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Proposed Rule2024-15390

Federal Motor Vehicle Safety Standards; Seating Systems

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Published

July 16, 2024

Issuing agencies

Transportation DepartmentNational Highway Traffic Safety Administration

Abstract

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.

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[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 [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[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:
<bullet> Federal eRulemaking Portal: Go to <a href="https://www.regulations.gov">https://www.regulations.gov</a>. Follow the online instructions for submitting
comments.
<bullet> Mail: Docket Management Facility, U.S. Department of
Transportation, 1200 New Jersey Avenue SE, Room W12-140, Washington, DC
20590-0001.
<bullet> 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 <a href="https://www.regulations.gov">https://www.regulations.gov</a>, 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
<a href="/cdn-cgi/l/email-protection#7337121d1a161f5d2112111a1d1c051a070933171c075d141c05">[email&#160;protected]</a> or (202) 366-8534.

FOR FURTHER INFORMATION CONTACT: Mr. Tyler Brosten, Office of
Crashworthiness Standards (Telephone: 202-366-1740; Email:
<a href="/cdn-cgi/l/email-protection#186c61747d6a367a6a776b6c7d76587c776c367f776e">[email&#160;protected]</a>, Facsimile: 202-493-2739), or Mr. Eli Wachtel,
Office of Chief Counsel (Telephone: 202-366-2992; Email:
<a href="/cdn-cgi/l/email-protection#afcac3c681d8ceccc7dbcac3efcbc0db81c8c0d9">[email&#160;protected]</a>). 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 <a href="https://www.regulations.gov/">https://www.regulations.gov/</a>.
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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 <a href="https://www.regulations.gov/">https://www.regulations.gov/</a>.
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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. <a href="http://www.aaam.org">www.aaam.org</a>.
\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
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Crash type by initial point of impact Fatal Injury Property damage only Total
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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
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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
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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
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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.
---------------------------------------------------------------------------

\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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

\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\ <a href="https://www.nhtsa.gov/research-data/research-testing-databases#/vehicle/">https://www.nhtsa.gov/research-data/research-testing-databases#/vehicle/</a>.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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).
---------------------------------------------------------------------------

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.
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\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, <a href="https://www.autonews.com/suppliers/high-tech-headrest-designed-reduce-whiplash-injuries">https://www.autonews.com/suppliers/high-tech-headrest-designed-reduce-whiplash-injuries</a>.
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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.
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\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 <a href="http://Regulations.gov">Regulations.gov</a>, 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).
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\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.
---------------------------------------------------------------------------

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).
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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\
---------------------------------------------------------------------------

\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.
---------------------------------------------------------------------------

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.
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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.
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\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 (<a href="http://unece.org">unece.org</a>).
\139\ UNECE Regulation No. 44, Uniform provisions concerning the
approval of restraining devices for child occupants of power-driven
vehicles (``Child Restraint System'').
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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 <a href="http://Regulations.gov">Regulations.gov</a>, 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.

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 <a href="http://Regulations.gov">Regulations.gov</a>, 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
<a href="http://Regulations.gov">Regulations.gov</a>, 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: <a href="https://www.iseecars.com/most-convertibles-by-state-2017-study">https://www.iseecars.com/most-convertibles-by-state-2017-study</a>.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

\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.
---------------------------------------------------------------------------

(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/<a href="https://www.nhtsa.gov/sites/nhtsa.gov/files/documents/tread.pdf">https://www.nhtsa.gov/sites/nhtsa.gov/files/documents/tread.pdf</a>.
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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.
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\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 ave

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