------------------------------------

    \39\ 33 FR 2945 (Feb. 12, 1968).
    \40\ SAE J826-1995: Devices for Use in Defining and Measuring 
Vehicle Seating Accommodation; 49 CFR 571.10; 73 FR 58896 (Oct. 8, 
2008).
---------------------------------------------------------------------------

4. 1969--Report on Seat Safety Studies at ITTE
    Following the issuance of FMVSS No. 207, Derwyn Severy, a principal 
investigator at the Institute of Transportation and Traffic Engineering 
(ITTE) at UCLA, published a paper \41\ at the 13th Stapp Car Crash 
Conference advocating safer seat designs (``Stapp paper''). The ITTE 
had been conducting field investigations and crash tests throughout the 
1960s as they worked to develop design concepts for vehicle seats.
---------------------------------------------------------------------------

    \41\ Severy, Derwyn M.; Brink, Harrison M.; Baird, Jack D; 
Blaisdell, David M.; ``Safer Seat Designs,'' Proceedings of the 13th 
Stapp Car Crash Conference Society of Automotive Engineers; 
Warrendale, PA December 2-4, 1969; Boston, MA.
---------------------------------------------------------------------------

    The 1969 Stapp paper provided the basis for several seat design 
recommendations. Included were recommendations to increase the seat 
back strength requirement to 11,300 Nm (100,000 in-lb) and limit the 
seat back rotation to 10 degrees in a quasi-static test. According to 
Severy, this load level was consistent with collision-induced forces 
caused by the seat inertial forces augmented by a 50th percentile male 
occupant in a 30 g rear-end crash.
    In 1976, Severy published a follow-on paper on seat design.\42\ In 
it, he offered his observations on safety improvements in production 
seats brought about by the 1968 standard: ``that laboratory tests 
established that production seats from cars large and small, foreign 
and domestic, and from vehicles 30 years old to new, have seat back 
strengths remarkably alike and that substantially exceed the required 
FMVSS No. 207 criteria.'' Severy additionally stated that production 
seats were incapable of effectively resisting motorist inertial forces 
for any but light impact exposures without experiencing excessive yield 
and/or component separation.
---------------------------------------------------------------------------

    \42\ Severy, D.M., Blaisdell, D.M., and Kerkoff, J. F.; 
``Automotive Seat Design and Collision Performance,'' 1976 SAE 
Transactions, Sec. 4, Vol. 85.

---------------------------------------------------------------------------

[[Page 58011]]

5. 1974--Notice of Proposed Rulemaking (NPRM) To Revise FMVSS No. 207
    In February 1974, Carl Nash of the Public Interest Research Group 
petitioned NHTSA to implement a dynamic requirement for seat backs. He 
asked NHTSA to add a rear impact test into FMVSS No. 208, ``Occupant 
crash protection,'' with acceptance criteria based on head rotation of 
a seated crash test dummy. Nash also called on NHTSA to consolidate 
FMVSS No. 202 with FMVSS No. 207 because of the close relationship 
between head restraints and seats in mitigating injuries in rear 
impacts.
    In March 1974, NHTSA published an NPRM that included proposed seat 
back requirements that essentially mirrored Nash's request.\43\ 
However, instead of amending FMVSS No. 208, NHTSA proposed to add the 
dynamic barrier test to a new, revised version of FMVSS No. 207. The 
test was to be conducted using the same moving barrier apparatus as 
that of the FMVSS No. 301 rear impact test for fuel system integrity, 
which had been proposed a year earlier.\44\ Although a seated dummy was 
specified, NHTSA did not propose any requirements based on dummy head 
rotation as requested by Nash. Instead, NHTSA proposed a maximum seat 
back rotation of 45 degrees. The proposal also integrated the 
requirements of FMVSS No. 202 into a single, consolidated standard.
---------------------------------------------------------------------------

    \43\ See, 39 FR 10268 (Mar. 19, 1974).
    \44\ See 38 FR 22417 (Aug. 20, 1973).
---------------------------------------------------------------------------

    To support a decision for a final rule, NHTSA contracted with the 
University of New Mexico to conduct rear impact tests. Sled tests were 
run on yielding vs. rigid seat backs using post-mortem human subjects 
(PMHS).\45\ At the time, NHTSA was concurrently investigating whether 
to revise FMVSS No. 202 to better mitigate the effects of whiplash. In 
consideration of this, rigid and yielding seats were tested with and 
without a head restraint. Sled tests were run by simulating a crash in 
which a stationary vehicle is struck from the rear by another vehicle 
having the same mass and travelling at a speed of 51 km/h (32 mph). The 
investigators observed that with no head restraint, rigid seats 
produced higher whiplash effects than yielding seats in low-speed rear 
impacts. Also, ramping was exacerbated in rigid seats with no head 
restraint. Thus, the results were deemed to be inconclusive as to 
whether yielding seats or rigid seats reduced the risk of injury. In 
addition to the work at the University of New Mexico, other basic 
research was being conducted on the more general topic of human injury 
tolerance to rearward forces and the biofidelity of the neck response 
of test dummies in rear impacts.46 47 It is noteworthy that 
NHTSA commissions another study in 1974 on the safety of occupants of 
large school buses (school buses with gross vehicle weight rating 
(GVWR) greater than 4,536 kilogram (kg) (10,000 pounds (lb))) prior to 
issuance of FMVSS No. 222.\48\ Following this study, NHTSA developed 
the concept of seating compartmentalization for school buses, which led 
to the following conclusion regarding the seating system: ``The seats 
and restraining barriers must be strong enough to maintain their 
integrity in a crash yet flexible enough to be capable of deflecting in 
a manner which absorbs the energy of the occupant.'' \49\ At least in 
the context of larger school buses, NHTSA found there was a benefit to 
yielding seats that maintain structural integrity in order to maintain 
occupant compartmentalization when occupants were not protected by seat 
belts. Based on this conclusion, NHTSA developed a force-deflection 
requirement for the forward and rearward directions for large school 
bus seat backs.\50\ The rearward requirement protects occupants in a 
rear collision, analogous to the rear impact issue discussed in this 
document.\51\
---------------------------------------------------------------------------

    \45\ Hu, Anthony S., Stewart P. Bean, and Roger M. Zimmerman. 
Response of belted dummy and cadaver to rear impact. No. 770929. SAE 
Technical Paper, 1977.
    \46\ Ewing, Channing L., et al. ``Effect of duration, rate of 
onset and peak sled acceleration on the dynamic response of the 
human head and neck.'' Proceedings: Stapp Car Crash Conference. Vol. 
20. Society of Automotive Engineers SAE, 1976.
    \47\ Muzzy, W. H. I., and Leonard Lustick. ``Comparison of 
kinematic parameters between hybrid II head and neck system with 
human volunteers for minus-Gx acceleration profiles.'' Proceedings: 
Stapp Car Crash Conference. Vol. 20. Society of Automotive Engineers 
SAE, 1976.
    \48\ 39 FR 27584 (July 30, 1974).
    \49\ 72 FR 65509 (Nov. 21, 2007).
    \50\ 49 CFR 571.222--Standard No. 222; School bus passenger 
seating and crash protection.
    \51\ A rear impact into a large school bus is a much less severe 
impact environment for the occupants of the bus than that of 
occupants of a light vehicle experiencing an equivalent rear impact.
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6. 1978--NHTSA Publishes a Request for Comment on Rulemaking Priorities
    On March 16, 1978, NHTSA published a Request for Comments on the 
agency's plan to prioritize ongoing rulemaking efforts.\52\ In 
establishing priorities for the plan, NHTSA stated that limited 
resources needed to be focused on rules with the largest safety 
benefits. It identified the 1974 proposal to require stiffer seats as 
one of several open rulemakings with low priority and proposed to 
terminate it. In 1979, when the plan was issued, the 1974 proposal was 
terminated.\53\ No public comments were received in response to the 
request for comments.
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    \52\ 43 FR 11100 (June 7, 1978).
    \53\ 44 FR 24591 (Apr. 26, 1979), ``Five Year Plan for Motor 
Vehicle and Fuel Economy Rulemaking''.
---------------------------------------------------------------------------

    Over the next several years, NHTSA continued to investigate the 
safety of occupants in rear impacts. Beginning in 1979, NHTSA conducted 
over 30 full-scale rear-impact crash tests on vehicles with 
instrumented dummies seated in the front seats. The FMVSS No. 301 
barrier was driven into the stationary vehicles at speeds ranging from 
48-56 km/h (30 to 35 mph). These rear impact crash tests are catalogued 
online.\54\
---------------------------------------------------------------------------

    \54\ https://www.nhtsa.gov/research-data/research-testing-databases#/vehicle/.
---------------------------------------------------------------------------

7. 1989--NHTSA Receives Petitions for Rulemaking on Revisions to FMVSS 
No. 207
    In 1989, Kenneth J. Saczalski and Alan Cantor submitted their first 
petitions for rulemaking on this subject to NHTSA.55 56 
Saczalski sought an increase in the seat back moment requirement in 
FMVSS No. 207 from 373 Nm (3,300 in-lb) to 6,330 Nm (56,000 in-lb),a 
factor of 17 increase. The aim was to reduce the incidence of injuries 
due to ramping and ejection in rear-end crashes. On July 24, 1989, 
NHTSA notified Saczalski that his petition was granted.
---------------------------------------------------------------------------

    \55\ Docket 89-20-No.1-001 or Docket NHTSA-1996-1817-0002. Both 
petitions have significant overlap to the 2014 Saczalski and 2015 
Cantor petitions discussed in this document.
    \56\ The previous NHTSA Seat Dockets, 89-20 Notices 1-3, are now 
available on the Docket Management System (DMS) at NHTSA-1998-1817, 
-4047 and -4064, respectively.
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    Cantor's 1989 petition asked NHTSA to amend FMVSS No. 207 to 
eliminate occupant ramping during a rear impact. Cantor did not provide 
a standardized test procedure to measure and assess ramping, nor did he 
describe a practicable countermeasure that could prevent ramping. 
Nonetheless, on February 28, 1990, NHTSA notified Cantor that his 
petition was granted.
    After granting these petitions, NHTSA published another request for 
comments (1989 RFC) on the need for amending the seat back performance 
requirement in FMVSS No. 207 and opened a docket to receive comments on 
the petitions and pertinent issues.\57\ In his comments submitted to 
this docket, Saczalski provided additional recommendations.\58\ He 
asked NHTSA

[[Page 58012]]

to also include a dynamic rear impact crash test using the FMVSS No. 
301 barrier and a 95th percentile male dummy in the seat.
---------------------------------------------------------------------------

    \57\ 54 FR 40897 (Oct. 4, 1989). Originally NHTSA Docket 89-20-
No. 1, and later transferred to Docket NHTSA-1996-1817.
    \58\ Docket NHTSA-1996-1817-0002.
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    Most comments from the automotive industry on the 1989 Saczalski 
and Cantor petitions opposed any new seat back stiffness requirements. 
They argued that real-world crash data did not indicate that a safety-
related problem existed. General Motors, for example, cited its own 
field data to conclude that any benefits associated with seat standard 
changes for rear impact protection were very limited.\59\ Ford cited a 
study of real-world crashes to conclude that a safety need did not 
exist.\60\ The authors of that analysis had also reviewed test data 
from prior studies (including those of Severy, et al). They concluded 
that rigid seat backs would probably exacerbate injuries because 
yielding seats absorb energy safely as they deform, thus reducing 
injurious forces borne by the occupant, including whiplash-causing 
forces. Occupant rebound from a rear impact and a subsequent hard 
thrust forward was also cited as a negative effect of rigid seats. 
Furthermore, a follow-up study by two of the same authors concluded 
that ramping is more likely to occur in a rigid seat regardless of 
whether a seat belt is used or a head restraint is in place.\61\ On the 
other hand, Mercedes-Benz supported an upgrade to FMVSS No. 207.\62\ It 
noted that seats in Mercedes vehicles were specifically designed to 
reduce the danger to front and rear occupants during rear impacts as a 
result of excessive rearward seat back deformation and the resultant 
interaction between occupants.
---------------------------------------------------------------------------

    \59\ Docket NHTSA-1996-1817-0010.
    \60\ Docket NHTSA-1996-1817-0004.
    \61\ James, M.B., Strother, C.E., Warner, C.Y., Decker, R.L., & 
Perl, T.R. (1991). Occupant protection in rear-end collisions: I. 
Safety priorities and seat belt effectiveness. SAE transactions, 
2019-2027.
    \62\ Docket NHTSA-1996-1817-0015.
---------------------------------------------------------------------------

    At the time, NHTSA commissioned a study on injury incidence to 
support a rulemaking decision.\63\ This analyzed the problem using NASS 
real-world crash data. The study confirmed that seat back yield in 
severe rear crashes does occur.\64\ Severe crashes were found to be 
infrequent, however, amounting to approximately 5% of all rear impacts. 
The study also showed that impacts with components in the rear seat 
compartment and ejections are a relatively small portion of the 
injuries. Injuries due to occupant impacts to components in the rear 
seat compartment accounted for 2.8% (unrestrained occupant) and 0.1% 
(restrained occupant) of the most severe injury to front seated 
occupants in rear impacts, and only 3.2% of all harm to unrestrained 
occupants in rear impacts involved occupant ejection.
---------------------------------------------------------------------------

    \63\ ``Current Issues of Occupant Protection in Car Rear 
Impacts,'' February 1990, Data Link, Inc., NHTSA Docket 89-20-No. 1-
21 or Docket Management System NHTSA-1996-1817-22.
    \64\ This study considered severe crashes as those with a 
vehicle change in velocity greater than 15 mph, CDC extent of damage 
(exterior vehicle damage) greater than 3, and at least one occupant 
with a maximum AIS of 3 or greater or with hospitalization or 
fatality.
---------------------------------------------------------------------------

    The study also concluded that current seat designs provided 
reasonable safety in rear-end crashes, and that seat belts are 
effective in reducing injuries. The report suggested that new head 
restraint designs offered the best possibility to mitigate the largest 
portion of injuries in rear-end crashes.
    Additionally, Transport Canada submitted a report to the docket of 
23 case studies of real-world rear impacts, all of which involved 
vehicles that experienced seat back failures, and 11 of which resulted 
in occupant ejections.\65\ Of the cases involving a rear seat 
passenger, four of the five rear passengers sustained injuries 
attributed to seat back failure of the front seat.
---------------------------------------------------------------------------

    \65\ NHTSA Docket 89-20-No. 1-018 or Docket Management System 
NHTSA-1996-1817-019.
---------------------------------------------------------------------------

    NHTSA provided a summation of the comments and reports in a 1992 
summary report.\66\ This document was placed in the docket for the 
safety plan discussed below. The report concluded that improving 
seating system performance may be more complex than simply increasing 
the strength of the seat back, and that a proper balance in seat back 
strength and compatible interaction with head restraints and seat belts 
must be obtained to optimize injury mitigation.
---------------------------------------------------------------------------

    \66\ NHTSA Docket 89-20-No. 3-001 or Docket Management System 
NHTSA-1998-4064-001.
---------------------------------------------------------------------------

8. 1992-2000 NHTSA Publishes a Request for Comment on Possible 
Revisions to FMVSS No. 207, Grants Two Petitions and Conducts Research
    In November 1992, the agency published another Request for Comment 
on more recent research findings and a proposed plan to address seat 
back performance.\67\ At that time, the agency had refrained from 
upgrading FMVSS No. 207 until significant results from research were 
obtained, though the rulemaking action resulting from the 1989 petition 
grants was still open. The first document the agency placed in the 
docket was a report summarizing agency findings up to that point. The 
1992 report stated that four categories of performance issues need to 
be addressed as part of potential future changes to FMVSS No. 207.\68\ 
These four categories are:
---------------------------------------------------------------------------

    \67\ 57 FR 54958 (Nov. 23, 1992).
    \68\ ``Summary of Safety Issues Related to FMVSS No. 207,'' 
(1992), NHTSA-1998-4046-001.

    (1) Seating system integrity: the ability of the seat and its 
anchorage to the vehicle to withstand crash forces without failure.
    (2) Energy absorbing capability: the extent to which the seat 
and its attachment components absorb energy and the manner in which 
the seat and its attachment components release energy during 
rebound.
    (3) Compatibility of a seat and its head restraint: The concern 
in this category is that any change in seat back energy absorbing 
capability could exacerbate head or neck injuries if the geometry 
and energy absorbing capability of the head restraint is not also 
changed.
    (4) Seat belt restraint system: a seating system and its seat 
belt restraint system must complement each other to prevent injury.

    Over the ensuing 10-year period, the agency conducted extensive 
physical testing of seat backs, performed computer modeling of seated 
occupants in rear impacts, and conducted dynamic testing of 
instrumented test dummies in vehicle seats. At the same time, NHTSA 
also assessed how new requirements for head restraints could mitigate 
whiplash injury in lower-speed rear-end crashes. The details of those 
efforts are outlined in several NHTSA reports provided in docket folder 
NHTSA-1998-4064 (document numbers 24-27, 31).
    NHTSA also granted two more petitions related to seat back 
strength: King (March 1998) \69\ and Hogan (December 1998).\70\ King 
petitioned for a dynamic test using the FMVSS No. 301 rear impact test 
procedure. Hogan stated that conformance to the current regulation was 
being used in litigation as a defense for the performance of 
contemporary seat designs, and therefore asked NHTSA to ``suspend'' 
FMVSS No. 207 until such time that the standard could be improved.
---------------------------------------------------------------------------

    \69\ NHTSA-1998-4377-0001.
    \70\ NHTSA-1999-5482-0008.
---------------------------------------------------------------------------

    In comments posted in dockets NHTSA-1996-1817 \71\ and NHTSA-1998-
4064,\72\ most in the automobile industry argued that seat back 
deformation was protective to the occupant by absorbing some crash 
energy. However, there was recognition that better seat back 
performance requirements could improve occupant safety in rear impacts 
greater than 40 km/h (25 mph). Greater control of

[[Page 58013]]

occupant kinematics in severe rear crashes was thought to enhance 
occupant safety, even for belted occupants, by controlling rearward 
deflection of the seat back. Further comments presented by the 
Advocates for Highway and Auto Safety expressed concern about the harm 
caused by bodily impact with vehicle structures and noted the 
importance of negating excessive seat back rotation, ramping, and 
occupant rebound. One individual consultant described the consultant's 
opinion regarding the deficiency of FMVSS No. 207 and the impact that 
the standard may have had on automotive seat designs from that time. 
Another consulting firm expressed concern about the level of 
deformation that occurs due to the force applied to seat backs of that 
time in rear impacts and its effect on the effectiveness of the 
restraint systems in higher severity rear impacts.
---------------------------------------------------------------------------

    \71\ These were originally posted to NHTSA Docket 89-20-No 1, 
and subsequently transferred to Docket NHTSA-1996-1817.
    \72\ These were originally posted to NHTSA Docket 89-20-No 3, 
and subsequently transferred to Docket NHTSA-1998-4064.
---------------------------------------------------------------------------

    The comments and research at the time affirmed that the issues of 
seat back, head restraint, and belt retention were inextricably linked 
to overall occupant safety. For example, in studies such as the 1997 
Prasad,\73\ 1977 University of New Mexico study, and 1976 Severy study, 
the disbenefits of a rigid seat were particularly evident in seats with 
baseline head restraints.\74\ In the 1997 Prasad study for example, the 
authors found that stiffer seats led to higher neck and lumbar spine 
loads in rear impact tests. One complicating factor from this period is 
that most of the laboratory tests were performed with Hybrid II or 
Hybrid III 50th percentile male (HIII-50M) dummies, which are seated 
dummies designed based on human indices measured in frontal crashes. 
The torso and pelvis of these dummies do not articulate well in rear 
impacts, and such articulation is needed to faithfully exhibit ramping. 
While a larger size ATD would more fully exercise a seat back in a rear 
impact, the additional use of a smaller ATD with female-specific 
characteristics may have provided a more comprehensive assessment of 
occupant kinematics and injury risk for different seat designs in these 
earlier studies. Comments posted in the docket also emphasized the rear 
impact protection points NHTSA made in the 1992 study, in particular 
the need for energy absorption of the seat back, while also recognizing 
that performance requirements may enhance rear impact protection.
---------------------------------------------------------------------------

    \73\ See below in Review of Additional Literature, Occupant 
Dynamics, for an in-depth discussion of the findings.
    \74\ The term ``baseline'' indicates head restraints 
manufactured prior to the 2004 update of the head restraint 
standard. These provided much less protection than those mandated by 
today's Federal standard. 69 FR 74848 (Dec. 14, 2004).
---------------------------------------------------------------------------

9. 2004--NHTSA Issues Final Rule Upgrading FMVSS No. 202, Head 
Restraints
    NHTSA's research on rear impact crashes and head restraints led the 
agency in January 2001, to address the problem of whiplash injuries by 
proposing to upgrade the head restraint standard, FMVSS No. 202.\75\ At 
the time, the agency estimated that approximately 800,000 whiplash 
injuries occurred annually in all crash types, resulting in a total 
annual cost of $5.2 billion. Whiplashes in rear impacts were estimated 
to be about 270,000 annually.
---------------------------------------------------------------------------

    \75\ 66 FR 968 (Jan. 4, 2001).
---------------------------------------------------------------------------

