# Federal Motor Vehicle Safety Standards; Seating Systems

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3A2024-15390

## Record

- **Collection:** Federal Register
- **Document type:** Proposed Rule
- **Published:** July 16, 2024
- **Citation:** 89 FR 57998

## Text

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.

SUMMARY:

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

DATES:

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

ADDRESSES:

You may submit written comments, identified by docket number or RIN, by any of the following methods:

•
Federal eRulemaking Portal:
Go to
https://www.regulations.gov.
Follow the online instructions for submitting comments.

•
Mail:
Docket Management Facility, U.S. Department of Transportation, 1200 New Jersey Avenue SE, Room W12-140, Washington, DC 20590-0001.

•
Hand Delivery or Courier:
1200 New Jersey Avenue SE, West Building, Ground Floor, Room W12-140, Washington, DC, between 9 a.m. and 5 p.m. E.T., Monday through Friday, except Federal holidays. To be sure someone is there to help you, please call 202-366-9826 before coming.

Instructions:
For detailed instructions on submitting comments and additional information on the rulemaking process, see the Public Participation heading of the
SUPPLEMENTARY INFORMATION
section of this document. Note that all comments received will be posted without change to
https://www.regulations.gov,
including any personal information provided. Please see the “Privacy Act” discussion in Section IX. Regulatory Analyses and Notices.

Confidential Business Information:
If you claim that any of the information or documents provided to the agency constitute confidential business information within the meaning of 5 U.S.C. 552(b)(4), or are protected from disclosure pursuant to 18 U.S.C. 1905, you must submit supporting information together with the materials that are the subject of the confidentiality request, in accordance with part 512, by email or secure file transfer to the Office of the Chief Counsel, Litigation and Enforcement Division. Do not send a hardcopy of a request for confidential treatment to NHTSA's headquarters.

Your request must include a request letter that contains supporting information, pursuant to § 512.8. Your request must also include a certificate, pursuant to § 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 § 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 § 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
Daniel.Rabinovitz@dot.gov
or (202) 366-8534.

FOR FURTHER INFORMATION CONTACT:

Mr. Tyler Brosten, Office of Crashworthiness Standards (Telephone: 202-366-1740; Email:
tyler.brosten@dot.gov,
Facsimile: 202-493-2739), or Mr. Eli Wachtel, Office of Chief Counsel (Telephone: 202-366-2992; Email:
eli.wachtel@dot.gov
). 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

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.

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.

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.

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.

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.

8
The head restraint and seat back are interconnected parts of the seating system.

9
49 CFR 571.202(a) S4.2.7.

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

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.

10
These petitions, dated October 28, 2014 (Environmental Research and Safety Technologists, Inc.), and September 28, 2015 (ARCCA), are available in the rulemaking docket at
https://www.regulations.gov/.

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.

11
This petition, dated March 9, 2016, is also available in the rulemaking docket at
https://www.regulations.gov/.

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.

12
The severity of injury is ranked in accordance with the Abbreviated Injury Scale (AIS). An AIS level 3 injury is a serious injury, level 4 a severe injury, and levels 5 and 6 are critical and fatal injuries, respectively.
www.aaam.org.

13
Prasad, Priya, et al. “Relationships between passenger car seat back strength and occupant injury severity in rear end collisions: Field and laboratory studies.”
SAE transactions
(1997): 3935-3967.

14
Parenteau, Chantal S., and David C. Viano. “Serious head, neck and spine injuries in rear impacts: frequency and sources.”
IRC-21-10, IRCOBI Conference.
2021.

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.

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.

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

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.

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.

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.