    After considering public comments on the proposal, NHTSA published 
the final rule on December 14, 2004.\76\ It was estimated to reduce the 
number of whiplash injuries by about 17,000 per year. The revised 
standard imposed an increased head restraint height requirement such 
that all outboard front seat head restraints must be capable of 
adjusting to at least 800 mm (31.5 in) and not have an adjustment 
position below 750 mm (29.5 in). It also imposed a minimum backset \77\ 
measurement that required the head restraint to be closer to the back 
of a seated occupant's head. The updated standard maintained the 
requirement for the head restraint to withstand a 200 lb-f or 890 N 
rearward force applied 65 mm (2.5 in) below its top, when adjusted to 
its highest position, which must be at least 800 mm. Thus, this imposes 
an effective rearward strength requirement on seat backs of 654 Nm 
(5,790 in-lb), where 654 = 890*(0.8-0.065). This is a factor of 1.75 
greater than the rearward strength requirement of FMVSS No. 207.
---------------------------------------------------------------------------

    \76\ 69 FR 74848 (Dec. 14, 2004).
    \77\ Backset is defined as minimum horizontal distance between 
the rear of a representation of the head of a seated 50th percentile 
male occupant and the head restraint, as measured by the head 
restraint measurement device. 49 CFR 571.202(a).
---------------------------------------------------------------------------

10. 2004--NHTSA Terminates Rulemaking on FMVSS No. 207, Seating Systems
    By the time NHTSA finalized the head restraint regulation in 2004, 
it was clear to the agency that additional research and data analyses 
were needed to allow a fully informed decision on any change to the 
seat back strength requirement in FMVSS No. 207. A year earlier, 
researchers at Johns Hopkins University Applied Physics Laboratory 
completed a study commissioned by NHTSA, which strongly suggested that 
seat back stiffness plays a role in whiplash injury risk in low-speed 
rear impacts.\78\ The main finding was that the risk of whiplash injury 
cannot be related to a single design factor, such as head restraint 
height. The study concluded that altering the seat back design could 
have an effect on the occurrence of whiplash. Additional analyses were 
needed to assure that a NHTSA-imposed seat back requirement would not 
create a greater risk of whiplash. Since it was not clear when such 
analyses would be complete, on November 16, 2004, NHTSA terminated the 
FMVSS No. 207 rulemaking proceeding that had been open since 1989.\79\ 
NHTSA was unable to fully establish that a need for a stronger seat 
back existed, establish a definitive link between injury reductions and 
potential new regulatory seat back requirements, or show that new 
requirements under consideration would not exacerbate risk of neck 
injuries due to whiplash, roof contacts, or rebound. However, NHTSA did 
not make a finding that an FMVSS No. 207 amendment was not warranted. 
Instead, NHTSA stated that further study is needed to make a definitive 
determination of the relative merits of different potential rulemaking 
approaches and that research on seat back issues would continue.
---------------------------------------------------------------------------

    \78\ Kleinberger M, Voo LM, Merkle A, Bevan M, Chang S: The Role 
of Seatback and Head Restraint Design Parameters on Rear Impact 
Occupant Dynamics. Proceedings of 18th International Technical 
Conference on the Enhanced Safety of Vehicles, Paper #18ESV-000229, 
Nagoya, Japan, May 19-22, 2003.
    \79\ 69 FR 67068 (Nov. 16, 2004).
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11. Further Regulatory Changes Since 2004
    There have been two prominent regulatory changes regarding occupant 
safety in rear-end crashes that have been fully implemented since NHTSA 
terminated the rulemaking on FMVSS No. 207: a revision to FMVSS No. 
202, and a revision to FMVSS No. 301, the fuel system integrity 
standard. FMVSS No. 202 is the standard focused on neck injury 
protection in rear impacts. Regarding FMVSS No. 301, while the stated 
purpose of the standard is to reduce incidence of fire and fuel 
ingestion incidents, it utilizes a test procedure that represents a 
relatively severe rear impact in the field and has been recommended by 
petitioners as a viable basis for an upgrade to FMVSS No. 207. 
Additionally, some researchers have reported that vehicles compliant 
with the updated FMVSS No. 301 have shown significant reduction in 
fatality risk in rear impact.\80\ Therefore, as part

[[Page 58014]]

of our analysis of the need for new seat back strength requirements, 
NHTSA considers the effects that these changes have had on seat 
performance and occupant injury risk in moderate-to-severe rear-end 
crashes.
---------------------------------------------------------------------------

    \80\ Viano, David C., and Chantal S. Parenteau. ``Effectiveness 
of the revision to FMVSS 301: FARS and NASS-CDS analysis of 
fatalities and severe injuries in rear impacts.'' Accident Analysis 
& Prevention 89 (2016): 1-8.
---------------------------------------------------------------------------

(a) FMVSS No. 202a, ``Head Restraints''
    FMVSS No. 202a was issued in 2004 and applied an updated set of 
safety requirements for head restraints beginning with model year 
2010.\81\ Although the new requirements were not specifically intended 
to strengthen seat backs, the head restraint upgrade resulted in an 
increase in the minimum acceptable seat back strength.
---------------------------------------------------------------------------

    \81\ 49 CFR 571.202a. See also 69 FR 74848 (Dec. 14, 2004). Many 
requirements became effective on September 1, 2009, while others, in 
particular those regarding rear head restraints, came into effect 
the following year. Please review S2 of the standard for further 
details.
---------------------------------------------------------------------------

    FMVSS No. 202a requires a fully extended head restraint to 
withstand an 890 N (200 lb-f) rearward load. Although this load was not 
changed in FMVSS No. 202a, the minimum height of the head restraint was 
raised from 700 mm to 800 mm. Thus, the effective torque requirement on 
the seat back increased from about 565 Nm (5,000 in-lb) to 654 Nm 
(5,790 in-lb).\82\
---------------------------------------------------------------------------

    \82\ Agency testing of pre-FMVSS No. 202a seats showed seat back 
strength well in excess of 654 Nm, so there was no need for 
manufacturers to increase seat back strength to meet the new head 
restraint requirements of FMVSS No. 202a, see Docket document no. 
NHTSA-1998-4064-0026.
---------------------------------------------------------------------------

    FMVSS No. 202a also introduced a new optional dynamic test for head 
restraints. In the dynamic test, the entire vehicle is tested on a sled 
with a seated HIII-50M dummy and subjected to a 17.3 km/h (10.75 mph) 
rear impulse. The dummy's rearward head rotation with respect to its 
torso must be limited to 12 degrees for the dummy in all outboard 
designated seating positions. Though inertial forces of the occupant 
acting on the seat back in FMVSS No. 202a testing are much lower 
compared to those associated with an FMVSS No. 301 test pulse, FMVSS 
No. 202a's dynamic test may have potentially resulted in stronger seat 
back designs for those seats certified to this option because a stiffer 
seat back with an adequately positioned head restraint would capture 
the head motion before the limits are exceeded. Neither NHTSA nor, to 
our knowledge, the petitioners, however, have studied whether the 
upgrade to FMVSS No. 202a has resulted in injury reductions other than 
whiplash.
(b) Upgrade to FMVSS No. 301, Fuel System Integrity
    On November 13, 2000, NHTSA proposed a more stringent rear impact 
offset test using a lighter deformable barrier.\83\ A final rule was 
published on December 1, 2003, and the new requirements for the fuel 
systems were phased in during MYs 2007-2009.\84\ Although the fuel 
containment requirements remained the same as the previous version of 
FMVSS No. 301, the crash test was generally more rigorous for most 
passenger cars. Vehicles that passed the new rear impact requirements 
were found to provide protection against crashes in which the impact 
produced a 33 to 50 percent higher [Delta]V (which corresponds to 110 
percent more energy being dissipated in the crash) compared to the 
previous test.\85\
---------------------------------------------------------------------------

    \83\ 65 FR 67693 (Nov. 13, 2000).
    \84\ 68 FR 67068 (Dec. 1, 2003).
    \85\ Pai, Jia-Ern. ``Evaluation of FMVSS NO. 301, `Fuel System 
Integrity,' as upgraded in 2005 TO 2009.'' National Center for 
Statistics and Analysis, National Highway Traffic Safety 
Administration. Washington, DC (2014).
---------------------------------------------------------------------------

    In a post-regulatory assessment, NHTSA compared the structure of 
pre- and post-standard vehicles. NHTSA observed substantial structure 
upgrades in the newer vehicles, which may mitigate intrusion of vehicle 
structures into the rear seat occupant compartment. For example, in the 
2016 study, Viano and Parenteau found MY 2008 and onward FMVSS No. 301 
compliant vehicles to have a 27.1-32.8% reduction in fatality risk in 
rear impacts compared to 1996-2001 MY vehicles. Two considerations 
limit the conclusions that can be drawn from this data. First, injury 
risk was estimated irrespective of post-crash fire. Thus, some of the 
injury risk reduction could be a reduction in the incidence of fire. 
Second, the authors noted that the changes in rear structures occurred 
while front seats were transitioning to higher retention designs, which 
may contribute to the reduction in fatality risk.
(c) NCAP
    In 2007 NHTSA published a notice requesting comments on an agency 
report titled ``The New Car Assessment Program (NCAP) Suggested 
Approaches for Future Program Enhancements.'' \86\ With regard to rear 
impact protection, NHTSA proposed that it could provide consumers with 
basic information on rear crashes such as safe driving behavior, proper 
adjustment of head restraints, real-world safety data by vehicle 
classes, and links to the Insurance Institute of Highway Safety (IIHS) 
rear impact test results. The agency further proposed that a dynamic 
rear impact test, which addresses those injuries not covered by the 
agency's current standards, could be investigated and incorporated into 
the ratings program. Several organizations and manufacturers 
recommended that NHTSA evaluate the effectiveness, cost, and safety 
benefits of a rear impact test before incorporating such a test into 
NCAP. Industry comments suggested that NHTSA should also evaluate the 
effectiveness of the FMVSS No. 202a update and that incorporating rear 
impact safety into NCAP would be better directed toward areas not fully 
addressed by the current regulation. Commentors suggested that NHTSA 
should study whiplash-type injuries and countermeasures and encourage 
public education on the proper adjustment of the head restraint. NHTSA 
concluded that a dynamic test would not be premature at that time since 
such an option existed in FMVSS No. 202a. However, NHTSA noted that the 
test dummy used by IIHS is not used for testing FMVSS compliance, and 
some of the injury criteria used for the assessment had not been 
correlated with real-world injury. Ultimately, the agency did not 
incorporate rear impact protection information into the NCAP program.
---------------------------------------------------------------------------

    \86\ 72 FR 3473 (Jan. 25, 2007).
---------------------------------------------------------------------------

IV. Review of Additional Literature

    NHTSA, industrial, academic, and non-profit researchers have 
conducted significant research into the rear impact protection of seat 
backs and head restraints, and research is ongoing. Researchers have 
investigated occupant dynamics in rear impacts, development of safer 
seats for the occupant in rear impacts, and occupant injury mechanisms 
in rear impacts.

A. Occupant Dynamics

    Occupant dynamics and protection in rear collisions is a complex 
multivariable problem. The ideal safe seat for one occupant in a 
certain rear collision scenario may not be the ideal safe seat for 
another occupant or for a different scenario. For example, research 
suggests that females have a higher risk of whiplash injury compared to 
males and respond differently to a rear impact.87 88 89 90 
Additionally, other

[[Page 58015]]

occupant characteristics, such as weight, can play a significant role 
in rear impact injury risk, as shown in the NASS-CDS case number 2011-
49-57 noted by Viano and Parenteau.\91\ This case outlines a rear 
collision with an estimated [Delta]V between 35 and 39 km/h (21.7 and 
24.2 mph). The 141 kg (311 lb) driver of the rear impacted 2008 model 
passenger vehicle suffered critical head and neck injuries after 
decoupling from the rotated driver seat back and colliding with the 
rear seat back. The 68 kg (150 lb) right front passenger of the same 
struck vehicle, however, had no documented injury.\92\ The injury 
severity suffered by the driver in this case is rare in rear impacts. 
Viano and Parenteau found passengers with injuries of MAIS 4 or greater 
severity, including fatalities, represented 0.08% of passengers with 
injury in rear collisions in MY 2008 and newer vehicles. A quantitative 
description of seat back response is complicated by the potential 
sensitivity of response to a range of initial conditions and external 
factors including head posture,\93\ awareness,\94\ seat belt use and 
seat geometry including initial seat back recline angle,\95\ details of 
the crash pulse,96 97 and specific occupant characteristics 
such as weight distribution. The initial posture and location of the 
occupant is also thought to influence injury risk. Many occupants in 
rear collisions are believed to be out-of-position (e.g., seated off-
center), and out-of-position occupants are thought to have a higher 
probability of injury in rear impacts than symmetrically or normal-
positioned occupants.98 99 100
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    \87\ Berglund A, Alfredsson L, Jensen I, et al. Occupant- and 
crash-related factors associated with the risk of whiplash injury. 
Ann Epidemiol 2003;13:66-72.
    \88\ Carlsson, Anna. Addressing female whiplash injury 
protection-a step towards 50th percentile female rear impact 
occupant models. Chalmers Tekniska Hogskola (Sweden), 2012.
    \89\ Viano, David C. ``Seat influences on female neck responses 
in rear crashes: a reason why women have higher whiplash rates.'' 
Traffic injury prevention 4.3 (2003): 228-239.
    \90\ Linder, Astrid, and Mats Y. Svensson. ``Road safety: the 
average male as a norm in vehicle occupant crash safety 
assessment.'' Interdisciplinary Science Reviews 44.2 (2019): 140-
153.
    \91\ Viano, David C., and Chantal S. Parenteau. ``Effectiveness 
of the revision to FMVSS 301: FARS and NASS-CDS analysis of 
fatalities and severe injuries in rear impacts.'' Accident Analysis 
& Prevention 89 (2016): 1-8.
    \92\ Comparisons such as these should be made with care because 
the driver and passenger seat may not be structurally identical, 
with the driver seat sometimes having more and powered adjustments 
compared to the passenger seat.
    \93\ Lenard, James, Karthikeyan Ekambaram, and Andrew Morris. 
``Position and rotation of driver's head as risk factor for whiplash 
in rear impacts.'' J Ergonomics S 3.2 (2015).
    \94\ Siegmund, Gunter P., et al. ``Awareness affects the 
response of human subjects exposed to a single whiplash-like 
perturbation.'' Spine 28.7 (2003): 671-679.
    \95\ Kang, Yun-Seok, et al. ``Effects of seatback recline and 
belt restraint type on PMHS responses and injuries in rear-facing 
frontal impacts.'' SAE International journal of transportation 
safety 10.2 (2022): 09-10.
    \96\ Hynes, Loriann M., and James P. Dickey. ``The rate of 
change of acceleration: Implications to head kinematics during rear-
end impacts.'' Accident Analysis & Prevention 40.3 (2008): 1063-
1068.
    \97\ Siegmund, Gunter P., et al. ``The effect of collision pulse 
properties on seven proposed whiplash injury criteria.'' Accident 
Analysis & Prevention 37.2 (2005): 275-285.
    \98\ Strother, Charles E., Michael B. James, and John Jay 
Gordon. ``Response of out-of-position dummies in rear impact.'' SAE 
transactions (1994): 1501-1529.
    \99\ Benson, Brent R., et al. ``Effect of seat stiffness in out-
of-position occupant response in rear-end collisions.'' SAE 
transactions (1996): 1958-1971.
    \100\ Burnett, Roger A., Chantal S. Parenteau, and Samuel D. 
White. ``The effect of seatback deformation on out-of-position 
front-seat occupants in severe rear impacts.'' Traffic Injury 
Prevention (2022): 1-5.
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    Some research suggests that limiting seat back rotation can have 
detrimental effects, particularly regarding neck injuries. In the 1997 
Prasad study of real-world rear impacts, the authors concluded that a 
revision to severely limit seat back rotation would have detrimental 
effects. The study analyzed the 1980-94 NASS database to compare injury 
rates in pickup trucks with passenger vehicles in rear impacts. This 
allowed for comparison between yielding seat performance with the 
rotationally stiff seats of pickup trucks (stiffness is due to the 
small gap between seat and cab). A higher rate of occupant injury in 
rear collisions across all [Delta]Vs was observed in pickup trucks. The 
authors inferred that rotationally rigid seats could have an increased 
rate of injury in rear impacts. The 1997 Prasad study further analyzed 
a series of sled tests to investigate the relationship between seat 
stiffness and anthropomorphic test device (ATD) kinematics for rear 
impact [Delta]V of 16, 24, and 40 km/h (9.9, 14.9, and 24.9 mph). After 
assessing the range of sampled speeds and ATD measurements, Prasad 
hypothesized that (all else being equal) stiffening of the baseline 
1996 production seats can result in an overall increase in whiplash 
type injuries at low-to-moderate speeds and a greater potential for 
serious neck injury at higher speeds, in addition to other conclusions. 
This study, however, has limitations. Many of the pickups in the crash 
data analyzed may not have had head restraints because trucks were not 
required to have head restraints until MY 1993. Moreover, a 
rotationally rigid seat represents the extreme end of the debate around 
the seat strength set by FMVSS No. 207. While modern production seats 
are characterized by a seat strength many times the value set by FMVSS 
No. 207, these seats also display a degree of balance between high and 
low-speed rear impact protection and the characteristic of rearward 
rotation of the seat back.
    Other research suggests that optimizing seat back design, including 
stiffness, can reduce injury risks in rear impact. In a 1996 study, 
Svensson, et al.\101\ analyzed the influence of seat back properties on 
neck injury using the HIII ATD with a Rear Impact Dummy (RID)-neck in 
low-speed rear collision sled testing. The study found that it was 
possible to significantly reduce harmful head-neck motion of the ATD by 
optimizing the head-to-head restraint gap, seat back frame stiffness, 
and characteristics of the seat-back cushion.
---------------------------------------------------------------------------

    \101\ Svensson, Mats Y., et al. ``The influence of seat-back and 
head-restraint properties on the head-neck motion during rear-
impact.'' Accident Analysis & Prevention 28.2 (1996): 221-227.
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    A separate statistical analysis involving 20 years of the NASS 
database by Burnett \102\ found that front seat occupants are 
significantly more protected in rear collisions compared to other crash 
directions, even for the most severe rear impacts where major seat 
yielding and occupant decoupling from the seat can occur. The study 
also conducted quasi-static mechanical testing and rear impact sled 
tests of seven production seats to investigate the correlation between 
mechanical parameters and ATD kinematics. The study found no 
significant correlation between the seat strength and any of the 
recorded ATD metrics, while seat stiffness and an energy absorption 
parameter were nonlinearly correlated with ATD metrics.
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    \102\ Burnett, Roger, et al. ``The influence of seatback 
characteristics on cervical injury risk in severe rear impacts.'' 
Accident Analysis & Prevention 36.4 (2004): 591-601.
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B. Rear Impact Protection Technology

    This section discusses some seat designs intended to improve rear 
impact protection that have been incorporated over the years.
    In 1998, a set of design guidelines was published by Volvo Cars and 
Autoliv, Inc. for seats that emphasized the importance of controlling 
an occupants' absolute and relative head and torso kinematics 
throughout the rear impact process, to protect against neck and other 
injuries.\103\ The Volvo Cars' Whiplash Protection System (WHIPS) was 
introduced in 1998 and is built around these guidelines. In a 
significant rear collision, the first generation WHIPS seat back 
rotation point moves rearward and later transitions to rearward 
rotation. During seat back rotation, a mechanical linkage

[[Page 58016]]

irreversibly absorbs rotational energy, so there is less energy 
directed into the occupant and rebound is reduced. The seat back will 
then continue to rotate and deflect rearward as a typical production 
seat. According to data reported by Volvo, the first generation WHIPS 
seat reduced soft tissue neck injury risk by 21% to 47% as compared to 
prior seats.\104\
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    \103\ Lundell, Bjorn, et al. ``The WHIPS seat-a car seat for 
improved protection against neck injuries in rear-end impacts.'' 
Proc. 16th ESV Conference, Paper. Vol. 98. 1998.
    \104\ Jakobsson, Lotta, Irene Isaksson-Hellman, and Magdalena 
Lindman. ``WHIPS (Volvo cars' Whiplash Protection System)--the 
development and real-world performance.'' Traffic injury prevention 
9.6 (2008): 600-605.
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    Another technology for whiplash injury protection is active head 
restraints that was introduced by Saab in the late 1990s.\105\ These 
systems aim to reduce the head restraint contact time by actively 
shifting the head restraint forward in a rear impact through a 
mechanical linkage in the seat structure activated when the seat 
occupant moves rearward into the seat. Data acquired by the NCAP 
program for MY2023 show that 21 vehicle models representing 4 percent 
of vehicle sales are reported as having active head restraints or 
provide the option. At least one automotive supplier is working on an 
electromechanical system that moves the head restraint up to 40 mm 
forward when a rear sensor in the vehicle anticipates a rear 
impact.\106\
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    \105\ Wiklund, Kristina; Larsson, H[aring]kan (1 February 1998). 
``Saab Active Head Restraint (SAHR)--Seat Design to Reduce the Risk 
of Neck Injuries in Rear Impacts.'' Journal of Passenger Cars.
    \106\ ``Can a high-tech headrest reduce whiplash injuries,'' 
Automotive News, August 14, 2022, https://www.autonews.com/suppliers/high-tech-headrest-designed-reduce-whiplash-injuries.
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    In the early 1990s, General Motors (GM) Research and Development 
Center undertook an in-depth study of seat characteristics to improve 
occupant safety in rear impacts. In general, the GM seat design 
fostered movement of the pelvis rearward and into the lower portion of 
the seat back frame in a way that would preclude ramping and reduce the 
moment arm on the seat back. A key design component was to balance the 
stiffness of the seat resisting the rearward movement of the pelvis 
against the ability of the seat back frame to resist backward rotation. 
GM established their own quasi-static test for the purposes of assuring 
that a given seat met the design parameters. It was a destructive test 
that made use of a 50th percentile male dummy loaded rearward into the 
seat back through the lumbar joint. The dummy was free to move up, 
down, and sideways during rear loading. The test also allowed the seat 
back to rotate rearward and twist in a manner similar to what was 
observed in sled testing. Eventually, GM's seat design targets were 
published by SAE International.\107\ The targets were derived from 
various measurements taken during their quasi-static test. The targets 
contained many more parameters than FMVSS No. 207's single requirement 
to withstand a 373 Nm (3,300 in-lb) moment (see table 1 for a list of 
the parameters). Notably, the GM parameters included a criterion that 
limited the seat stiffness to no more than 25 kN/m, while attempting to 
assure that the seat had sufficient energy absorbing properties. GM 
stressed that simply raising the FMVSS No. 207 moment beyond 373 Nm 
would not achieve a desirable seat design. According to GM, increasing 
only the seat back's stiffness would reduce the beneficial effects of 
yielding.
---------------------------------------------------------------------------

    \107\ Viano, David C. ``Role of the seat in rear crash safety.'' 
Warrendale, PA: Society of Automotive Engineers, 2002. 514 (2002).
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    A seat design feature that was rare 25 years ago, but appears to be 
much more common in modern seats is a dual recliner 
system.108 109 A dual recliner system places gear mechanisms 
controlling the static recline angle on both sides of the seat. This 
improvement significantly strengthened production seats and reduced 
longitudinal axis twisting.\110\ The agency does not have an estimate 
of the current level of implementation of dual recliners and requests 
that commenters provide these data.
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    \108\ About one third of the seats tested by the agency in 1998 
were dual recliners. This was a convenience sample not intended to 
be representative of the fleet. Molino L (1998), Determination of 
Moment-Deflection Characteristics of Automobile Seat Backs, NHTSA, 
November 25, 1998. See Regulations.gov, Docket document no. NHTSA-
1998-4064-0026.
    \109\ Viano, David C., et al. ``Occupant responses in 
conventional and ABTS seats in high-speed rear sled tests.'' Traffic 
injury prevention 19.1 (2018): 54-59.
    \110\ Herbst, B.R., Meyer, SE, Oliver, A.A., and Forrest, S.M. 
Rear impact test methodologies: quasistatic and dynamic. Proceedings 
of 21st International Technical Conference on the Enhanced Safety of 
Vehicles, 2009. Stuttgart, Germany.
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    An IIHS study of contemporary production seats claims that a wide 
range of seating systems have achieved a balance between low-speed 
protection while maintaining structural integrity at higher speeds and 
occupant retention.\111\ This study conducted rear impact sled testing 
on 26 modern production seats at a [Delta]V of 36.5 km/h (22.7 mph) 
using a 78 kg (172 lb) Hybrid III 50th percentile male dummy. The 
maximum dynamic seat back rotation ranged from 15[deg] to 47[deg] from 
the initial angle and the dummy was retained by all seat backs. During 
testing, the vertical displacements of the dummies was between 41 mm to 
144 mm. The authors concluded that a majority of tested production 
seats provided adequate occupant retention at a [Delta]V of 36.5 km/h 
(22.7 mph), but with a range of performance metrics. Moreover, all 26 
seats tested by IIHS had ``Good'' ratings for low-speed rear impact 
protection as determined by a separate IIHS test using the BioRID dummy 
at a [Delta]V of 16 km/h (10 mph).
---------------------------------------------------------------------------

    \111\ Edwards, Marcy A., et al. ``Seat design characteristics 
affecting occupant safety in low-and high-severity rear-impact 
collisions.'' IRCOBI Conference, Florence, Italy, IRC-19-11. 2019.
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C. Non-Contact Injuries

    This section outlines a segment of the literature concerning non-
contact neck and thorax injuries resulting from rear collisions.
1. Neck Injuries
    The term whiplash has been used since the 1920s to describe various 
symptoms or signs of cervical spine injury in motor vehicle accidents. 
The first case series studies on motor vehicle whiplash injury were 
published in the early 1950s.\112\ Later in the 1960s, studies were 
conducted on the mechanisms of whiplash injury.\113\ These and related 
efforts developed the notion that the whiplash injury rate could be 
reduced by preventing hyperextension of the neck. The initial version 
of FMVSS No. 202 mandated head restraints as a countermeasure to this 
type of neck injury.\114\ After the mandate was introduced, a 
statistical analysis of crash data sets found modest improvements in 
the whiplash injury rates.\115\ A 1982 NHTSA report of rear impacts in 
passenger cars, for example, found that integral head restraints 
reduced whiplash injury risk by 17% while adjustable restraints reduced 
the risk by 10%.\116\ A Swedish study found

[[Page 58017]]

a similar 20% decrease in neck injuries as a result of the head 
restraint.\117\ However, the persistence of frequent whiplash injury 
motivated later studies of cervical spine dynamics in rear collisions.
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    \112\ Gay, James R., and Kenneth H. Abbott. ``Common whiplash 
injuries of the neck.'' Journal of the American Medical Association 
152.18 (1953): 1698-1704.
    \113\ MacNab, Ian. ``Whiplash injuries of the neck.'' 
Proceedings: American Association for Automotive Medicine Annual 
Conference. Vol. 9. Association for the Advancement of Automotive 
Medicine, 1965.
    \114\ NHTSA, FMVSS No. 202 Head Restraints for Passenger 
Vehicles Final Rule, Final Regulatory Impact Analysis, Nov. 2004, 
Docket No. NHTSA-2004-19807.
    \115\ O'Neill, Brian, et al. ``Automobile head restraints--
frequency of neck injury claims in relation to the presence of head 
restraints. American journal of public health 62.3 (1972): 399-406. 
Nygren, Ake, Hans Gustafsson, and Claes Tingvall. Effects of 
different types of headrests in rear-end collisions. No. 856023. SAE 
Technical Paper, 1985.
    \116\ Kahane, Charles J. An Evaluation of Head Restraints, NHTSA 
Publication No. DOT HS 806 108, Washington, DC, 1982, pp. 154-160 
and 181-197.
    \117\ Nygren, Ake, Hans Gustafsson, and Claes Tingvall. Effects 
of different types of headrests in rear-end collisions. No. 856023. 
SAE Technical Paper, 1985.
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    In 1995, the Quebec Task Force on Whiplash Associated Disorders 
categorized whiplash injuries into five grades, 0 to IV, in order of 
increasing severity. For convenience, we will continue to refer to 
whiplash associated disorders as whiplash injuries. The Quebec study 
determined that 90% of insurance claims fell within grades 0 and I 
where there was no clear pathology based on existing technology, but 
symptoms may include neck pain, headache, memory loss, jaw pain, 
hearing disturbance, and dizziness. Grades II and III include 
musculoskeletal and neurological signs; grade IV contains cervical 
fractures and dislocations. The most severe soft tissue whiplash type 
injury occurring in grade IV is typically characterized by disc 
herniation and is often accompanied by facet-joint hematoma, peripheral 
spinal nerve and spinal cord contusion or articular process 
fracture.\118\ The findings of a study on very low velocity rear 
collisions \119\ led the authors to conclude that a biomechanical 
``limit of harmlessness'' for whiplash exists for rear collision 
[Delta]V between 10 to 15 km/h. The author goes on to explain that this 
is the speed range below which there were no anatomical signs of 
injury, but did not rule out ``psychological injury.''
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    \118\ Davis, Charles G. ``Mechanisms of chronic pain from 
whiplash injury.'' Journal of forensic and legal medicine 20.2 
(2013): 74-85.
    \119\ Castro, W.H., et al. Do whiplash injuries occur in low-
speed rear impacts? European spine journal: official publication of 
the European Spine Society, the European Spinal Deformity Society, 
and the European Section of the Cervical Spine Research Society 6.6 
(1997): 366-375.
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    Basic research of rear collision neck kinematics indicate that neck 
and head dynamics occur through a complex process. The neck may 
experience compression, tension, shear, torsion, retraction, 
protraction, flexion, and extension to varying degrees and at different 
points in time. Studies on cervical spine kinematics in rear collisions 
by Svensson, et al.\120\ and McConnell, et al.\121\ in 1993, Geigl, et 
al.\122\ in 1994 and Panjabi, et al.\123\ in 1998 noted that the neck 
displayed an unnatural S-shaped curve in the early stages of the 
kinematics due to retraction, and Panjabi hypothesized that neck injury 
may occur before head contact with the head restraint. In a study by 
Feng, et al.,\124\ the authors described early rear impact neck 
dynamics through a series of kinematic spinal processes. The authors 
noted that rear impact forces are at first distributed across the 
occupant's torso through the seat back and then are transmitted to the 
neck and head. These initial forces impose torso straightening and 
likely movement of the occupant's torso up the seat back. The authors 
hypothesize that axial compression is generated in the spinal column, 
which travels up the neck to the head. As the head moves upwards axial 
tension is then proposed to develop in the neck through 
disproportionate movement of the head and neck due to a constrained 
torso. As these first actions evolve the head lag phenomenon (also 
described in an earlier 1976 study \125\) or retraction develops 
through a delay between the forward motion of an occupant's torso and 
head. Retraction leads to shear in the cervical column and curvature of 
the neck is reduced. These theorized actions occur before the head 
contacts the head restraint.
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    \120\ Svensson, Mats Y., et al. Rear-end collisions-a study of 
the influence of backrest properties on head-neck motion using a new 
dummy neck. No. 930343. SAE Technical Paper, 1993
    \121\ McConnell, Whitman E., et al. Analysis of human test 
subject kinematic responses to low velocity rear end impacts. No. 
930889. SAE Technical Paper, 1993.
    \122\ Geigl, B.C., et al. ``The movement of head and cervical 
spine during rear end impact.'' Proceedings of the International 
Research Council on the Biomechanics of Injury conference. Vol. 22. 
International Research Council on Biomechanics of Injury, 1994.
    \123\ Panjabi, Manohar M., et al. ``Mechanism of whiplash 
injury.'' Clinical Biomechanics 13.4-5 (1998): 239-249.
    \124\ Luan, Feng, et al., ``Qualitative analysis of neck 
kinematics during low-speed rear-end impact.'' Clinical Biomechanics 
15.9 (2000): 649-657.
    \125\ Ewing CL., Thomas D., Lustick L., Muzzy W.H., et al. The 
Effect of Duration, Rate of Onset and Peak Sled Acceleration on the 
Dynamic Response of the Human Head and Neck. Proceedings of the 20th 
Stapp Car Crash Conference, Dearborn, MI, Society of Automotive 
Engineers, Inc., 1976.
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2. Thorax Injuries in High-Speed Rear Impacts
    A recent NHTSA research study was conducted with 14 PMHS tests in 
rear facing seats in frontal collisions at a [Delta]V of 56 km/h for 
different recline angles and seat types to investigate thorax 
injuries.\126\ The structure supporting the seat back was rigidized to 
avoid unpredictable permanent deformations of the seat during the 
event. The goal of the study was to examine non-standard seating 
configuration for vehicles with automated driving systems (ADS) with 
reclined rear-facing seats in a frontal collision. It may also, 
however, provide some insight into rear impact dynamics because the 
loading is rearward with respect to the seat back orientation. 
Additionally, the 56 km/h [Delta]V test is very severe for a rear 
impact. The CISS data reported in section II.B indicates this speed 
represents more than 95% of all towaway rear impacts. The authors found 
that rib fractures occurred in the PMHSs due to a complex combination 
of chest compression and expansion with upward shear loading. The 
majority of rib fractures occurred after peak chest compression when 
the abdominal contents shifted rearward and upward into the thorax due 
to the ramping motion of the PMHS, which created a combined loading 
(compression/tension and shear) to the thorax. Similar magnitudes of 
rib strains were observed regardless of seat types, while strain modes 
varied according to recline angle and seat type. Fewer injuries were 
seen with a more upright 25-degree seat back, compared to a more 
typical initial seat angle of 45-degree seat back.
---------------------------------------------------------------------------

    \126\ Kang YS, et al. ``Thoracic responses and injuries to post-
mortem human subjects (PMHS) in rear-facing seat configurations in 
high-speed frontal impacts,'' Twenty-Seventh Enhanced Safety of 
Vehicles Conference (2023).
---------------------------------------------------------------------------

D. Summary

    While progress has been made in understanding rear impact injuries, 
the literature continues to point toward the need for a greater 
understanding before conclusions can be drawn about the exact 
mechanisms of injury and the risk factors involved, particularly in 
regards to whiplash.\127\ Likewise, important safety improvements have 
been made in production seats over the last 50 years and a greater 
understanding of the relationship between seat back characteristics and 
injury has been achieved, but questions remain with respect to 
precisely quantifying protective characteristics. The continued 
uncertainty around how best to protect occupants as well as the varied 
approaches and developments in rear impact technology suggests that, as 
NHTSA considers amendments to FMVSS Nos. 207 and 202a, there is value 
in preserving industry flexibility in seat back and head restraint 
design and strength parameters to allow further

[[Page 58018]]

research into and development of these systems.
---------------------------------------------------------------------------

    \127\ Holm, Lena W., et al. ``The burden and determinants of 
neck pain in whiplash-associated disorders after traffic collisions: 
results of the Bone and Joint Decade 2000-2010 Task Force on Neck 
Pain and Its Associated Disorders.'' Journal of manipulative and 
physiological therapeutics 32.2 (2009): S61-S69.
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V. Petitions for Rulemaking at Issue in This Document

A. Statutory and Regulatory Background

    Under 5 U.S.C. 553(e), 49 U.S.C. 30162(a)(1) and 49 CFR part 552, 
interested persons can petition NHTSA to initiate a rulemaking 
proceeding. Upon receipt of a properly filed petition, the agency 
conducts a technical review of the petition, material submitted with 
the petition, and any additional information.\128\ After conducting the 
technical review, NHTSA determines whether to grant or deny the 
petition.\129\ The Safety Act states that all FMVSS requirements must 
be practicable, meet the need for motor vehicle safety, and be stated 
in objective terms.\130\ Accordingly, NHTSA will initiate a rulemaking 
only if the agency believes that the proposed rule would meet these 
criteria. If a petition is granted, a rulemaking proceeding is promptly 
initiated in accordance with statute and NHTSA procedures. A grant of a 
petition and a commencement of a rulemaking proceeding do not, however, 
signify that the rule in question will be issued. That decision is made 
on the basis of all available information developed in the course of 
the rulemaking proceeding, in accordance with statutory criteria.\131\ 
If a petition under this section is denied, the reasons for the denial 
are published in the Federal Register.\132\
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    \128\ 49 U.S.C. 30162(a)(1); 49 CFR 552.6.
    \129\ 49 CFR 552.8; see also 49 U.S.C. 30162(c).
    \130\ 49 U.S.C. 30111(a).
    \131\ 49 CFR 552.9; see also 49 U.S.C. 30162(c).
    \132\ 49 CFR 552.10.
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B. Petition of Kenneth J. Saczalski

    On October 28, 2014, Kenneth J. Saczalski of ERST petitioned NHTSA 
to amend FMVSS Nos. 207 (Seating systems), 213 (child restraint 
systems), and 301 (Fuel system integrity). Saczalski requested that 
NHTSA increase the static strength requirement for seat backs by a 
factor of six and implement a new dynamic requirement. The dynamic 
requirement would assess the seat back of a vehicle by performing a 
rear impact crash test with a 50th percentile male ATD positioned in 
the seat. The petition also suggested adding a rear impact requirement 
to FMVSS No. 213, ``Child restraint systems,'' and implementing a new 
requirement for rear seats that would resist the forces of loose cargo 
that may be stowed behind the rear seats.
1. FMVSS No. 207, Seating Systems
    Saczalski seeks an amendment to FMVSS No. 207, S4.2(d) to increase 
the rearward force that occupant seats must withstand from a 373 Nm 
(3,300 in-lb) moment measured about the H-point to a 2,260 Nm (20,000 
in-lb) moment measured from the pivot intersection of the seat back 
structure and the seat cushion frame.\133\ While this ostensibly 
represents an increase by a factor of six, because FMVSS No. 202a 
effectively requires seat backs to withstand a 654 Nm (5,790 in-lb) 
moment, this would only increase the performance requirement by a 
factor of 3.5 above current requirements, if measured about the H-
point. The actual factors would be closer to a factor of 5.4 above the 
required FMVSS No. 207 moment and 3.1 above the FMVSS No. 202a 
requirement, depending on the relative position of the seat pivot with 
respect to the H-point.\134\
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    \133\ ``Rearward force'' means the force against the rear side 
of an occupant seat, regardless of orientation. For a forward-facing 
seat, this would mean a force applied in the rearward longitudinal 
direction, whereas with a rear-facing seat, this would mean a force 
applied in the forward longitudinal direction.
    \134\ Selecting the seat pivot point as the location for the 
moment measurement reduces the force needed to produce a given 
moment. Assuming a vertical distance of 535 mm from the H-point to 
the location of force application and a vertical distance of 595 mm 
from the seat pivot to the force location results in a 10% reduction 
in force for the same moment measure about the pivot compared to the 
H-point.
---------------------------------------------------------------------------

    Saczalski also made a more general request that FMVSS No. 207 seat 
strength testing be conducted ``to ultimate strength levels'' that 
establish a seat's capacity to withstand crash forces. According to 
Saczalski, testing must be repeated to examine strength variations 
relating to adjustable seat components, such as height adjusters. 
Saczalski does not, however, provide a specific set of performance 
requirements or tests that he asserts should be conducted. Saczalski 
also requested that NHTSA add a requirement that seats not experience a 
``sudden load collapse'' (i.e., a failure of structural components that 
causes the occupant support loading to suddenly drop off) of 400 pounds 
force or greater within a short span of rearward deformation. According 
to Saczalski, this testing should be done using a ``torso body-block'' 
device that replicates the upper body weight of a 95th percentile male.
2. Use of FMVSS No. 301, ``Fuel System Integrity,'' To Test Seats
    Saczalski petitioned NHTSA to implement a new seat back requirement 
using the dynamic rear-end crash test prescribed in the latest revision 
of the fuel system integrity test described in FMVSS No. 301. In this 
test, a stationary vehicle is struck in the rear by a 1,368 kg (3,015 
lb) deformable barrier travelling at 80 km/h (50 mph). The barrier 
overlaps the rear end of the vehicle by 70%.
    Saczalski asserted that a dynamic, full vehicle test is needed in 
addition to the static requirements discussed above. The main purpose 
of such a test would be to fully assess the safety of children in rear 
seats who may be exposed to collapsing front seat backs. Saczalski 
cites in his petition a 2008 study by Children's Hospital of 
Philadelphia (CHoP).\135\ The study examined risk levels through an 
epidemiological study of real-world crashes, and found that in a rear-
end crash, children seated directly behind a seat back that yielded 
exhibited about twice the risk of injury as children seated behind a 
seat back that did not yield. Saczalski has asked for a dynamic test to 
be run with Hybrid III 95th percentile male dummies (HIII-95M) in the 
front seats with 12-month-old dummies seated directly behind in 
forward-facing child restraints.\136\ He recommends a pass/fail limit 
on front seat back rotation of no more than 25 degrees rearward from 
its initial seat back orientation. He also recommends that NHTSA impose 
pass/fail requirements based on dummy measurements within the head, 
neck, chest, and extremities. This would apply to the HIII-95M and the 
12-month-old dummies. Saczalski recommends pass/fail requirements for 
both dummies equivalent to ``their respective NHTSA injury reference 
levels for the head, neck, chest, and extremities.'' \137\
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    \135\ Jermakian JS, Arbogast KB, Durban DR, Kallan NJ (2008), 
Injury risk for children in rear impacts: role of the front seat 
occupant, 52nd AAAM Annual Conference, Annals of Advances in 
Automotive Medicine, October 2008.
    \136\ The 12-month-old dummy, known as the (CRABI) dummy, is 
already integrated into subpart P of part 572.
    \137\ Injury reference values recommended by NHTSA for the CRABI 
and HIII-95M, when used to assess air bags, are contained within: 
Eppinger R, Sun E, Kuppa S, Saul R (2000), Supplement: development 
of improved injury criteria for the assessment of advanced 
automotive restraint systems-II, National Highway Traffic Safety 
Administration, March 2000.
---------------------------------------------------------------------------

    Saczalski also suggested that the test be run with 20 kg (44 lb) 
simulated luggage cases in the trunk area, which he stated could push 
the rear seat forward. According to Saczalski, such a requirement will 
guard against injuries due to the intrusion of a rear seat occupied by 
a child into a yielding front seat back.

[[Page 58019]]

3. FMVSS No. 213, Child Restraint Seats
    Saczalski asked NHTSA to include a rear impact requirement for 
child restraint systems within FMVSS No. 213, which does not contain 
such requirements. He suggested using the same test and performance 
criteria as the European standard for child restraint systems, United 
Nations Economic Commission for Europe Regulation 44 (ECE R.44),\138\ 
but run at a higher test speed of 40 km/h.\139\ The ECE standard 
contains requirements for various sized child dummies subjected to a 30 
km/h rear impact. Like FMVSS No. 213, the European standard also 
includes requirements for a frontal impact, but those are not discussed 
in Saczalski's petition.
---------------------------------------------------------------------------

    \138\ Uniform Provisions Concerning the Approval of Restraining 
Devices for Child Occupants of Power-Driver Vehicles, (Child 
Restraint Systems), ECE R.44, E/ECE/324/Rev (unece.org).
    \139\ UNECE Regulation No. 44, Uniform provisions concerning the 
approval of restraining devices for child occupants of power-driven 
vehicles (``Child Restraint System'').
---------------------------------------------------------------------------

C. Petition of Alan Cantor

    In a letter dated September 28, 2015, Alan Cantor of ARCCA 
petitioned NHTSA to revise FMVSS No. 207 by implementing new 
requirements for seat back strength involving a crash test with an ATD. 
He also requested that NHTSA reinstate a provision to FMVSS No. 209, 
``Seat belt assemblies,'' that he states would prevent occupant 
injuries in rear impacts.
1. Use of FMVSS No. 301, ``Fuel System Integrity,'' To Upgrade FMVSS 
No. 207
    Cantor requested a dynamic test to assess seat back loading by 
occupants of different sizes. He envisioned the use of the current 
FMVSS No. 301 procedure with Hybrid III 50th Percentile male dummies 
(HIII-50M). Additionally, Cantor requested that a test be performed at 
oblique impact angles to assess the potential of excessive seat back 
twisting that Cantor stated could facilitate rearward ramping and an 
out-of-position orientation of the occupant in the seat during 
subsequent impacts. A full vehicle test was also envisioned, but 
alternatively Cantor suggested that a sled test could be run using an 
impulse equivalent to that produced by the dynamic procedure. Cantor 
did not request a change to the static requirements of FMVSS No. 207, 
nor did he call for the use of rear seated child dummies in the 
dynamic, full vehicle test. Under Cantor's rationale, the test with the 
HIII-50M dummies would serve as the basis for a new set of FMVSS 
requirements. The requirements would apply to front seats as well as 
rear ``bucket'' seats, such as those within minivans, that he suggests 
may also have a propensity to collapse.
2. Rearward Rotation Limit and Structural Symmetry Requirement
    Cantor recommended a pass/fail limit for rearward seat back 
rotation of no more than 15 degrees from its initial seat back 
orientation (measured in real-time during the test). For the oblique 
impacts, there would be a requirement that the differential rearward 
deflection of the seat back is no more than 10 degrees between the left 
and right sides. According to Cantor, this will assure structural 
symmetry of the seat to prevent excess twisting of the seat under load, 
which can lead to ramping or out-of-position orientation of an occupant 
if subsequent impacts occur.
3. Additional Dynamic Testing and NCAP Implementation
    Cantor also requested another dynamic test to assess seat back 
loading to be performed with a Hybrid III 95th male dummy (HIII-95M) 
and to incorporate results into the NCAP star rating for the vehicle. 
This test would be performed in a manner similar to the current FMVSS 
No. 301 procedure, but at an impact speed of the barrier that is 8 km/h 
(5 mph) faster than the current FMVSS No. 301 speed. He argues that it 
would serve to inform consumers on whether a given vehicle seat back 
has the propensity to collapse. Cantor states it would also provide 
incentive to manufacturers to develop enhancements to rear impact crash 
protection.
    Cantor recommended the same pass/fail limit for rearward seat back 
rotation for the NCAP tests as he recommended for the FMVSS No. 301 
impacts. Cantor did not specify how the results would be factored into 
the NCAP rating.
4. FMVSS No. 209, Seat Belt Assemblies
    Cantor requested that NHTSA restore S4.1(b), which NHTSA deleted in 
a final rule published in 1999.\140\ This provision required the lap 
belt portion of the seat belt be designed to remain on the pelvis under 
all crash conditions. Cantor states that restoring S4.1(b) would assure 
that vehicles will be equipped with seat belt technologies that prevent 
ramping in rear impact crashes.
---------------------------------------------------------------------------

    \140\ 64 FR 27203 (May 19, 1999).
---------------------------------------------------------------------------

D. NHTSA's Analysis of Saczalski and Cantor Petitions

    NHTSA is denying in part the Saczalski and Cantor petitions as they 
pertain to the following recommendations: Cantor's requested amendments 
to NCAP and request to restore anti-ramping language to FMVSS No. 209, 
and Saczalski's requests to add a rear impact test to FMVSS No. 213 and 
a cargo test requirement to FMVSS No. 207. As part of this rulemaking 
effort to update FMVSS No. 207 and to facilitate informed comment, 
NHTSA is granting the petitions in part with regard to updating the 
strength requirement in FMVSS No. 207, the structural symmetry 
requirement requested by Cantor, and the possible development of new 
test procedures for seat back strength under FMVSS No. 207. NHTSA notes 
that, at this time, insufficient information has been provided to 
support the petitioners' suggested specific strength levels or test 
designs, but NHTSA seeks comment on this issue. The remainder of this 
section provides NHTSA's opinions on the recommendations in the 
petitions to provide context and information to support informed 
comment on an update to FMVSS No. 207. Later in this document, we 
discuss NHTSA's current thinking on an integrated and unified approach 
to rear impact protection and seeks comment on that approach.
1. Analysis of Data and Research Provided by Cantor and Saczalski 
Regarding Safety Need
    In the past, NHTSA and petitioners on this topic have not been able 
to demonstrate that a safety need exists regarding the seat back 
strength requirement in FMVSS No. 207.\141\ In their petitions, 
Saczalski and Cantor both implied that factors related to child safety 
have given rise to a new safety need for stronger seat backs. NHTSA 
acknowledges that there is evidence that, in some crash scenarios, seat 
back deformation or rearward movement due to component failure can lead 
to injury, but NHTSA believes that the petitioners have not provided 
sufficient supporting data to demonstrate a worsening safety need 
related to seat back strength compared to NHTSA's past determination. 
NHTSA discusses the materials provided by petitioners below and seeks 
comment on this question.
---------------------------------------------------------------------------

    \141\ See discussion in section III.B.10 of this document and 69 
FR 67068 (Nov. 16, 2004).
---------------------------------------------------------------------------

    In support of his petition, Saczalski references the CHoP study. 
NHTSA agrees with Saczalski that the 2008 CHoP study is useful for 
understanding the levels of risk to which children in rear seats are 
exposed, but the CHoP study did not determine that this risk was 
associated with front seat back strength. The information submitted by 
petitioners did not provide new or pertinent information to build upon 
the

[[Page 58020]]

CHoP study or further demonstrate a safety need.
    Saczalski provided NHTSA with his own publications, including one 
from the 2014 annual meeting of the International Federation of 
Automotive Engineering Societies (FISITA).\142\ This paper described 13 
cases of infant fatalities in rear-end crashes in which the infant was 
seated behind an occupied front seat. However, as with the CHoP study, 
Saczalski's paper did not provide additional insight on whether the 
fatalities were associated with front seat back strength. Moreover, 
because most of the fatalities occurred in vehicles that were built 
prior to MY 2000, the cases he cites may not reflect the lower level of 
risk associated with new vehicles. Since then, improvements have been 
made to FMVSS Nos. 202a, 301, and other standards that may impact the 
conclusions reached in the CHoP study and Saczalski's paper. In 
addition, changes in manufacturer's design targets and the more 
frequent use of dual recliners may have resulted in seat designs that 
are generally stronger.
---------------------------------------------------------------------------

    \142\ Saczalski K, Pozzi M, Burton J, Saczalski T (2014), 
Experimental and field accident analysis study of factors effecting 
child occupant injury risk and safety in rear impacts, 2014 Annual 
FISITA Meeting, Paper No. F2014-AST-013, 2014.
---------------------------------------------------------------------------

    Saczalski also provided the results of several sled tests with 
crash test dummies, which he argues demonstrate that the seat back of a 
front-seated adult can collapse on a child sitting in the rear in a 48 
km/h rear-end impact. While these tests may illustrate the potential 
consequences of seat back deformation or failure, they simply reinforce 
a finding of which NHTSA is already aware: that it is possible for some 
seat backs to yield in a severe rear-end impact in a way that could 
potentially injure occupants.
    Finally, according to Saczalski, fatality counts within the Fatal 
Accident Reporting System (FARS) from 2001-2011 show that fatalities in 
infants (0-12 months) have doubled since 1990-2000, from which he 
infers a worsening safety need.
    NHTSA believes that the conclusion Saczalski draws from this data 
is inaccurate. NHTSA has queried FARS for infant and adolescent 
fatalities where the child was known to be restrained in a rear seat, 
non-ejected, in a non-rollover, rear impact. Over the last 15 years 
captured in the study, the average fatality rate is 7.7 per year, 
ranging from 1 to 15 per year (See Figure V.1). There is a great deal 
of scatter and no clear fatality trend over time. If the data are 
expanded to all children up to an age of 5, the average fatality rate 
is 31.9 per year, ranging from 22 to 60 (See Figure V.2). Again, there 
is no clear trend in the data. The data for the 0-5-year-olds have less 
scatter than that for the 0-12-month-olds. This latest data is not 
supportive of a claim that there is a fatality risk that continues to 
increase. NHTSA notes that these data provide an estimate of all-cause 
mortality and therefore provide no insights into whether front row seat 
performance contributed to the child's death.
BILLING CODE 4910-59-P
[GRAPHIC] [TIFF OMITTED] TP16JY24.014


[[Page 58021]]


[GRAPHIC] [TIFF OMITTED] TP16JY24.015

BILLING CODE 4910-59-C
2. Rear Structure Intrusion
    Saczalski states in his petition that there are phenomena other 
than front seat back failure and ramping that create risk to children 
in rear seats. He notes that rear-seated children in rear-end 
collisions are often injured by poorly designed rear structures that 
push children forward into the front seat back. He supports this claim 
using a 2008 study of NASS-CDS data, which looked at the risk to 
children seriously injured in rear impacts and indicated that injury 
caused by intrusion from the rear seating area is a larger problem than 
deforming front seat.\143\ NHTSA appreciates the analysis done by 
Saczalski and agrees that there is evidence to support a finding that 
there is a safety risk to children in the rear seat in a rear impact 
crash. NHTSA also agrees that this risk involves more factors than just 
front seat back collapse, such as rear structure intrusion. NHTSA seeks 
comment on the significance of the intrusion issue in the overall 
context of rear impacts and whether a practicable solution to this 
issue exists. NHTSA notes that the 2006 revision to FMVSS No. 301, Fuel 
system integrity, which would not have been in place for the model 
years of the vehicles Saczalski studied, may have induced changes to 
rear vehicle structures that mitigated the intrusion problem.
---------------------------------------------------------------------------

    \143\ Viano D, Parenteau C (2008), Field Accident Data Analysis 
of 2nd Row Children and Individual Case Reviews, SAE Technical Paper 
2008-01-1851.
---------------------------------------------------------------------------

    NHTSA wishes to emphasize that Saczalski and Cantor do not appear 
to have considered whether increasing the requirement for seat strength 
would have any unintended negative safety impacts. This document 
discusses at length the literature, such as the 1997 Prasad study, 
which suggest a possible association between significantly stiffer 
seats and increased incidence of whiplash and other non-contact 
injuries. NHTSA seeks comment on these potential negative safety 
impacts, which the agency believes is critical to understanding the 
overall safety problem in occupant protection in rear impact and 
whether changes to FMVSS No. 207 will meet a need for safety.
3. Cost and Practicability
    Cantor argues in his petition that upgrading seat back strength 
would not impose a major cost on manufacturers, claiming that many 
modern vehicles have stronger seats compared to those in 1989 even in 
absence of a change to FMVSS No. 207. To support this claim, he cites 
his own testing, in which he claims to have studied newer vehicles 
using the FMVSS No. 207 procedure and found that they ``tested out'' 
somewhere between 2.5 to 10 times the current compliance level (373 
Nm). Based on his own testing, he concludes that it would not be cost 
prohibitive for original equipment manufacturers that use less strong 
seats to increase seat back strength, and he argues that an upgrade to 
the standard is needed to assure all seat backs have a minimum 
strength.
    NHTSA does not believe that Cantor's examples of actual seat back 
strength in the modern vehicles provide new or better data over what 
was known to NHTSA in 2004, when NHTSA terminated a rulemaking to 
increase seat back strength. The variance seen in Cantor's test results 
is consistent with that seen in the Severy data from the 1960s. It was 
also seen in data in a 1998 report prepared by NHTSA.\144\
---------------------------------------------------------------------------

    \144\ Molino L (1998), Determination of Moment-Deflection 
Characteristics of Automobile Seat Backs, NHTSA, November 25, 1998. 
See Regulations.gov, Docket document no. NHTSA-1998-4064-0026.
---------------------------------------------------------------------------

    NHTSA agrees that increasing seat back strength is technically 
feasible. Any rulemaking action to change the seat back strength 
requirement, however, must be practicable, meet the need for motor 
vehicle safety, and be stated in objective terms. As part of this 
analysis, a rulemaking action would assess whether this would be a 
cost-effective way to increase overall motor vehicle safety.

E. Assessment of the Specific Recommendations by Cantor and Saczalski

    In this section, NHTSA presents its assessment of specific matters 
petitioned for by Cantor and Saczalski. The first section discusses the 
matters on which NHTSA is granting the petitions and initiating 
rulemaking and provides NHTSA's opinions on those specific petitioned-
for issues to facilitate informed comment. The second section covers 
the issues on which NHTSA is

[[Page 58022]]

denying in part and provides the reasons for denial as required in 49 
CFR part 552.
1. Matters on Which NHTSA Is Granting the Petitions
(a) Amend FMVSS No. 207 To Increase Seat Back Moment Requirement and 
Alter Load Application Method
    Saczalski asked NHTSA to raise the torque requirement about the 
seat back pivot to 2,260 Nm (20,000 in-lb). This would raise the 
current FMVSS No. 207 requirement of 373 Nm (3,300 in-lb) by a factor 
of about 5.4 and by a factor of about 3.1 above the FMVSS No. 202a 
requirement of 654 Nm (5,788 in-lb). In addition, Saczalski recommended 
that the load be applied through a ``body block'' representing a 95th 
percentile male, rather than to the upper member of the seat frame. 
NHTSA is granting the petition on the torque requirement and static 
test design issues in part, is initiating rulemaking to consider 
whether to upgrade FMVSS No. 207 on these topics and seeks comment on 
the analysis below.
    Saczalski did not explain why a torque limit of 2,260 Nm was 
preferable to other limits that NHTSA has considered previously (See 
table V.1) and would not result in the potential safety harms discussed 
above. Furthermore, Saczalski does not provide a compelling reason why 
a body block test would be the most effective way to test rearward 
moment strength statically. NHTSA notes that Saczalski is also 
requesting a dynamic requirement, and he did not explain why amending 
the FMVSS to use a body block for the static test would be necessary if 
NHTSA were to accept his recommendation to incorporate a dynamic test 
with a more biofidelic dummy.

                       Table V.1--Past Recommendations for Revising the Quasi-Static Seat Back Torque Requirement in FMVSS No. 207
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                   Current standard                                             Recommendations
                                 -----------------------------------------------------------------------------------------------------------------------
         Test reference              FMVSS No. 207                                              Saczalski (1989                         Saczalski (2014
                                     (since 1968)        Severy (1969)     NHTSA (1974 NPRM)       petition)       Viano \1\ (2003)        petition)
--------------------------------------------------------------------------------------------------------------------------------------------------------
H-point moment, min.............  373 Nm (3,300 in-   11,300 Nm (100,000  373 Nm (3,300 in-   6327 Nm (56,000 in- 1700 Nm (15,000 in- 2260 Nm (20,000 in-
                                   lb).                in-lb).             lb).                lb).                lb).                lb).
Seat back requirement...........  ``withstand''       ..................  ..................  ``withstand''       specifics given     ``withstand''
                                   torque.                                                     torque.             below.              torque.
Seat back rotation, max.........  ..................  10 deg............  40 deg............
Load drop limit, max............  ..................  ..................  ..................  ..................  2000 N over         1780 N ``sudden''.
                                                                                                                   10[deg] rot.
Load application................  upper member of     upper member of     upper member of     upper member of     thru HIII-50M       thru HIII-95M body
                                   seat back frame.    seat back frame.    seat back frame.    seat back frame.    lower torso.        block.
Seat stiffness, max.............  ..................  ..................  ..................  ..................  25 kN/m...........
Frame compliance, max...........  ..................  ..................  ..................  ..................  2.0 deg/kN........
Load limit, min.................  ..................  ..................  ..................  ..................  7.7 kN............
Seat twist, max.................  ..................  ..................  ..................  ..................  15 deg............
Dummy H-point upward displ., max  ..................  ..................  ..................  ..................  50 mm.............
 (design target only).
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Viano's quasi-static test equipment and procedure represents more of an alternate test method than a simple revision to FMVSS No. 207. Details are
  described in Viano (2003), ``Resolving the debate between rigid (stiff) and yielding seats: seat performance criteria for rear crash safety,'' cited
  earlier.

    Saczalski also suggested that NHTSA impose a requirement so that, 
when tested to failure, there is no sudden drop in load of 1,780 N (400 
lb-f) or greater within a short span. NHTSA is also granting the 
petition on this issue in part. NHTSA is aware of others who have 
recommended similar changes in the past to assure a gradual deformation 
of seat back components. NHTSA notes that Saczalski did not suggest an 
objective and practicable test procedure. Depending on how a test is 
carried out, a sudden load drop in a quasi-static test may not 
necessarily indicate an unsafe design. Even a drop to zero is not 
necessarily problematic if a slight perturbation in backward movement 
brings the load back up. NHTSA seeks comment on this requirement. What 
safety benefits could be obtained from such a requirement? Is there a 
practicable and objective test procedure that can be developed?

(b) Structural Symmetry

    To assure structural symmetry of the seat, Cantor petitioned for a 
pass/fail limit for rearward seat back rotation of no more than 15 
degrees from its initial seat back orientation (measured in real-time 
during the test) and 10 degrees of differential rearward deflection 
between the left and right sides for oblique impacts. NHTSA is granting 
in part on this issue and seeks comment. In particular, does the 
increased prevalence of dual recliners in the fleet remove any safety 
benefits that may be gained from a structural symmetry requirement? If 
not, what test procedures and anti-twisting standards should NHTSA 
consider and why? NHTSA notes that Cantor does not provide data or 
evidence supporting his proposed pass/fail limit or deflection amounts 
proposed.

(c) Dynamic Rear Impact Test Design

    Both Saczalski and Cantor petitioned NHTSA to add a new dynamic 
crash test to FMVSS No. 207, which would test seat back performance 
using a 1,368 kg (3,015 lb) deformable barrier that strikes the rear of 
the vehicle at 80 km/h.\145\ NHTSA is granting the petitions in part on 
this issue and seeks comment on the analysis below. NHTSA has 
previously considered, in the 1974 NPRM, adding a new dynamic 
requirement of the type recommended by Saczalski and Cantor. Table V.2 
shows the various dynamic rear impact tests that have been proposed and 
considered in the past.
---------------------------------------------------------------------------

    \145\ This barrier test would be similar to the barrier test 
that NHTSA included in its latest revision of the FMVSS No. 301; see 
68 FR 67068 (Dec. 1, 2003).

[[Page 58023]]



                                      Table V.2--Past Recommendations for a Dynamic Seat Back Strength Requirement
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                    Saczalski 1989                                       Saczalski 2015
                                   Nash 1974         NPRM 1974            \1\         Cantor 1999 \2\     Viano 2002          \4\          Cantor 2015
--------------------------------------------------------------------------------------------------------------------------------------------------------
Test type....................  FMVSS No. 301     FMVSS No. 301     FMVSS No. 301     FMVSS No. 301     Sled test......  FMVSS No. 301    FMVSS No. 301
                                (1974).           (1974).           (1974).           (1974).                            (2003).          (2003).
Impactor speed \3\...........  48 km/h.........  48 km/h.........  48 km/h.........  48 km/h.........  30-36 km/h\3\..  80 km/h........  80 km/h.
Barrier specs................  1814 kg rigid...  1814 kg rigid...  1814 kg rigid...  1814 kg rigid...  ...............  1368 kg          1368 kg
                                                                                                                         deformable.      deformable.
Impact angle.................  +/- 30 deg......  0 deg...........  0 deg...........  0 deg...........  0 deg..........  0 deg..........  +/- 30 deg.
Impact overlap...............  100%............  100%............  100%............  100%............  100%...........  70%............  70%.
Dummy size...................  HII-50M.........  HII-50M.........  HIII-95M........  50M2............  HIII-50M.......  HIII-95M.......  HIII-50M.
Rear seat dummy..............  ................  ................  ................  ................  ...............  CRABI-12M in     ...............
                                                                                                                         FFCS.
Seat back rotation, max......  No fail.........  40 deg..........  40 deg..........  15 deg..........  35 deg.........  25 deg.........  15 deg.
Seat back twist, max.........  ................  ................  ................  ................  8 deg..........  ...............  10 deg.
Head, HIC....................  ................  ................  ................  unspecified       ...............  CRABI 390        ...............
                                                                                      value.                             [verbar] HIII
                                                                                                                         700.
Head/neck extension..........  45 deg..........  ................  ................  ................  45 deg.........  n/a............  10 deg.
Neck moment..................  45 deg..........  ................  ................  unspecified       20 Nm..........  CRABI 17 Nm      ...............
                                                                                      value.                             [verbar] HIII
                                                                                                                         179 Nm.
Neck x-displacement..........  ................  ................  ................  ................  60 mm..........  n/a............  ...............
Neck y-displacement..........  ................  ................  ................  ................  30 mm..........  n/a............  ...............
Chest deflection.............  ................  ................  ................  ................  ...............  CRABI 30 mm      ...............
                                                                                                                         [verbar] HIII
                                                                                                                         70 mm.
Femur load...................  ................  ................  ................  ................  ...............  CRABI n/a        ...............
                                                                                                                         [verbar] HIII
                                                                                                                         12.7 kN.
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Contained within Saczalski's comments to NHTSA's 1989 Request for Comments. See Regulations.gov, Docket Document No. NHTSA-1996-1817-0024.
\2\ Contained within Cantor's presentation to NHTSA on November 18, 1999. Cantor recommended the use of a dummy designed with an articulated pelvis. See
  Regulations.gov, Docket Document No. NHTSA-1998-4064-0030 for a copy of the presentation.
\3\ Except for the Viano (2003) recommendation, the impactor speed for each recommendation represents the speed of the moving barrier when it strikes
  the stationary test vehicle. The Delta-V experienced by the test vehicle is about half of the impactor speed, depending on the mass of the vehicle.
  For the Viano recommendation, the 30-36 km/h impulse for the sled test corresponds to the Delta-V range observed in FMVSS No. 301 rigid barrier tests
  run at 54.2 km/h (33.2 mph).
\4\ Saczalski's 2015 petition recommended use of ``NHTSA injury reference values for the head, neck, chest, and extremities'' for the HIII-95 seated in
  the front and the CRABI seated in the rear. For convenience, we have entered IARVs for the CRABI ``C'' and the HIII-95M ``H'' in the table above that
  correspond to those that NHTSA recommended in Eppinger, 2000 (cited earlier)

(1) The Saczalski Petition
    In his petition, Saczalski states that a dynamic test is needed, 
but he does not explain the reason that he recommends using a 
deformable barrier travelling at 80 km/h, a HIII-95M in the front seat, 
and a rear seated CRABI in a forward-facing child restraint.
    NHTSA believes that his recommendations are intended to represent 
the crash Saczalski studied in his 2014 FISITA paper, a real-world 
crash that involved an infant fatality in the rear seat.\146\ For the 
paper, Saczalski reconstructed the crash by staging a crash test on the 
same vehicle model (a 2004 Chrysler minivan) with a CRABI dummy in the 
child restraint and an HIII-95M in the front seat. A crash pulse 
generating a [Delta]V of 40 km/h was applied. The test resulted in seat 
back yielding and head-to-head contact between the two dummies. This 
produced a head injury criteria (HIC) of 3192 in the CRABI dummy, which 
is well above the reference value of HIC = 390.
---------------------------------------------------------------------------

    \146\ The crash Saczalski describes in a forward-facing child 
restraint, and a rearward [Delta]V of 40 km/h. (Note: [Delta]V is 
the change in velocity of a vehicle due to a crash or impulse. In 
this instance, the 80 km/h barrier impact with a stationary vehicle 
resulted in a [Delta]V of 40 km/h.)
---------------------------------------------------------------------------

    Saczalski then re-ran the test but replaced the minivan's standard 
front seat with a stronger seat removed from a 2004 Chrysler 
convertible. This was a belt integrated seat design, where the torso 
belt anchorage was attached to the seat back. For such a seat design, 
the seat back attachment to the seat base must be much stronger than a 
typical design because it must be capable of sustaining the seat belt 
loading from frontal crashes. According to Saczalski, the replacement 
seat did not yield significantly in the crash, resulting in no head-to-
head contact and a very low (HIC=36) HIC value of the CRABI dummy. In 
addition, Saczalski presented a process by which he was able to develop 
a predictive equation for determining HIC in the CRABI dummy as a 
function of the front seat occupant mass and the impulse of the crash 
([Delta]V), which involved running slight variations of the above-
described scenario multiple times using the same model of 2004 Chrysler 
minivan. Based on Saczalski's findings, to avoid occupant to occupant 
interaction in the particular crash he studied, the seat back of the 
front seat would need to be strong enough to not excessively yield in a 
crash that involves a [Delta]V of 40 km/h when the seat is occupied by 
a HIII-95M dummy.
    Saczalski's analysis in his FISITA paper is informative, but 
insufficient to support a final rule implementing the test parameters 
utilized and suggested in his petition. First, it is based on tests of 
only a single vehicle model (a 2004 Chrysler minivan), two seat 
designs, and a single child restraint system (CRS) model. Additional 
data from a wider variety of vehicles, seats, and CRS models would be 
needed to determine whether Saczalski's findings in his FISITA paper 
are consistent across the U.S. fleet of passenger cars. Of particular 
concern is the fact that the belt integrated seat design used as an 
acceptably performing seat is relatively rare in the fleet (primarily 
used in convertibles) and designed for seat belt loading in the frontal 
direction.\147\
---------------------------------------------------------------------------

    \147\ 2016-2016 estimates put convertible sales at approximately 
1.9% in the U.S. Source: https://www.iseecars.com/most-convertibles-by-state-2017-study.
---------------------------------------------------------------------------

    Second, the tests use a front seat test dummy, the HIII-95M, which 
is not a regulated test tool and may not have the full scope of 
necessary traits for rear impact testing at high speed. In particular, 
the HIC response generated by the dummy may be of limited value for 
analyzing the situation in question because the rear part of the 
dummy's

[[Page 58024]]

head, which contacts the child dummy, is not designed to provide an 
internal or external biofidelic impact.
    Third, the predictive HIC equation on which Saczalski based his 
recommended test setup does not use adequate statistical methods. It is 
generated using only five data points, potentially making it 
insufficiently robust. Moreover, it bases the prediction through two of 
the more extreme data points, while ignoring the other three. As a 
result, the predictive function fits the two selected points perfectly, 
but very poorly fits the others. Finally, because standard regression 
techniques were not applied, there were no statistical computations of 
standard errors or other measures of fit, such as R-squared. Given 
these shortcomings, NHTSA does not believe it could base its selection 
of test parameters in a new dynamic seat back strength test on 
Saczalski's data. NHTSA seeks comment on this analysis and whether 
there is additional supporting data for Saczalski's proposed test 
design.
(2) The Cantor Petition
    Cantor similarly does not provide support for the test parameters 
he chose in his recommendation for a dynamic rear-impact seat back 
strength test. He argues that because the impulse created by the 80 km/
h barrier is appropriate for the FMVSS No. 301 fuel system integrity 
standard, it would also be appropriate for setting a minimum seat back 
requirement. This is a generalization that requires further 
justification. Because the minimum requirements for seat back strength 
and fuel system integrity do not address the same safety concerns, 
NHTSA believes this is insufficient basis, on its own, to implement 
this test parameters.
    Finally, NHTSA would need to show that any dummy used in a new 
dynamic test is chosen appropriately. The petitioners suggested the use 
of a Hybrid III dummy (HIII-95M by Saczalski; HIII-50M by Cantor). As 
stated, in regard to Saczalski's 2014 FISITA paper, the Hybrid III 
dummies have significant biofidelity limitations when used for rear 
impact analysis. NHTSA seeks comment on whether there is evidence 
showing these limitations are acceptable and would lead to appropriate 
seat designs if these dummies are chosen for a new dynamic test in 
FMVSS No. 207.
2. Matters on Which NHTSA Is Denying the Petitions
(a) Incorporate a Cargo Stipulation Into FMVSS No. 207
    Saczalski requested that NHTSA amend FMVSS No. 207 to include a 
cargo stipulation in a dynamic vehicle test. Saczalski argued that 
deformation of the rear of the vehicle caused by crash forces could 
cause loose cargo stored in the rear (or trunk) to be pushed forward 
into the back of the second row of seats, causing those seats and their 
occupants to in turn be pushed forward into the back of the front row 
seats.
    NHTSA previously denied a similar request from Cantor in 2004, and 
Saczalski did not provide additional field data or analysis to support 
adding specifications for cargo placement.\148\ Without further 
analysis, NHTSA is not considering incorporating a cargo stipulation in 
FMVSS No. 207 at this time. This decision will allow NHTSA to focus its 
resources more fully on the aspects of the petitions related to 
rearward seat back strength.
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    \148\ Cantor sought inclusion of an unrestrained cargo test for 
the safety of occupants in the rear seat. 71 FR 70477 (Dec. 5, 
2006). 71 FR 70478. NHTSA denied that petition because the incidence 
of injuries caused by loose luggage was very low and did not warrant 
an amendment to a Federal safety standard, and Cantor did not 
provide any field data demonstrating a correlation between cargo 
intrusion and occupant safety.
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(b) Amend FMVSS No. 209 To Require That Seat Belts Remain on Pelvis 
Under All Conditions
    Cantor requested NHTSA restore language, previously deleted in 
1999, in FMVSS No. 209 requiring that the pelvic restraint portion of 
both Type-1 and Type-2 seat belts remain on the pelvis under all 
conditions.\149\ NHTSA is denying this request.
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    \149\ The paragraph in question, S4.1(b), read as follows: 
``4.1(b) Pelvic restraint. A seat belt assembly shall provide pelvic 
restraint whether or not upper torso restraint is provided, and the 
pelvic restraint shall be designed to remain on the pelvis under all 
conditions, including collision or roll-over of the motor vehicle. 
Pelvic restraint of a Type 2 seat belt assembly that can be used 
without upper torso restraint shall comply with requirement for Type 
1 seat belt assembly in S4.1 to S4.4.''
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    Cantor states that restoration of this paragraph will prevent 
ramping by assuring that manufacturers install a device that keeps the 
lap belt portion of the seat belt on the pelvis under all crash 
conditions. According to Cantor, technology that would prevent ramping 
is already available on the market, including the following: a sliding/
cinching latch plate to prevent excess shoulder belt webbing from 
transitioning to the lap belt portion and causing the lap belt to go 
slack; an integrated seat in which both lap and shoulder belt anchors 
are mounted to the seat; and seat belt pretensioners sensitive to rear 
impacts and designed to work with an integrated seat with a belt 
configuration as described above.
    The agency removed this stipulation from the standard in 1999 
because it was deemed redundant and unnecessary.\150\ FMVSS No. 208, 
other provisions in FMVSS No. 209, and FMVSS No. 210 contained more 
specific requirements that collectively have the effect of requiring 
pelvic restraint and thereby reducing the likelihood of occupants 
submarining \151\ during a crash. It was also deemed unenforceable 
because the regulation did not provide an objective means to determine 
that a lap belt complied with the requirement and was in fact 
``designed'' to remain on the pelvis. In addition, NHTSA noted that the 
meaning of the words, ``remain on the pelvis,'' was unclear. Because 
these conditions and reasons have not changed since that action was 
taken, NHTSA will not reinstate the requested language.
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    \150\ 64 FR 27203 (May 19, 1999).
    \151\ ``Submarining'' refers to the tendency for a restrained 
occupant to slide forward feet first under the lap belt during a 
vehicle crash, which could result in serious abdominal, pelvic, and 
spinal injuries.
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(c) Add a Rear Impact Test to FMVSS No. 213, Child Restraint Systems
    Saczalski requested that NHTSA revise FMVSS No. 213 by including a 
rear impact requirement for child restraint systems like the one 
described in ECE Reg. No. 44. Saczalski's only change from Reg. No. 44 
is performing the rear impact test at a 40 km/h velocity instead of 30 
km/h. Saczalski stated that such a revision is necessary to prevent 
rear facing child restraint systems (CRSs) from folding rearward when 
they become trapped between a rear seat and a yielding front seat back 
during a rear impact crash.\152\
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    \152\ This condition was highlighted in Saczalski's 2014 FISITA 
paper.
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    NHTSA is denying this request for change. NHTSA considered adopting 
ECE Reg. No. 44's rear impact test into FMVSS No. 213 in the past.\153\ 
In a 2002 ANPRM, NHTSA discussed agency tests evaluating ECE Reg. No. 
44's rear impact test conducted at 30 km/h (18.6 miles per hour), with 
peak deceleration between 14 g and 21 g over a 70-millisecond time 
period. The tests were dynamic sled testing performed by NHTSA in 
research on FMVSS No. 202 and FMVSS No. 207, where NHTSA added a rear-
facing child restraint with a 12-month-old test dummy to a 1999 Dodge 
Intrepid vehicle seat. One test, simulating a dynamic FMVSS No. 202

[[Page 58025]]

condition, was conducted at approximately 17.5 km/h (11 mph). The other 
two tests were conducted at approximately 30.5 km/h (19 mph). In all of 
the tests the 12-month-old dummy in the rear-facing child restraint was 
able to easily meet the injury criteria of FMVSS No. 208, i.e. was 
below the threshold for injury. After examining these data, comments to 
the ANPRM, and data showing that fatalities for children in rear impact 
crashes constitute a much smaller percentage of the total than other 
crash modes, NHTSA decided to focus its resources on developing a side 
impact test and not a rear impact test.\154\
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    \153\ NHTSA analyzed this issue in a rulemaking amending FMVSS 
No. 213 pursuant to the Transportation Recall Enhancement, 
Accountability and Document Act (TREAD Act), November 1, 2000, 
Public Law 106-414, 114 Stat. 1800. The agency requested comments on 
the merits of incorporating the rear impact test of ECE Reg. No. 44 
into FMVSS No. 213 (ANPRM; 67 FR 21836, 21851 (May 1, 2002)).
    \154\ NHTSA withdrew the rulemaking in a final rule, 68 FR 
37620, 37624 (June 24, 2003). See also Report to Congress, ``Child 
Restraint Systems, Transportation Recall Enhancement, Accountability 
and Document Act,'' February 2004. chrome-extension://
efaidnbmnnnibpcajpcglclefindmkaj/https://www.nhtsa.gov/sites/nhtsa.gov/files/documents/tread.pdf.
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    NHTSA disagrees with Saczalski that there is a need to adopt a 40 
km/h rearward impact test based on ECE Reg. No. 44. NHTSA does not 
believe adopting such a rear impact test is warranted for a number of 
reasons. First, rear impact fatalities among children restrained in 
CRSs are generally in very severe crashes that result in significant 
passenger compartment intrusion into the rear seating area. However, 
the ECE Reg. No. 44 sled test requested by the petitioner does not 
simulate such intrusion into the seating area. Second, the ECE test 
protocol does not evaluate the circumstance about which Saczalski is 
concerned. The rear impact test in ECE Reg. No. 44 does not have a 
simulated front seat and therefore does not replicate the crash 
scenario the petitioner seeks to evaluate. The standard seat assembly 
in FMVSS No. 213 also does not include a simulated front seat, and it 
is yet to be determined if a representative front seat could be 
designed and whether it could be made to collapse in a compliance test 
in a repeatable and reproducible manner.
    Finally, the petitioner provides no information about a practicable 
countermeasure that CRSs can provide that would prevent injuries and 
fatalities if there is a front seat collapse and/or intrusion into the 
rear seating area. NHTSA undertakes rulemakings on FMVSS No. 213 
weighing various principles and considerations, in addition to the 
considerations and requirements for FMVSS specified by the Safety Act, 
statutory mandates, Executive Order (E.O.) 12866,\155\ and other 
requirements for agency rulemaking. In making regulatory decisions on 
possible enhancements to FMVSS No. 213, NHTSA considers the consumer 
acceptance of cost increases to an already highly effective item of 
safety equipment and whether an amendment could potentially have an 
adverse effect on the sales of this product. The net effect on safety 
could be negative if CRSs are not used as much because of cost 
increases. NHTSA also weighs the effects of an amendment on the ease of 
correctly using child restraints. We consider whether an amendment may 
cause child restraints to become overly complex or frustrating for 
caregivers, resulting in increased misuse or nonuse of the restraints. 
The petitioner did not provide information that would enable NHTSA to 
assess these practicability issues.
---------------------------------------------------------------------------

    \155\ E.O. 12866, ``Regulatory Planning and Review,'' September 
30, 1993, as amended by E.O. 14094.
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    Based on the forgoing, NHTSA is denying Saczalski's request to 
amend FMVSS No. 213.
(d) NCAP Implementation
    Cantor requested that NHTSA implement a rear-impact crash test into 
the 5-star rating as part of his dual FMVSS/NCAP approach. NHTSA's 
regulations at 49 CFR 552.3 state that a petition for rulemaking may be 
filed respecting the issuance, amendment or revocation of a motor 
vehicle safety standard. NCAP is not a motor vehicle safety standard. 
Therefore, a petition for rulemaking is not the appropriate mechanism 
for requests to amend the NCAP program. NHTSA therefore denies Cantor's 
petition for rulemaking. After NHTSA's planned research is completed, 
however, we will be in a better position to consider how best to 
implement any necessary changes both in our standards and/or NCAP.

F. Conclusion of NHTSA Assessment of Cantor and Saczalski Petitions

    In accordance with 49 CFR part 552 and after careful consideration, 
Cantor's request to restore pelvic restraint language to FMVSS No. 209, 
and Saczalski's request to add a rear impact test to FMVSS No. 213 and 
to add a cargo test and requirement to FMVSS No. 207 are denied based 
on the information presented above. This ANPRM provides the required 
notification of the denial. As part of our effort to facilitate further 
research and data development to support a potential rulemaking to 
updated FMVSS No. 207, NHTSA grants in part both petitions regarding 
updating the moment strength requirement in FMVSS No. 207 and the 
development of updated static and dynamic test procedures for seat back 
strength, and Cantor's petitioned-for request on structural symmetry. 
NHTSA seeks comment on the issues discussed above.

G. Center for Auto Safety (CAS) Petition

    On March 9, 2016, CAS petitioned NHTSA to amend FMVSS No. 208 and 
FMVSS No. 213 to require additional warnings instructing parents to 
place children in rear seating positions behind unoccupied front seats, 
if possible, or behind the lightest front seat occupant.
    CAS requested that FMVSS No. 208, S4.5.1(f), be amended so that the 
vehicle owner's manuals be required to include the following language 
(or similar):
    ``If possible, Children Should Be Placed in Rear Seating Positions 
Behind Unoccupied Front Seats. In Rear-End Crashes, the Backs of 
Occupied Front Seats Are Prone to Collapse Under the Weight of Their 
Occupants. If This Occurs, the Seat Backs and Their Occupants Can 
Strike Children in Rear Seats and Cause Severe or Fatal Injuries.''
    CAS also requested that the label found at FMVSS No. 213, Figure 
10, be amended to include the statement ``Place behind an unoccupied 
front seat where possible.''

H. Analysis of CAS Petition

    CAS requested that NHTSA add warning statements in the owner's 
manual and on CRS labels to warn parents to ``Place behind an 
unoccupied front seat where possible.'' Currently, the CRS label warns 
of the potential injury that could result from placing a CRS in front 
of an air bag but does not make any statement relating to where else in 
the vehicle the CRS should not be placed. Moreover, the CRS label 
instructs that ``The back seat is the safest place for children 12 and 
under.'' \156\
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    \156\ FMVSS No. 213, Figure 10.
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    CAS does not provide analysis demonstrating a net benefit to 
placing the child in a specific rear seat. Long established data show 
that the rear seat is the safest place for children under the age of 
13.\157\ Published NHTSA data shows that rear seats are 25-75 percent 
more effective in reducing fatalities (compared to front seats) for 
children 0-12 years old.\158\ However, the overall risk to CRS-seated 
children in each rear position depends on many factors other than front 
seat occupancy. These factors may include which side of the vehicle

[[Page 58026]]

is struck in a side impact (and where the CRS is placed in relation to 
that impact) and the risks involved in more common frontal impacts. CAS 
fails to provide sufficient data or other information to conclude that 
the warning recommended in its petition would have any net benefit.
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    \157\ Braver, ER et al. Seating positions and children's risk of 
dying in motor vehicle crashes. Inj Prev. 1998;4:181-187. Durbin, DR 
et al. Effects of seating position and appropriate restraint use on 
the risk of injury to children in motor vehicle crashes. Pediatrics. 
2005;115:e305-e309.
    \158\ Kuppa, S et al. Rear Seat Occupant Protection in Frontal 
Crashes. 2005 Enhanced Safety of Vehicles Conference, Paper No. 05-
0212.
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    By contrast, there may be unintended safety harms that such a label 
could generate. The suggested label could dilute the message about the 
importance of placing children in the rear seat. It could be read by 
some consumers as inconsistent with the label required by Figure 10 of 
FMVSS No. 213 that the rear seat is the safest place for children aged 
12 and under. Such inconsistency may confuse them and reduce the 
efficacy of the current CRS label. The label could lead some caregivers 
to install the child restraint system in a front seating position 
rather than a rear seating position to avoid rear proximity to an 
occupied front seat. This outcome could have severe consequences if the 
rear-facing CRS were positioned in front of a deploying air bag. 
Another unsafe outcome of such confusion could be some caregivers 
deciding not to use a CRS at all with their child when the CRS cannot 
be placed behind an unoccupied front seat. CAS did not provide any 
assessment of the risk of unintended consequences related to the 
petition for a label. The guidance recommended by CAS may result in the 
continual removal and reinstallation of a CRS by parents, depending on 
front seat occupancy, as they decide which seating position is safer. 
Such actions could lead to fatigue, with some caregivers eventually 
ignoring the instruction. Not only would that undermine the label's 
purpose, but NHTSA is also concerned that caregivers may start to 
ignore other instructions and warnings on the label, such as the 
warning on the label required by Figure 10 not to place the CRS on the 
front seat with an air bag. Such a warning is crucial to the safety of 
the child and must be always followed.
    Finally, NHTSA rejects CAS's request to add language to FMVSS No. 
208, S4.5.1(f) and therefore required in owner's manuals, stating ``If 
possible, Children Should Be Placed in Rear Seating Positions Behind 
Unoccupied Front Seats. In Rear-End Crashes, the Backs of Occupied 
Front Seats Are Prone to Collapse Under the Weight of Their Occupants. 
If This Occurs, the Seat Backs and Their Occupants Can Strike Children 
in Rear Seats and Cause Severe or Fatal Injuries.'' We are denying this 
request for the same reasons discussed above, namely that CAS has not 
provided supporting information demonstrating the benefit of the change 
and has not provided analysis of unintended consequences that the 
amendment may cause. We also emphasize that this language proposed for 
the owner's manual, by focusing even more on the risk of seat back 
collapse than the language proposed for the label, has added potential 
to cause confusion beyond the language petitioned for the label. 
Therefore, NHTSA will not incorporate the requested amendment.
    For these reasons, NHTSA does not believe adopting CAS's 
recommendation to change the CRS label or amend FMVSS No. 208, 
S4.5.1(f) would be appropriate. The agency continues to promote the 
message that the rear seat is the safest place for children. In 
accordance with 49 CFR part 552 and after careful consideration, the 
CAS petition for a labeling requirement to be added to FMVSS No. 213 
and to amend FMVSS No. 208 is denied based on the information presented 
above. This ANPRM provides the required notification of the denial.

VI. Unified Approach to Rear Impact Protection

A. Introduction

    As NHTSA undertakes this process, our main considerations, as 
always, are safety and the obligations the agency has under the Vehicle 
Safety Act. IIJA requires that we publish this ANPRM to update FMVSS 
No. 207. Throughout this rulemaking effort, we need to take into 
account the Safety Act's imperative that FMVSS be practicable, meet the 
need for motor vehicle safety, and be stated in objective terms. The 
long-term and ongoing challenge to meeting these goals has been to 
develop an update to FMVSS No. 207 and rear impact protection in 
general that effectively balances the tradeoffs to improve overall 
safety with a reasoned consideration of all factors involved. As far 
back as 1974, NHTSA understood that there would be advantages in taking 
a more unified approach to rear impact protection. The 1974 NPRM 
preamble stated that consolidation of Standards 202 and 207 logically 
reflects the relationship of the seat and its head restraint and would 
improve the possibilities of eventually testing the whole seating 
system with a dynamic test procedure.
    In 1992, the agency again signaled that it continued to believe 
that a unified approach was likely the best approach to rear impact 
protection. In that report, the agency stated that there are four 
categories of performance issues that need to be addressed as part of 
future changes to FMVSS No. 207. These four categories are: (1) Seating 
system integrity; (2) Seat energy absorbing capability; (3) 
Compatibility of a seat and its head restraint; and (4) Seat and seat 
belt working together. In the 2004 final rule to update FMVSS No. 202, 
NHTSA again reiterated the ultimate goal of adopting a method of 
comprehensively evaluating the seating system.
    The four rear impact protection categories outlined in 1992 
indicate the need to maintain a balance between energy absorbing and 
stiffness characteristics and the fact that the severity and type of 
occupant injuries varies with impact velocity in rear collisions. Low-
to-moderate velocity crashes represent the majority of rear collisions, 
and these crashes are responsible for the majority of reported 
injuries, mainly whiplash. At higher impact velocities the injury risks 
for the occupant of a seat include bodily impact with vehicular 
structures, severe thorax, pelvis, and neck injuries, and other 
risks.\159\ Additionally, at higher impact velocities deformation of 
the seat sufficient to allow interaction between front and rear 
occupant rows and associated injuries can occur. The debate around 
FMVSS Nos. 202a and 207 concerns how effective these standards are in 
mitigating these risks and the inevitable tradeoffs.
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    \159\ We note that 2017-2020 CISS data indicates that at all 
rear impact crash speeds whiplash remains more frequent than any 
MAIS 2+ injury.
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    NHTSA seeks comment broadly on an update to the FMVSS regarding 
occupant protection in rear impacts. Even if it has been clear for many 
years that the ideal approach to rear impact safety would incorporate 
consideration of both moderate and severe rear impacts, is there a 
sound scientific basis for a reasonable update to the standards for 
rear impact protection and are the necessary technical tools available 
for a sound rulemaking proposal? Can we have a high degree of 
confidence that any such proposal will be generally beneficial? In the 
following section, we further analyze, discuss, and seek comment on 
potential paths forward for an update to rear impact protection 
required by the FMVSSs, with emphasis on a unified approach.

B. FMVSS No. 207

    Generally, the discussion around FMVSS No. 207 has been a narrow 
focus on seat back strength. However, occupant protection in rear 
impact involves many other issues. Some, such as Prasad in 1997 and 
Burnett in 2004,

[[Page 58027]]

suggested that seat back strength has limited correlation with occupant 
dynamics prior to seat back failure. Such conclusions, however, were 
drawn from older designs whose seat strength is much lower than some 
have proposed for a FMVSS No. 207 upgrade.\160\ Nonetheless, in its 
present form, the standard provides limited guarantees on how an 
occupant will respond to a rear collision prior to the seat back 
failing. In fact, the FMVSS No. 202a requirements likely have a greater 
influence on occupant protection because the majority of rear 
collisions yield minor or no injuries and occur at relatively low 
[Delta]Vs. For example, table II.3 shows NHTSA's estimate that in rear 
collisions, 96% of injuries were MAIS 1-2 and, if [Delta]V was known, 
76% of MAIS 1-2 injuries occurred at [Delta]V of 30 km/h or less. 
Therefore, the present scope of FMVSS No. 207 is limited in the sense 
that it focuses only on the first category of the four seat performance 
categories for rear impact protection, i.e., seating system integrity.
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    \160\ See table VI.1, above.
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    Furthermore, a very high seat back strength requirement in FMVSS 
No. 207 would likely result in a seat back with very high stiffness due 
to the necessary structural reinforcements. Such seats may impose high 
occupant loading due to rapid acceleration in higher speed rear 
impacts.\161\ However, whether such loading is necessarily injurious, 
the speeds at which such loading may be injurious, and whether the 
trade-offs between stiffness and injury are inherent or can be 
compensated for in other design elements, are all matters to be 
considered. On the other hand, a seat back with very low strength may 
quickly reach a rotation limit, or fail, at lower rear impact speeds.
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    \161\ The reader is referred to the increased risks as noted in 
the 1997 Prasad study and concerns drawn out from the 1989 Request 
for Comments. We note, however, that these conclusions are based on 
seats that are now decades old. A more recent examination of this 
can be found in 2023 Kang, for a very severe rear impact condition 
and a rigid seat structure.
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    In striking this balance, manufacturers have, in general, settled 
on seat back strength that has increased on average over the decades to 
many times the value set by FMVSS No. 207.\162\ Viano, et al., for 
example, noted that MY 1990s dual recliner seats had an average peak 
moment strength of 1,970 Nm while MY 2000s era dual recliner seats had 
an average peak moment strength of 2,360 Nm.\163\ As noted in the 2019 
Edwards study,\164\ it appears as if some manufacturers have strived to 
achieve balance in modern seating systems between low-speed whiplash 
protection and structural integrity at higher speeds.
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    \162\ Saunders, J., Molino, L.N., Kuppa, S., and McKoy, F.L. 
Performance of seating systems in a FMVSS No. 301 rear impact crash 
test. Proceedings of 18th International Technical Conference on the 
Enhanced Safety of Vehicles, 2003. Nagoya, Japan.
    \163\ Viano, David C., et al. ``Occupant responses in 
conventional and ABTS seats in high-speed rear sled tests.'' Traffic 
injury prevention 19.1 (2018): 54-59.
    \164\ Edwards, Marcy A., et al. ``Seat design characteristics 
affecting occupant safety in low-and high-severity rear-impact 
collisions.'' IRCOBI Conference, Florence, Italy, IRC-19-11. 2019.
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    Currently, FMVSS No. 207 addresses a segment of the overall rear 
impact protection issue. In addition, the regulated seat strength set 
by FMVSS No. 207 is considerably lower than the average seat strength 
of modern production seats. The following section outlines different 
approaches for updating the standard to enhance or broaden the scope of 
rear impact protection, thereby further addressing the rear impact 
protection points set by NHTSA.

C. Analysis of Approaches To Updating Standards for Occupant Protection 
in Rear Impact

1. Seat Back Strength and Other Mechanical Properties
    A foundational consideration for updating standards related to rear 
impact protection is the strength of cantilevered seat backs in the 
rearward direction, regardless of how the seat back strength is tested 
or measured. The current strength level set by FMVSS No. 207 is far 
below the average design strength of production seats. As a result, 
manufacturers have great flexibility in seat back design. This 
flexibility allows manufacturers to readily adopt new technology such 
as active head restraints, and to allow their seat designs to quickly 
evolve as the understanding of rear impact protection changes. Any 
increase in the seat back strength requirement will reduce manufacturer 
flexibility. Furthermore, any new strength requirement should reduce 
injuries and adequately balance tradeoffs. As with any other regulatory 
change, due consideration must be given to overall cost effectiveness 
of proposed changes to the regulatory regime.
    As a starting point, the required level of seat back strength 
should limit the interaction between the occupants of different rows of 
seats in a rear impact. It is not clear, however, what level of crash 
severity is sufficient to protect against and for what size of 
occupant. No seat strength requirement can protect all occupants in all 
possible rear impact severities, but the selected strength should 
attempt to be protective of as many occupants as possible within the 
constraints of practicality and cost. Therefore, we seek comment on the 
correct minimum seat back strength requirement. We further seek comment 
on ways this parameter can be tested and measured. We also seek comment 
on the benefits or harm generated by the manufacturer flexibility 
allowed by a low minimum seat back strength requirement, and how NHTSA 
should understand those benefits or harms as well as the cost to 
manufacturers to comply with alternative elevated lower bound seat back 
strength options.
    Another issue is energy absorption. The energy absorption or force-
deflection characteristics of seat backs are currently not regulated by 
FMVSS No. 207. Controlled deformation of the seat back allows the 
occupant of a seat to ride-down a crash in a manner that may minimize 
injury. However, if the seat back absorbs the crash energy elastically 
rather than irreversibly,\165\ there may potentially be injurious 
rebound of the occupant. Thus, remaining residual energy after occupant 
ride-down may be an important consideration. We note that FMVSS No. 222 
incorporates a rearward energy absorption and force deflection 
requirement for school bus seat backs. We seek comment on whether a 
similar requirement should be incorporated into FMVSS No. 207 and what 
the performance level should be.
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    \165\ When the seat back deforms elastically it absorbs energy 
like a spring and will return to its original position and shape 
after the applied force is removed. When the applied force is 
sufficient to cause yielding in the seat back there is irreversible, 
also termed inelastic or plastic, deformation in the seat back which 
permanently absorbs some energy; in which case the seat back will 
not return to its original position and shape after the applied 
force is removed.
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    Older seat designs have typically used a single recliner mechanism 
to control seat back rotation. Because of the nature of such a design, 
rearward seat back load is not uniformly restricted, leading to one 
side of the seat back rotating more than the other; this lack of 
structural symmetry may lead to a subsequent twisting of the seat back. 
It has been theorized that such twisting reduces the ability of the 
seat back to prevent occupant ramping. Both of the current petitions 
discussed earlier in this ANPRM desired some limit to be placed on seat 
twist. We seek comment on whether a similar requirement is needed, what 
the performance level should be and how it should be measured.
    We also seek comment on whether an updated FMVSS should regulate 
other seat characteristics that may be related

[[Page 58028]]

to occupant ramping, such as pocketing and the coefficient of friction 
of the upholstery. We also seek comment on any other seat 
characteristics that should be regulated for rear impact protection.
2. Test Parameters
    This section discusses and requests comment on means of testing or 
measuring seat parameters. We first discuss the benefits and 
limitations of a quasi-static approach. Afterward, we discuss and seek 
comment on a dynamic testing regime that utilizes two testing speeds to 
cover the variety of rear impact occupant protection scenarios.
3. Quasi-Static Testing
    One approach to update FMVSS No. 207 is to increase the required 
seat back moment while retaining the current test procedure of loading 
the upper frame member or some other part of the seat back. This is 
appealing in its simplicity but has some potential shortcomings. First, 
the required moment is specified to be applied through a horizontal 
force and a distance from the seating reference point. This works well 
as an initial condition and within the required moment value, which 
typically results in a relatively small amount of seat back rotation. 
Depending on the increase in moment value, however, significant seat 
back deformation could occur during testing. In this circumstance, 
maintaining a horizontal load throughout the test becomes a serious 
challenge.
    In addition, it is not clear that loading the seat back at the 
upper crossmember is the best way to quasi-statically load the seat 
back. Over the years, several different methods of loading the seat 
back have been developed that may better achieve the goals of the 
test.\166\ For example, NHTSA has tested seat backs to failure by 
modifying the FMVSS No. 207 procedure such that the loading arm rotates 
with the seat back and the initial direction of loading perpendicular 
to the seat back as specified by SAE J879.\167\ Some methods involve 
the use of body-blocks or counter balanced ATDs, pushed or pulled into 
the seat back, which loads the seat back in a manner more closely 
related to how a human may load the seat back. Such methods can also 
measure force-deflection in addition to strength.
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    \166\ Burnett, R; Viano, D; Parenteau, C; (2022) ``Quasi-Static 
Methods to Evaluate Seat Strength in Rear Impacts.'' Traffic Injury 
Prevention.
    \167\ Molino, L (1998): Determination of Moment-Deflection 
Characteristics of Automobile Seat Backs. NHTSA Technical Report, 
DOT Docket Management System NHTSA-1998-4064.
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    However, existing quasi-static test procedures are also limited 
because they can tell us how the seat reacts when it is loaded, but 
they cannot tell us whether the seat's characteristics are potentially 
injurious to or protective of the occupant in certain rear impacts. 
Thus, the value of the quasi-static method may be limited if the 
relationship between mechanical seat properties and occupant response 
in a rear impact is not well understood. This may lead to a lack of 
optimization and the potential introduction of harmful seat behavior.
    We seek comment on the use of quasi-static testing in an updated 
rear impact occupant protection regime. Could changes be made to quasi-
static procedures or loading devices that would help discern the effect 
of the seat design on the seat's occupant? Is this important to fully 
understand how changes to seat strength or other seat design parameters 
will affect the occupant prior to determining what level of increase in 
minimum seat back strength is sufficient? Is this information necessary 
to develop objective measures, tests, and strength requirements for 
seat backs?
    The above discussion is primarily related to determining seat back 
performance at higher severity levels. Any unified approach, however, 
must also consider the frequent lower speed rear impacts correlated to 
whiplash injury. Currently, FMVSS No. 202a requires the head restraint 
to have a minimum height and maximum backset or optionally limit the 
head to torso rotation of a Hybrid III dummy in a sled test. What 
changes can be made to the test method and standard for head restraints 
from a quasi-static requirement perspective that may improve the 
protection against whiplash in moderate severity rear impacts and/or 
create more synergistic total rear impact protection?
4. Dynamic Testing
    Considering the limitations of quasi-static testing in an 
environment with significant uncertainty regarding injury dynamics, a 
dynamic assessment of seat behavior at multiple impact severities may 
be a more effective method for achieving a unified and synergistic 
approach to rear impact protection. As noted above, this approach has 
been a feature of past efforts to update standard FMVSS No. 207 and is 
also consistent with the four rear impact protection points. In this 
section, we discuss and seek comment on various dynamic testing 
approaches to achieve the goal of improved rear impact protection. 
Topics of discussion include test speeds, seat performance measures, 
ATD selection, and ATD performance measures.
    To fully assess the four rear impact protection points, NHTSA is 
considering a dynamic approach that contains both a low and high-speed 
test. Each of these regimes place distinct requirements on the seating 
system, and a dual speed regime can help ensure balance in rear impact 
protection. NHTSA believes a two-tiered approach will preserve seat 
design flexibility while improving protection for the occupant across a 
range of rear impact severities.
    NHTSA is considering which ATDs are best suited to use in rear-
impact dynamic testing, at both low and high-speed. A low-speed test 
would assess the seating system's ability to protect against injuries 
to the cervical spine. As mentioned previously, FMVSS No. 202a 
currently includes a low-speed sled test option using the HIII-50M test 
dummy. NHTSA is considering a similar test utilizing the BioRID 50th 
percentile male dummy and believes this dummy provides significant 
improvements over other ATD options. A high-speed test would assess the 
rear impact regime where significant rearward rotation of the seat back 
may occur, and occupant retention becomes a concern as well as contact 
with rear seat occupants. An ATD used for this type of test should have 
characteristics that replicate the interaction of the occupant with the 
seat back. NHTSA is also considering BioRID for use in the higher speed 
test but acknowledges that the two test severities require different 
ATD capabilities. NHTSA is aware of a female rear impact dummy finite 
element model, EvaRID FE, which is a scaled down version of the BioRID, 
with mass and geometrical dimension representing a 50th percentile 
female. The agency is also aware of the development of a prototype 50th 
percentile female rear impact dummy known as the BioRID-P50F,\168\ and 
is also interested in, and seeks comment on, the potential for its use 
and to what extent its state of readiness is consistent with a 
potential rulemaking proposal. The agency seeks comment on which ATDs 
would be most appropriate to use in both low and high-speed rear impact 
testing of seats, and whether using two different sized ATDs (for 
example, BioRID and BioRID-P50F) in one or both of these test 
configurations would

[[Page 58029]]

offer a more comprehensive assessment of seat performance.
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    \168\ The physical BioRID-P50F dummy is currently in prototype 
stage and not available for evaluation by the agency.
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(a) Low-Speed Test
    An upgraded low-speed test would assess the energy absorption 
characteristics and compatibility of the seat and head restraint with 
respect to occupant protection in low severity rear impacts. The 
primary concern in low-speed rear impacts are cervical spine injuries 
associated with whiplash. Therefore, a low-speed test should promote 
best practices that mitigate whiplash beyond what is currently achieved 
by FMVSS No. 202a by ensuring compliance with a standard that 
establishes a minimum level of injury prevention. During the rulemaking 
establishing FMVSS No. 202a, the agency acknowledged commenters' 
criticism of the biofidelity sufficiency of the HIII-50M used in 202a, 
particularly its neck, in the rearward direction.\169\ Thus, it is 
appropriate for the agency to explore the use of alternative ATDs such 
as BioRID, which may more accurately replicates spinal, torso and head 
motion. As discussed below, this comes with challenges in determining 
an acceptable and repeatable biomechanical measurement. Below, we 
discuss and seek comment on certain considerations relevant to a low-
speed test: test pulse and injury criteria and test repeatability.
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    \169\ 69 FR 74873 (Dec. 14, 2004); The agency concluded at that 
time that the HIII-50M was sufficient to discern between acceptably 
safe head restraint systems and those that allow unacceptable levels 
of head-to-torso rotation. Nonetheless, the agency stated it was 
likely ``to revisit the decisions made in [the] final rule about 
dynamic performance values and the test device as more advanced 
dummies are developed and the injury criteria achieve broader 
consensus.''
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    First, we consider the appropriate test pulse. The low-speed regime 
is typically associated with rear impact [Delta]V between 16 and 24 km/
h. The dynamic sled test option in FMVSS No. 202 has a [Delta]V target 
of 17.3  0.6 km/h. The Euro NCAP whiplash assessment uses 
low, medium and high severity sled acceleration corridors with target 
[Delta]Vs of 16.10, 15.65 and 24.45 km/h. The IIHS dynamic whiplash 
rating uses a simulated rear impact conducted on a sled using a 
[Delta]V of 10 mph. In addition to the issues outlined below, NHTSA 
seeks comment on the test pulse for a low-speed rear impact test, such 
as [Delta]V and acceleration profile.
    Next, we consider injury criteria and test repeatability. Current 
low-speed testing practices present challenges with well-defined injury 
criteria and repeatability of the tests. The understanding of whiplash 
injury mechanisms continues to evolve, and contemporary ATD injury 
criteria are therefore derived from nonlinear statistical correlations 
with biomechanical data. Because of this evolving understanding, 
existing dynamic whiplash assessments use a range of ATD measures. For 
example, the 2009 EuroNCAP dynamic whiplash ratings system \170\ 
calculates a rear impact seat performance rating using a combination of 
seven measures from rear impact sled testing using the BioRID ATD. 
These measures are:
---------------------------------------------------------------------------

    \170\ van Ratingen, Michiel, et al. ``The Euro NCAP whiplash 
test.'' 21st international technical conference on the enhanced 
safety of vehicles. 2009.

 NIC (neck injury criteria),
 Nkm (shear force and bending moment),
 Head rebound velocity,
 Fx upper neck shear,
 Fz upper neck axial force,
 T1 acceleration up to head contact, and
 Head restraint contact time

    Any assessment based on a threshold value of these parameters 
should accurately assess the injury risk. To be objective, the ATD 
metrics of a low-speed test should also be based on a fundamental 
understanding of the biomechanical injury mechanisms. For example, NIC 
is based on the principle of neck retraction prior to the head 
contacting the head restraint, described earlier in the Neck injuries 
subsection, leading to injurious pressure waves in the spinal 
canal.\171\ An injury threshold of 15 m\2\/s\2\ for the NIC was 
suggested \172\ after analyzing human volunteer results \173\ to find a 
lower bound of injury tolerance. However, the predictive basis of ATD 
metrics for low-speed injury are usually based on a statistical 
nonlinear analysis of biomechanical data and shows varying degrees of 
success in predicting real world outcomes. In the 2019 Edwards 
study,\174\ the authors compared low-speed BioRID measurements with 
insurance claim data. The standard whiplash metrics, such as those 
listed above, did not have a significant correlation with the insurance 
claim data for all the seats analyzed. The longitudinal pelvis 
displacement of the BioRID dummy into the seats, an atypical metric in 
whiplash assessments, had the most significant correlation with 
insurance data. NHTSA has also studied intervertebral rotations in low-
speed rear impacts using PMHS and ATD occupants.175 176 177 
NHTSA found the intervertebral rotations of the PMHS subjects to be 
comparable with BioRID rotations \178\ and the PMHS intervertebral 
rotations were found to correlate with PMHS subluxation injuries (an 
incomplete or partial dislocation of a joint or organ).\179\ The use of 
ATD injury metrics in assessing low-speed rear impact injury risk is 
still developing, and further investigation is needed to develop 
metrics or ratings systems with a direct relationship to real world 
whiplash injury. NHTSA's forthcoming research discussed later will 
explore various ATD whiplash criteria.
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    \171\ Aldman, B.: An analytical approach to the impact 
biomechanics of head and neck injury.'' Proceedings of the 39th 
American Association for Automotive Medicine Conference; October 6-
8, 1986, Montreal, QC. 1986.
    \172\ Bostr[ouml]m, Ola, et al. ``A new neck injury criterion 
candidate-based on injury findings in the cervical spinal ganglia 
after experimental neck extension trauma.'' Proceedings of The 1996 
International Ircobi Conference On The Biomechanics Of Impact, 
September 11-13, Dublin, Ireland. 1996.
    \173\ Eichberger, Arno, et al. ``Comparison of different car 
seats regarding head-neck kinematics of volunteers during rear end 
impact.'' Proc. IRCOBI Conf. 1996.
    \174\ Edwards, Marcy A., et al. ``Seat design characteristics 
affecting occupant safety in low-and high-severity rear-impact 
collisions.'' IRCOBI Conference, Florence, Italy, IRC-19-11. 2019.
    \175\ Moorhouse K, Kang Y, Donnelly B, Herriott R, Bolte JH. 
(2012, Nov). Evaluation of The Internal and External Biofidelity of 
Current Rear Impact ATDs to Response Targets Developed from 
Moderate-speed Rear Impacts of PMHS. STAPP Car Crash Journal, 56, 
12S-21.
    \176\ Kang Y, Moorhouse K, Donnelly B, Herriott R, Bolte JH. 
(2012, Nov). Biomechanical Responses of PMHS in Moderate-speed Rear 
Impacts and Development of Response Targets for Evaluating the 
Internal and External Biofidelity of ATDs. STAPP Car Crash Journal, 
56, 12S-20.
    \177\ Kang Y, Moorhouse K, Herriott R, Bolte JH. (2013, May). 
Comparison of Cervical Vertebrae Rotations for PMHS and BioRID II in 
Rear Impacts. Traffic Injury Prevention, 14 (Supplement 1), S136-
S147.
    \178\ Kang Y, Moorhouse K, Icke, K., Stricklin, J., Herriott R, 
Bolte J.H. Rear Impact Head and Cervical Spine Kinematics of BioRID 
II and PMHS in Production Seats (2015, Sept). International Research 
Council on Biomechanics of Injury (IRCOBI), IRC-15-38, 246-260.
    \179\ Kang Y, Moorhouse K, Icke K, Herriott R, Bolte JH. (2014, 
Sept). Head and Cervical Spine Responses of Post Mortem Human 
Subjects in Moderate Speed Rear Impacts. International Research 
Council on Biomechanics of Injury (IRCOBI), Berlin, Germany. IRC-14-
33, 268-285.
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    Multiple studies have shown lack of reproducibility in low-speed 
impacts. In 2007, a study compared the measurements of a BioRID-IIg 
dummy in rear impact sled tests run across 18 identical production 
seats.\180\ The authors were concerned that because the loads in a low-
speed rear impact test are very low, there could be high variability in 
results due to small changes in the test setup. The study ran tests at 
3

[[Page 58030]]

different severities with 6 equivalent repetitions at each severity. 
The authors found that the ATD metrics displayed high variability 
across the equivalent tests. The dummy rebound velocity showed the 
least variability with 2.76%, 1.83% and 1.23% coefficient of variation 
in the low, medium, and high severity tests. The NIC had greater 
variability with a 9.18%, 10.5%, and 13.83% coefficient of variation. 
The neck shear Fx, however, had very high variability with a 21.04%, 
27.86%, and 32.57% coefficient of variation across like tests. After 
computing the ranking score for each of the 6-test series, the authors 
found the scores to vary by 26% from lowest to highest. Because of 
variability in the measurements and ranking scores the authors called 
into question the discriminatory power of the scoring system and noted 
the lack of robustness in the scoring system. This study underlines the 
challenge in developing a low-speed rear impact testing approach with 
high reproducibility. Note that the values of a characteristic for a 
rating system or standard might be set in such a way as to account for 
the variability associated with the test.
---------------------------------------------------------------------------

    \180\ Bortenschlager, Klaus, et al. ``Review of existing injury 
criteria and their tolerance limits for whiplash injuries with 
respect to testing experience and rating systems.'' Proceedings of 
the 20th International Technical Conference on Enhanced safety of 
vehicles, Lyon, France. 2007.
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    The precise understanding of how whiplash injuries occur is 
evolving, but not complete. We seek comment on this approach. Are the 
ATD measurements described above sufficiently objective and correlated 
with whiplash injury? If so, can a low-speed test be conducted in a 
repeatable and reproducible manner that would ensure objective results 
and positive safety outcomes that are equitably distributed across all 
occupant types? Do practicable countermeasures for whiplash injuries 
exist to meet such a regulatory requirement? Would the requirement work 
synergistically with a high-speed dynamic requirement?
(b) High-Speed Test
    A high-speed test would assess rear impact protection at a severity 
where significant rearward deflection of the seat back may occur, and 
occupant retention becomes a concern. This test would assess all four 
of the rear impact protection points. The high inertial forces placed 
on a seat back would test seating system integrity and energy 
absorption capabilities of the seat back through rearward rotation and 
deflection, as well as the ability of the seat belt restraint system to 
maintain retention and support an occupant in rebound. Finally, 
compatibility of the seat and head restraint would be assessed through 
appropriate ATD injury limits. The assessment would likely include neck 
(whiplash or higher-level injury), thorax, spine, and pelvis results, 
but could include other body regions as well.
    Occupant injuries in a high-speed rear impact are primarily severe 
head, neck, and thorax injuries and have clear pathology. Research 
conducted by NHTSA has shown that severe thorax injuries, i.e., rib 
fracture, may also occur in a retained seat occupant through inertia 
and interaction with the seat back in very high-speed rear collisions 
and rigid seat supporting structures.\181\
---------------------------------------------------------------------------

    \181\ Kang, Yun-Seok, et al. ``Biomechanical responses and 
injury assessment of post mortem human subjects in various rear-
facing seating configurations.'' Stapp car crash journal 64 (2020): 
155-212.
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    Seat retention provides continual support to the occupant and is 
important to avoid severe contact injuries and injurious occupant 
kinematics. A lack of occupant retention may also lead to severe 
injuries to passengers other than the forward row occupants through 
occupant-to-occupant interaction. A high-speed test would assess 
seating protection against injury through data from an ATD and related 
seating retention metrics. The occupant retention metrics of concern 
may include the maximum dynamic seat back rotation angle and ATD 
displacement measures. NHTSA seeks comment on the appropriate occupant 
retention metrics and ATD injury criteria at high-speed. We request 
comment on how the availability of specific ATDs might limit or inform 
the selected measurements.
    The forces applied to seat backs in rear impacts range over a 
continuum of severities. The applied inertial forces are proportional 
to the seat base acceleration induced by the crash pulse, the 
occupant's mass, and acceleration. The distribution of occupant mass 
along the seat back influences the torque generated at the seat back 
recliner mechanism, and the torque is proportional to the occupant's 
mass. A high-speed test would need to set a test severity within the 
range of potential real-world severities for which practicable 
countermeasures may be available. Extreme forces on the seat back due a 
rear impact are a relatively rare occurrence in the real-world, with 
the highest forces requiring both a relatively high [Delta]V and 
occupant mass. As noted in our analysis of 2017--2020 CISS data 
reported in Figure II.4, 94% of rear towaway collisions occur at 
[Delta]V of 40 km/h (24.9 mph) or less. Table II.2 indicated that the 
most probable [Delta]V range for MAIS 3+ injuries in rear impacts was 
the 31-40 km/h (19.3-24.9 mph) range. For some seat designs, a dynamic 
test in the [Delta]V range of 35 to 40 km/h (21.7 to 24.9 mph) that is 
conducted with a 50th percentile male ATD would likely lead to 
significant rotation of the seat back and occupant movement along the 
seat back, as described in the 2019 Edwards study.\182\ The authors 
also noted that within the context of a 50th percentile male ATD and 
37.5 km/h (23.3 mph) [Delta]V rear impact sled test, a degree of 
balance was achieved between low and high-speed rear impact protection 
in a range of production seats, as measured by the low-speed ratings 
system, seat back rotation, and occupant displacement in the high-speed 
test. Such a dynamic test conducted with a 95th percentile male ATD or 
at higher [Delta]V, however, would lead to greater forces on the seat 
back with a greater potential for plastic deformation of the seat 
structure, a more extreme test of retention, and potential interaction 
with rear seats. The high-speed test [Delta]V would ideally be high 
enough to be sufficiently representative of real-world crashes to 
generate practicable and, ideally, cost effective countermeasures for 
protection against higher level injuries. NHTSA seeks comment on the 
appropriate test severities for a possible high-speed test and the 
appropriate ATD to utilize.
---------------------------------------------------------------------------

    \182\ Edwards, Marcy A., et al. ``Seat design characteristics 
affecting occupant safety in low-and high-severity rear-impact 
collisions.'' IRCOBI Conference, Florence, Italy, IRC-19-11. 2019.
---------------------------------------------------------------------------

    Positioning of the ATD in the seat may be an important factor in a 
high-speed test. Studies such as the 1994 Strother and James cited 
above, have shown occupant posture to influence injury outcome in rear 
impacts. In addition, the sensitivity of an ATD itself to positioning 
may be a factor to explore. For example, how sensitive are results to 
atypical positions like leaning on the arm rest, creating an off-center 
midsagittal plane for the ATD? NHTSA seeks public comment on the 
appropriate positioning of the ATD in a high-speed rear impact test and 
whether and/or what type of out-of-position testing should be 
performed.
    A well-designed high-speed rear impact test would account for all 
four of NHTSA's rear impact protection points in the context of high 
inertial forces leading to significant rearward deflection of the seat 
back. The performance measures of concern may include retention 
measures such as maximum dynamic seat back rotation angle, but also ATD 
injury metrics relating to thorax and neck injury. In addition to these 
concerns, NHTSA seeks comment regarding what objective rear impact 
protection metrics are of most concern in a high-speed rear impact 
test. Does existing ATD

[[Page 58031]]

technology adequately replicate occupant kinematics at high-speeds? 
What ATD injury metrics would be most objective and relevant?
(c) Rear Impact Delivery Methods
    Another factor to consider for a dynamic testing approach is how 
the crash pulse should be delivered to the seat base. There are two 
basic approaches to consider: a sled (with the seat mounted to either 
the vehicle floor plan or a rigid platform) or moving barrier to 
vehicle approach. This section explores the advantages and 
disadvantages of each approach.
    In experimental study of rear impacts, the most common method for 
crash pulse delivery is a sled-based method. In this approach, a 
moveable sled is accelerated with a high degree of accuracy on a linear 
track. Mounted on the sled may be a rigid platform to which the vehicle 
seat is attached. With appropriate mounting hardware, many types of 
seats can be accommodated without significant modification to the 
setup. However, the mounting of the seat to a rigid platform may not 
transmit loading to the seat identically to how it would be transmitted 
if the seat were mounted to the vehicle floor pan. Thus, a more 
realistic approach would be to mount a floor pan to the sled and mount 
the seat to the floor pan. Such an approach can be expanded to mount 
all or portions of the vehicle body and interior to the sled, 
potentially allowing for multiple ATDs in multiple rows of seats. The 
agency uses a vehicle body mounted sled test approach currently for the 
optional dynamic testing in FMVSS No. 202a.
    Sled-based methods are relatively low cost and deliver a highly 
repeatable pulse that can be readily applied to all seats. This removes 
a degree of uncertainty about test repeatability. However, a sled pulse 
only approximates a real-world crash pulse. A sled offers one-
dimensional translational motion, while actual rear impact crash test 
may contain three-dimensional translational motion and rotation of the 
vehicle, albeit likely relatively small accelerations in the vertical 
and lateral direction. While a sled-based approach is advantageous from 
a cost and repeatability standpoint, it may discount case-specific 
design considerations. In addition, for higher speed impacts, if seats 
were designed around a universal rear impact sled pulse, some seats may 
in turn be over-designed and others under-designed relative to their 
actual need for rear impact protection. This is because the design of 
rear impact protection in seats could consider vehicle factors, e.g., 
vehicle weight and/or stiffness of the vehicle.
    A vehicle approach would deliver a rear impact to a motor vehicle 
using a moving barrier, similar to tests conducted under FMVSS No. 301. 
In fact, while conducting FMVSS No. 301 tests outlined in the 2003 
Saunders study, the agency has added instrumentation to seat backs and 
placed HIII-50M ATDs in the front seats to assess the performance of 
seat backs. As is the case with the vehicle body being mounted to a 
sled, this approach would test rear impact protection in the context of 
the entire vehicle. However, it differs in that the acceleration pulse 
delivered to the seat will be a function of the vehicle's structural 
deformation. In a real collision, the seat base acceleration depends on 
vehicular factors, e.g., vehicle mass and structural characteristics, 
and therefore the moving barrier to vehicle approach would be closer to 
reality compared to a typical sled-based approach. A moving barrier to 
vehicle approach is more of a consideration for higher speed impacts, 
where the vehicle characteristics would have a greater influence on the 
crash pulse. A sled-based approach could tune the sled pulse to the 
actual vehicle crash pulse, if it were known, or use some adjustment to 
the pulse that considers vehicle-based factors. Nonetheless, a barrier 
impact approach would place a greater load on seats of lighter and 
stiffer vehicles because [Delta]V has positive correlation with these 
features if all else is equal.
    The barrier impact approach places the seat in the full vehicle 
environment. However, a sled-based approach allows the possibility of 
the seat mounted on a platform in isolation. Whether a full vehicle or 
isolated seat is tested is less likely to influence testing outcomes in 
low-speed testing. However, high-speed testing will cause much more 
seat back deformation. In certain vehicle environments, such as 
convertibles, two-door cars, standard cab pickup trucks, and vehicles 
with rigid second row seating, there may be structures near the seat 
back which could restrict its rearward movement. Such restrictions 
could be advantageous with respect to meeting seat back rotation 
limits. How such restrictions would influence risk of injury, however, 
is not obvious.
    In summary, a sled-based method using a rigid platform and a 
generic sled pulse is the most cost effective and simplest method for 
inertial loading of a seat. Sled testing using the vehicle floor and 
even more of the actual vehicle would likely increase cost and perhaps 
complexity. The use of generic sled pulses, whether for lower or higher 
speed impact simulation may also potentially allow for greater 
repeatability, while sacrificing closeness to reality. Sled testing 
using a vehicle specific crash pulse would add some complexity and the 
need for knowledge of the crash pulse. A moving barrier to vehicle test 
would be the option but would deliver the best approximation to the 
real-world impact while simplifying crash pulse generation. It would 
have instrumentation measurement complexity similar to sled testing. 
Additionally, a moving barrier to vehicle test may also introduce more 
avenues for test-to-test variability, part of which can be attributed 
to vehicle build variability. NHTSA seeks comment on the different 
approaches for delivering a rear impact crash pulse.
(d) Characteristics and Performance Measures Needed for a Rear Dummy
    As discussed above, fostering the synergistic performance of seats 
suggests dynamic testing should sample at least two different [Delta]V 
regimes: including a low-speed and high-speed test. A different ATD 
could be used for each test to adequately assess the range of occupant 
kinematics that occur as [Delta]V is varied. The primary ATD 
performance measures of concern for a low-speed test relate to whiplash 
injuries and as noted earlier, important characteristics include the 
ability to replicate torso straightening and neck kinematics. These 
factors are also important for biofidelity in a high-speed test along 
with thoracic compression, spine flexibility, and pelvic rotation.\183\
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    \183\ Hagedorn, A., Stammen, J., Ramachandra, R., Rhule, H. et 
al., ``Biofidelity Evaluation of THOR-50M in Rear-Facing Seating 
Configurations Using an Updated Biofidelity Ranking System,'' SAE 
Int. J. Trans. Safety 10(2):291-375, 2022.
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    The HIII-50M has long been widely used for rear impact protection 
research, even though this dummy was developed and validated for 
frontal crash testing. Nonetheless, the HIII-50M has provided an 
effective means of ballasting the seat and measurements of dummy 
kinematics and loading. Over time, significant progress has been made 
on the development of the BioRID ATD, which is designed specifically 
for rear impacts. BioRID performance has thus far been focused on low-
speed testing to assess neck injury risk but has more recently been 
evaluated in higher speed rear impact conditions. Additionally, dynamic 
sled tests are used by ratings groups, academic researchers and 
industrial researchers to assess the performance of seating systems in 
a rear impact, and results are compared with adult volunteers in low-
speed tests and

[[Page 58032]]

PMHS at higher speeds to validate modern ATD 
measurements.184 185 These efforts have built a better 
technological basis for a dynamic test compared to the past.
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    \184\ Willis, Claire, Jolyon Carroll, and Adrian Roberts. ``An 
evaluation of a current rear impact dummy against human response 
corridors in both pure and oblique rear impact.'' Proceedings of the 
19th International Technical Conference of the Enhanced Safety of 
Vehicles, Paper. No. 05-0061. 2005.
    \185\ Croft, Arthur C., and Mathieu MGM Philippens. ``The RID2 
biofidelic rear impact dummy: A pilot study using human subjects in 
low-speed rear impact full scale crash tests.'' Accident Analysis & 
Prevention 39.2 (2007): 340-346.
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    The BioRID 50th percentile male dummy was developed by a Swedish 
team in the 1990s.\186\ The development was in response to low-speed 
rear impact testing using human volunteers indicating that torso 
straightening, and angling of the lower spine were essential for 
accurate cervical spine dynamics,\187\ \188\ and the determination that 
existing ATDs of that era did not properly simulate the cervical 
vertebrae motions. Therefore, development focused on an ATD with more 
realistic spinal motion, particularly in the neck, and one that would 
simulate torso straightening.\189\ The BioRID dummy has an articulated 
mechanical spine and is primarily intended to replicate spinal motion 
in low-speed rear impacts. BioRID vertebrae are connected by linear pin 
joints and a tension cable. This mechanical system shows comparatively 
high torsional, shear, compression, and tension inter-vertebral forces 
in rear impacts.\190\ NHTSA has evaluated the BioRID and believes it is 
the best available 50th percentile male ATD for the low-speed rear 
impact test discussed in this ANPRM, but seeks comment on this topic. 
NHTSA also seeks comment on the potential use of appropriate female 
crash test dummies designed specifically for rear impact to offer a 
more comprehensive assessment of seat performance.
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    \186\ Davidsson, Johan, et al. ``BioRID I: a new biofidelic rear 
impact dummy. '' Proceedings of the International Research Council 
on the Biomechanics of Injury conference. Vol. 26. International 
Research Council on Biomechanics of Injury, 1998.
    \187\ McConnell, Whitman E., et al. Analysis of human test 
subject kinematic responses to low velocity rear end impacts. No. 
930889. SAE Technical Paper, 1993.
    \188\ Ono, Koshiro, and Munekazu Kanno. ``Influences of the 
physical parameters on the risk to neck injuries in low impact speed 
rear-end collisions.'' Accident Analysis & Prevention 28.4 (1996): 
493-499.
    \189\ L[ouml]vsund, Per, and Mats Y. Svensson. ``Suitability of 
the available mechanical neck models in low velocity rear end 
impacts.'' CNR-PFT2 ELASIS International Conference on Active and 
Passive Automobile Safety in Capri, Italy. 1996.
    \190\ Viano, David C., et al. ``Neck biomechanical responses 
with active head restraints: Rear barrier tests with BioRID and sled 
tests with Hybrid III.'' SAE Transactions (2002): 219-237.
---------------------------------------------------------------------------

    For the higher speed rear impact test, NHTSA is examining the use 
of BioRID as well as the HIII-50M and Test device for Human Occupant 
Restraint 50th percentile male (THOR-50M) ATD.\191\ The BioRID has the 
advantages articulated above, but there may be limits to the speed of 
the crash environment that it can be used in and BioRID replicates only 
two-dimensional motion of the spine with injury assessment being 
limited to the cervical spine.
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    \191\ Hagedorn A, Stammen J, Ramachandra R, Rhule H, Thomas C, 
Suntay B, Kang YS, Kwon HJ, Moorhouse K, Bolte IV JH. Biofidelity 
Evaluation of THOR-50M in Rear-Facing Seating Configurations Using 
an Updated Biofidelity Ranking System. SAE Int. J. Trans. Safety 
10(2):2022, https://doi.org/10.4271/09-10-02-0013.
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    The HIII-50M and THOR-50M have limitations due to being designed 
for frontal impacts. Nevertheless, these dummies are typically used in 
studies of high-speed rear impact dynamics and have been used as seat 
occupants in rear impact tests. In the case of high-speed tests these 
ATDs enable the measurement of seat back rotation and retention by 
acting as ballasts that impose a biofidelic inertial load on the seat 
back. The 2019 Edwards study, for example, used the HIII-50M dummy for 
the high-speed test. The HIII-50M is limited because it has a rigid 
thoracic spine so its interaction with a seat back is significantly 
different than a real occupant whose bendable spine conforms with the 
seat cushion profile and structural cross members. The THOR-50M ATD, a 
refinement of the TAD-50M thorax, integrated a new multi-directional 
neck and instrumented pelvis, abdomen, and lower extremity concepts. 
Both the HIII-50M and THOR-50M allow for the measurement of chest 
injury risk. While a high-speed test that uses one of the male ATDs 
discussed above is necessary to assess seating system integrity, a 
comprehensive test of seat retention may also require a test using a 
female ATD. NHTSA seeks comment on the ATDs to use for high-speed rear 
impact tests.
    NHTSA is exploring a low and high severity test as components of a 
unified approach to updating FMVSS No. 207 and the ATD requirements of 
these tests overlap with capabilities of the HIII-50M, THOR-50M, and 
BioRID dummies. NHTSA seeks comment on the benefits and costs, in 
particular the practicability and objectivity concerns, of using 
different ATDs for different rear impact test severities versus the use 
of a single ATD for both low and high-speed testing.

D. Crash Avoidance Technology

    Over the last several years, automatic emergency braking (AEB) and 
forward collision warning (FCW) have become more prevalent in the light 
vehicle fleet. An AEB system uses various sensor technologies and sub-
systems that work together to detect when the vehicle is in a crash 
imminent situation, to automatically apply the vehicle brakes if the 
driver has not done so, or to apply more braking force to supplement 
the driver's braking. A FCW system uses sensors that detect objects in 
front of vehicles and provides an alert to the driver. FCW systems may 
detect impending collisions with any number of roadway obstacles, 
including vehicles. NHTSA has recently published a final rule requiring 
that all new light vehicles be equipped with AEB and FCW systems.\192\ 
NHTSA anticipates that over time, AEB and FCW prevalence in the fleet 
will increase and the technology will improve. Therefore, any future 
rulemaking action related to the upgrade of rear impact protection 
through modification of seat related standards will need to fully 
consider the effects of crash avoidance technology such as AEB and FCW. 
AEB and FCW are expected to reduce the incidence of high-speed rear 
impact collisions, either through avoiding a collision entirely or 
mitigating impact speeds into lower-speed collisions. If AEB and FCW 
have this impact, their availability may in turn affect crash 
frequencies and injury types relevant to this ANPRM, such as the 
incidence of seat back failure in vehicles struck from the rear. AEB 
and FCW may also reduce the incidence of low-speed rear impacts that 
cause injuries such as whiplash in occupants of the struck vehicle. 
However, it is possible that AEB and FCW, by mitigating some high-speed 
impacts into lower-speed collisions, may increase the number of lower-
speed rear impacts. It is not clear what the net impact would be. NHTSA 
seeks comment on how best to consider the effects of this technology on 
the issues discussed in the ANPRM. In particular, how might a change in 
frequency of rear impacts of different velocities impact the benefit-
cost considerations for regulatory changes discussed in this ANPRM, 
such as the seat back strength requirement?
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    \192\ 89 FR 39686 (July 8, 2024). This final rule builds on a 
voluntary commitment, announced by NHTSA in March 2016, by 20 
vehicle manufacturers to make AEB a standard feature on nearly all 
new light vehicles.

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[[Page 58033]]

VII. NHTSA's Forthcoming Research

    NHTSA is pursuing research to build a greater understanding of the 
issues presented in this document. Based upon the current understanding 
of these issues, the goals are to better define the scope of the 
current rear impact safety problem, validate seated ATD measurements in 
rear impacts, quantify rear impact injury risks, attempt to develop 
injury risk curves, and analyze rear impact dynamics and testing 
procedures. Because the understanding of the rear impact problem 
continues to evolve, the priorities and objectives are subject to 
change and likely to evolve as research progresses. Currently, the aim 
is to identify sled test [Delta]Vs, test types (e.g., static versus 
dynamic), test tools (e.g., loading fixture, ATDs) and performance 
limits (e.g., strength requirements, displacement limits, injury 
assessment reference values). It is anticipated that the research 
outcomes will contribute to the determination of whether to propose an 
update to FMVSS No. 202a and FMVSS No. 207 and, if the determination is 
made to do so, provide the basis for such a proposal. The following 
discussion outlines NHTSA's path forward for research activities 
related to this ANPRM.

A. Field Data Analysis and Market Research

    A study of rear impact field data will investigate the scope of the 
rear impact safety problem. NHTSA intends to examine the incidence of 
injuries to the seated front occupant, the types of injuries, the 
degree to which modern occupied seat backs fail or become deformed (by 
row), and which parts of the seat incur yielding (i.e., just the seat 
back, the anchors and seat track, the vehicle floor, etc.). For higher 
speed rear impacts, this is needed to identify the level of crash 
severity that may represent a reasonable dynamic testing level. Overall 
trends will be examined by analyzing aggregate field data and occupant 
injury and multiple seat row interaction. An attempt will be made to 
attribute vehicle occupant injury to seat performance. It is expected 
that manual reviews of case file material will be necessary to discern 
seat performance and failure mechanisms. NHTSA also intends to examine 
how seat designs may have improved across the fleet or how second row 
seats differ in performance from front row seats.

B. Test Procedure Assessment

    NHTSA plans to conduct a sled-based study of rear impact seat back 
and occupant dynamics to develop a greater knowledge base in the 
performance of modern seats in both low and high-speed regimes and to 
investigate the feasibility of a dynamic approach for updating FMVSS 
No. 207 and rear impact protection in general.
1. High-Speed Test
    The agency expects to perform high-speed sled tests across a range 
of [Delta]Vs including the high-speed rear impact fuel integrity test 
performed in FMVSS No. 301 and at speeds identified in the field data 
analysis mention above that result in relatively high risks to vehicle 
occupants. Through this testing, NHTSA will attempt to determine what 
physical characteristics govern occupant protection and what severities 
lead to substantial deformation of seat backs in high-speed rear 
impacts. This testing will take a variety of configurations and serve a 
variety of functions. One important question to be answered is what 
deceleration pulse and/or [Delta]V will achieve the agency's regulatory 
goals, particularly with respect to a front seat occupant intruding 
into the rear seat occupant space. Another important research question 
is whether the deceleration pulse and/or [Delta]V should be vehicle 
specific or generic. It is expected that sled testing will be performed 
with partial vehicles as well as platform mounted seats to decern the 
effect of these two configurations of seat performance as well as to 
assess the challenges related to testing a seat within a vehicle. This 
testing will also help identify the important seat performance 
characteristics and the best way to measure them. We expect to use 
multiple ATDs and PMHS occupants in the seats for a variety of tasks 
discussed below.
2. Exploratory Testing
    NHTSA recently conducted exploratory high-speed rear impact sled 
testing on a series of production seats to gain insight into 
instrumentation and measurement needs for such tests. The test closely 
resembled the 2019 high-speed rear impact tests from the IIHS 
study,\193\ except that NHTSA used the THOR-50M as a normally 
positioned occupant. NHTSA's crash pulse achieved a maximum sled 
acceleration of 15.1 g after approximately 80 ms resulting in a 
[Delta]V of 36 km/h (22.4 mph). The test series consisted of 6 total 
sled tests involving the front driver seat of three different major 
auto manufacturers in 2013 and 2018 MY used passenger vehicles. The 
three models were tested with and without seat belt pretensioners. The 
seats were instrumented with accelerometers, load cells, strain gages 
and camera target standoffs and fixed to the sled buck with an initial 
seat back recline angle of 25[deg]. The time-dependent seat back 
rotation angle was determined by postprocessing film data and 6DX 
(Diversified Technical Systems) sensor package measurements and are 
shown in Figure VII.1 in the case of no pretensioners.
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    \193\ Edwards, Marcy A., et al. ``Seat design characteristics 
affecting occupant safety in low-and high-severity rear impact 
collisions.'' IRCOBI Conference, Florence, Italy, IRC-19-11. 2019.
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    The seat backs reached their maximum rearward rotation at 
approximately twice the point of peak sled acceleration and then, upon 
reversing, decayed to a final recline angle that is greater than the 
initial recline angle. Seat I had the least rearward rotation and its 
final recline angle was the least among the three models. Seat III had 
the most rearward rotation and its final recline angle was the greatest 
among the three models. The difference between the initial and final 
recline angles are a product of irreversible deformation in the seat 
frame and an indication of energy absorbed by the seat. In seat I and 
to a lesser extent seat II, as the rotation angle decayed to the final 
angle there was oscillation of the seat back about the final angle; 
this is a characteristic of spring-mass-damper systems. Seat III had 
significant twisting about the longitudinal axis as seen in the large 
differences between the left and right seat back rotations. A post-test 
visual tear down analysis found that in all seats the side bolsters 
bent inward toward the occupant and deformation was also seen in the 
lower seat frames and pans. This initial series of tests demonstrates 
that rearward excursion and rotation are high-speed seat performance 
metrics that can be reliably obtained in different seat models.
3. Low-Speed Test
    To broadly assess the rear impact protection measures of a seat, 
the performance should be compared in a low- and high-speed test to 
analyze whether improvements in seat performance at high-speed impacts 
sacrifice whiplash injury mitigation at low-speeds. Thus, it is 
expected that seats will be tested in both a low- and a high-speed 
test, to see how the performance compares in both rear impact 
conditions. This study may determine if the design requirements for 
low- and high-speed performance align or contradict one another.
    As stated above, one important factor in test procedure development 
will be exploring the appropriate low- and high-speed deceleration for 
rear impact tests. A reasonable starting point for the lower speed test 
is the head restraint optional dynamic test in FMVSS No. 202a. We are 
aware of other sled pulses used for whiplash assessment by IIHS and 
EuroNCAP, however, and will explore these as well. We will also explore 
the need or acceptability of platform mounted seats versus in-vehicle 
testing. Finally, a key factor for low-speed testing will be the ATD. 
NHTSA expects to focus on the use of the BioRID for these tests.\194\ 
We also expect to assess various whiplash injury criteria.
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    \194\ See discussion at section IV.4., above, for additional 
information related to use of the BioRID.
---------------------------------------------------------------------------

C. Parametric Modeling

    A computational model of seat occupant dynamics in a rear impact 
that is validated against experimental data could provide insight into 
a range of safety issues. It is expected that both ATDs and human body 
models will be used as seat occupants and the impact of various 
occupant characteristics on injury risk can be determined, such as the 
occupant size and gender. NHTSA may also study the extent to which seat 
design specifications have a positive influence on injury risk. A 
computational model can be run over a range of deceleration pulses and 
seat characteristics to determine at which point significant seat 
deformation and the onset of serious injuries to seat occupant occurs.

D. ATD and Injury Risk Function Development

    Rear impact testing with PMHS seat occupants provides biomechanical 
data for ATD evaluation as noted in the NHTSA citations above. By 
comparing equivalent pairs of ATD and PMHS tests, more realistic injury 
risk functions can be developed for the ATD seat occupant in a rear 
impact. NHTSA has, for example, performed extensive work on low-speed 
whiplash injury risk functions for the BioRID. NHTSA expects the BioRID 
to be the focus of low-speed testing in this research; however, various 
whiplash injury criteria will be explored.

[[Page 58036]]

    For high severity research, further PMHS testing will provide the 
injury information to correlate with ATD measurements in an injury risk 
function. This information will also be correlated to seat performance 
parameters to assist in identification of factors that influence injury 
risk. Additionally, both BioRID and THOR-50M will be evaluated for 
high-speed testing. The BioRID has a fully articulated spine but was 
designed specifically for lower speed rear impacts. Thus, durability 
and biofidelity in higher speed rear impacts will need to be evaluated. 
The THOR-50M was not designed for rear impacts, but has thoracic 
measurements not available in BioRID. However, its acceptability for 
overall rear impact injury risk will need further consideration. Once 
injury risk functions are developed, the ATD(s) will be used in a 
broader evaluation of seats on the market against identified 
performance metrics.

E. Cost Analysis

    The purpose of a cost analysis is to determine the financial 
implications of improving rear impact protection. A broad understanding 
will be gained by performing a cost analysis in each aspect of NHTSA's 
research initiative. A tear down analysis of tested seats provides an 
indication of failure mechanisms and protective design measures. The 
cost differential between good and poor performing seats could be 
estimated by quantifying the difference in design measures determined 
through tear down. The computational study could assess the overall 
impact and cost of design changes within a seat; for example, if design 
changes are made to a poorly performing seat for a high-speed test with 
a specific occupant, would these changes in fact have a detrimental 
impact in other scenarios? After the cost differential between good and 
poor performing seats is well defined, then market research and 
assessment of the fleet will determine the overall costs of improving 
rear impact protection.

F. Summary

    NHTSA is pursuing research to gain a greater understanding of the 
modern rear impact protection issue that the agency regulates under 
FMVSS Nos. 207 and 202a. An examination of recent rear impact field 
data is helpful to define the overall safety issue and determine 
whether any countermeasure to a problem is cost effective. This 
document discusses a two-tiered dynamic testing approach. NHTSA is 
pursuing sled testing of rear impacts to explore this dynamic approach 
and has conducted an initial exploratory series of high-speed rear 
impact tests described above. NHTSA has ongoing research in rear impact 
sled testing using PMHS occupants that in turn supports an ATD based 
assessment of rear impact injuries and dynamics. A computational 
parametric study has also been proposed to broadly investigate rear 
impact dynamics and various protection measures. If a rulemaking is 
pursued, NHTSA will also perform research tasks to develop the 
necessary cost and benefit estimates for upgraded rear impact 
protection estimates. NHTSA would like this research to make decisive 
contributions and therefore seeks comment on the research proposed 
here. Would a greater impact be achieved if the agency's resources were 
directed in another area of rear impact protection or more focused in a 
critical area?

VIII. Public Participation

A. How can I inform NHTSA's thinking on this rulemaking?

    Your comments will help us improve this rulemaking. NHTSA invites 
you to provide different views on options NHTSA discusses above, new 
approaches the agency has not considered, new data, descriptions of how 
this ANPRM may affect you, or other relevant information.
    NHTSA welcomes public review of all aspects of this ANPRM, but 
requests comments on specific issues throughout this document. NHTSA 
will consider the comments and information received in developing a 
potential proposal for how to proceed with updating requirements for 
motor vehicles. Your comments will be most effective if you follow the 
suggestions below:
     Explain your views and reasoning as clearly as possible.
     Provide solid technical and cost data to support your 
views.
     If you estimate potential costs, explain how you arrived 
at the estimate.
     Tell NHTSA which parts of the ANPRM you support, as well 
as those with which you disagree.
     Provide specific examples to illustrate your concerns.
     Offer specific alternatives.
     Refer your comments to specific sections of the ANPRM, 
such as the units or page numbers of the preamble.

B. How do I prepare and submit comments?

    Your comments must be in writing. To ensure that your comments are 
filed correctly in the Docket, please include the docket number of this 
document located at the beginning of this notice in your comments.
    Your primary comments should not be more than 15 pages long.\195\ 
You may attach additional documents to your primary comments, such as 
supporting data or research. There is no limit on the length of the 
attachments.
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    \195\ 49 CFR 553.21.
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    Please submit one copy of your comments (two if submitting by mail 
or hand delivery), including the attachments, to the docket via one of 
the methods identified under the ADDRESSES section at the beginning of 
this document. If you are submitting comments electronically as a PDF 
(Adobe) file, we ask that the documents submitted be scanned using an 
Optical Character Recognition (OCR) process, thus allowing NHTSA to 
search and copy certain portions of your submission.
    Please note that pursuant to the Data Quality Act, for substantive 
data to be relied upon and used by the agency, it must meet the 
information quality standards set forth in the OMB and DOT Data Quality 
Act guidelines. Accordingly, NHTSA encourages you to consult the 
guidelines in preparing your comments. DOT's guidelines may be accessed 
at www.transportation.gov/regulations/dot-information-dissemination-quality-guidelines.

C. How can I be sure that my comments were received?

    If you submit comments by hard copy and wish Docket Management to 
notify you upon its receipt of your comments, enclose a self-addressed, 
stamped postcard in the envelope containing your comments. Upon 
receiving your comments, Docket Management will return the postcard by 
mail. If you submit comments electronically, your comments should 
appear automatically in the docket number at the beginning of this 
notice on https://www.regulations.gov. If they do not appear within two 
weeks of posting, we suggest that you call the Docket Management 
Facility at 202-366-9826.

D. How do I submit confidential business information?

    NHTSA is currently treating electronic submission as an acceptable 
method for submitting confidential business information to the agency 
under part 512. If you claim that any of the information or documents 
provided in your response constitutes confidential business information 
within the meaning of 5 U.S.C. 552(b)(4), or are protected from 
disclosure pursuant to 18 U.S.C. 1905, you may either submit your 
request via email or request a secure file transfer

[[Page 58037]]

link from the Office of the Chief Counsel contact listed below. You 
must submit supporting information together with the materials that are 
the subject of the confidentiality request, in accordance with part 
512, to the Office of the Chief Counsel. Do not send a hardcopy of a 
request for confidential treatment to NHTSA's headquarters.
    Your request must include a request letter that contains supporting 
information, pursuant to Sec.  512.8. Your request must also include a 
certificate, pursuant to Sec.  512.4(b) and part 512, appendix A.
    You are required to submit one unredacted ``confidential version'' 
of the information for which you are seeking confidential treatment. 
Pursuant to Sec.  512.6, the words ``ENTIRE PAGE CONFIDENTIAL BUSINESS 
INFORMATION'' or ``CONFIDENTIAL BUSINESS INFORMATION CONTAINED WITHIN 
BRACKETS'' (as applicable) must appear at the top of each page 
containing information claimed to be confidential. In the latter 
situation, where not all information on the page is claimed to be 
confidential, identify each item of information for which 
confidentiality is requested within brackets: ``[ ].''
    You are also required to submit one redacted ``public version'' of 
the information for which you are seeking confidential treatment. 
Pursuant to Sec.  512.5(a)(2), the redacted ``public version'' should 
include redactions of any information for which you are seeking 
confidential treatment (i.e., the only information that should be 
unredacted is information for which you are not seeking confidential 
treatment). For questions about a request for confidential treatment, 
please contact Dan Rabinovitz in the Office of the Chief Counsel at 
[email protected].

E. Will the agency consider late comments?

    NHTSA will consider all comments received to the docket before the 
close of business on the comment closing date indicated above under the 
DATES section. NHTSA will consider any late-filed comments to the 
extent possible.

F. How can I read the comments submitted by other people?

    You may read the comments received by Docket Management in hard 
copy at the address given above under the ADDRESSES section. The hours 
of the Docket Management office are indicated above in the same 
location. You may also read the comments on the internet by doing the 
following:
    (1) Go to https://www.regulations.gov.
    (2) Regulations.gov provides two basic methods of searching to 
retrieve dockets and docket materials that are available in the system:
    a. The search box on the home page which conducts a simple full-
text search of the website, into which you can type the docket number 
of this notice and
    b. ``Advanced Search,'' which is linked on the regulations.gov home 
page, and which displays various indexed fields such as the docket 
name, docket identification number, phase of the action, initiating 
office, date of issuance, document title, document identification 
number, type of document, Federal Register reference, CFR citation, 
etc. Each data field in the advanced search function may be searched 
independently or in combination with other fields, as desired. Each 
search yields a simultaneous display of all available information found 
in regulations.gov that is relevant to the requested subject or topic.
    (3) Once you locate the docket at httsp://www.regulations.gov, you 
can download the comments you wish to read. We note that because 
comments are often imaged documents rather than word processing 
documents (e.g., PDF rather than Microsoft Word), some comments may not 
be word searchable.
    Please note that, even after the comment closing date, NHTSA will 
continue to file relevant information in the Docket as it becomes 
available. Further, some people may submit late comments. Accordingly, 
NHTSA recommends that you periodically check the Docket for new 
material.

IX. Regulatory Analyses and Notices

A. Executive Order (E.O.) 12866, E.O. 13563, and E.O. 14094 and DOT 
Regulatory Policies and Procedures

    The agency has considered the impact of this rulemaking action 
under Executive Order (E.O.) 12866, E.O. 13563, E.O. 14094, and the 
Department of Transportation's regulatory procedures DOT Order 2100.6A. 
This ANPRM was determined to be significant under E.O. 12866 and was 
reviewed by the Office of Management and Budget.
    This ANPRM presents possible avenues for updating regulations 
regarding occupant protection in rear impact and seeks public comment 
to develop information that may inform a future proposal. NHTSA is 
using this ANPRM to solicit public feedback before potentially 
proceeding with a proposed rule.
    We have asked commenters to answer a variety of questions to elicit 
practical information about alternative approaches and relevant 
technical data, which will enable analysis of the costs and benefits of 
a possible future proposal.

B. Paperwork Reduction Act

    Under the Paperwork Reduction Act of 1995 (PRA), a person is not 
required to respond to a collection of information by a Federal agency 
unless the collection displays a valid OMB control number. This ANPRM 
would not establish any new information collection requirements.

C. Privacy Act

    DOT solicits comments from the public to better inform its 
rulemaking process. DOT posts these comments, without edit, including 
any personal information the commenter provides, to 
www.regulations.gov, as described in the system of records notice (DOT/
ALL-14 FDMS), which can be reviewed at www.dot.gov/privacy. Please note 
that anyone is able to search the electronic form of all comments 
received into any of our dockets by the name of the individual 
submitting the comment (or signing the comment, if submitted on behalf 
of an association, business, labor union, etc.). For information on 
DOT's compliance with the Privacy Act, please visit https://www.transportation.gov/privacy.

D. Plain Language

    Executive Order 12866 requires each agency to write all rules in 
plain language. Application of the principles of plain language 
includes consideration of the following questions:
     Have we organized the material to suit the public's needs?
     Are the requirements in the document clearly stated?
     Does the document contain technical language or jargon 
that isn't clear?
     Would a different format (grouping and order of sections, 
use of headings, paragraphing) make the document easier to understand?
     Would more (but shorter) sections be better?
     Could we improve clarity by adding tables, lists, or 
diagrams?
     What else could we do to make the document easier to 
understand?
    If you have any responses to these questions, please include them 
in your comments.

E. Regulation Identifier Number (RIN)

    The Department of Transportation assigns a regulation identifier 
number (RIN) to each regulatory action listed in the Unified Agenda of 
Federal

[[Page 58038]]

Regulations. The Regulatory Information Service Center publishes the 
Unified Agenda in April and October of each year. You may use the RIN 
contained in the heading at the beginning of this document to find this 
action in the Unified Agenda.

X. Conclusion

    In accordance with 49 CFR part 552, NHTSA grants in part and denies 
in part the petitions by Mr. Saczalski and Mr. Cantor and denies the 
CAS petition.

    Issued in Washington DC, under authority delegated in 49 CFR 
1.95, 501.5, and 501.8.
Jack Danielson,
Executive Director.
[FR Doc. 2024-15390 Filed 7-15-24; 8:45 am]
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