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

Crash type by initial point of impact
Crash severity
Fatal
Number
Percent
Injury
Number
Percent
Property damage only
Number
Percent
Total
Number
Percent

Single-Vehicle Crashes:

Front
10,883
67.9
358,800
77.1
791,913
73.1
1,161,597
74.2

Left Side
890
5.6
21,960
4.7
54,317
5.0
77,167
4.9

Right Side
886
5.5
33,795
7.3
85,283
7.9
119,965
7.7

Rear
222
1.4
16,334
3.5
84,915
7.8
101,473
6.5

Noncollision
1,714
10.7
27,237
5.9
40,898
3.8
69,849
4.5

Other/Unknown
1,430
8.9
7,157
1.5
25,991
2.4
34,580
2.2

Total
16,025
100.0
465,285
100.0
1,083,319
100.0
1,564,629
100.0

Multiple-Vehicle Crashes:

Front
15,987
62.9
1,183,348
54.3
2,354,919
49.3
3,554,254
50.9

Left Side
3,221
12.7
224,185
10.3
522,635
10.9
750,041
10.7

Right Side
2,649
10.4
206,256
9.5
486,970
10.2
695,875
10.0

Rear
2,772
10.9
561,310
25.8
1,395,634
29.2
1,959,717
28.1

Noncollision
76
0.3
702
0.0
2,474
0.1
3,253
0.0

Other/Unknown
704
2.8
2,787
0.1
17,515
0.4
21,007
0.3

Total
25,409
100.0
2,178,589
100.0
4,780,149
100.0
6,984,146
100.0

All Crashes:

Front
26,870
64.9
1,542,149
58.3
3,146,832
53.7
4,715,850
55.2

Left Side
4,111
9.9
246,145
9.3
576,953
9.8
827,209
9.7

Right Side
3,535
8.5
240,051
9.1
572,254
9.8
815,839
9.5

Rear
2,994
7.2
577,646
21.8
1,480,551
25.3
2,061,189
24.1

Noncollision
1,790
4.3
27,939
1.1
43,372
0.7
73,101
0.9

Other/Unknown
2,134
5.2
9,945
0.4
43,507
0.7
55,586
0.7

Total
41,434
100.0
2,643,874
100.0
5,863,467
100.0
8,548,775
100.0

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 ΔV
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
ΔV 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 ΔV (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

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 ΔV for large trucks would be on average smaller than for light vehicles.
23

23
ΔV 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

Injury severity/initial point of impact
Vehicle type

Passenger
cars

Light
trucks

Large
trucks

Buses

Other/
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 (ΔV). 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.

EP16JY24.006

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.

EP16JY24.007

EP16JY24.008

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)) ΔV range. Table II.3 provides tabulated annual occupant injuries in rear collisions according to injury severity and ΔV. For occupants in a known ΔV rear impact crash, the majority of injuries are estimated to be no injury (MAIS 0) in all ΔV ranges. The most probable known ΔV 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 ΔV in towed rear crashes. The highest risk for MAIS 2 injuries is 8.4% (= 891/10,630) for 51+ km/h (31.7+ mph) ΔV 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) ΔV 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%.

EP16JY24.009

Table II.4—Annual Rear Impact Injury by ΔV
[2017-2020 CISS]

ΔV
(km/h)

MAIS
0

Whiplash

MAIS 1 no
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 ΔV
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

EP16JY24.010

EP16JY24.011

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

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) ΔV 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 ΔV less than 20 km/h (12.4 mph). For only towaway rear impacts (not shown graphically) this ΔV 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 ΔV segmentation.

Table II.5—Adjustments to Whiplash Injuries To Account for Non-Towed Crashes

ΔV
(km/h)

Ratio total
to towed
(82-86 NASS)

Towed whiplash
injury
(2017-2020 CISS)

Compensated
whiplash
injury

Unknown ΔV
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 ΔV

18,570
96,819

Total

31,207
161,372
161,372

EP16JY24.012

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 ΔVs of 21 km/h (13 mph) or less, 86% occur at ΔVs less than 32 km/h (20 mph) and 94% occur at ΔVs 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 ΔV 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 ΔV 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

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.

EP16JY24.013

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.

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

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

7. 1989—NHTSA Receives Petitions for Rulemaking on Revisions to FMVSS No. 207

In 1989, Kenneth J. Saczalski and Alan Cantor submitted their first petitions for rulemaking on this subject to NHTSA.
55 56

Saczalski sought an increase in the seat back moment requirement in FMVSS No. 207 from 373 Nm (3,300 in-lb) to 6,330 Nm (56,000 in-lb),a factor of 17 increase. The aim was to reduce the incidence of injuries due to ramping and ejection in rear-end crashes. On July 24, 1989, NHTSA notified Saczalski that his petition was granted.

55
Docket 89-20-No.1-001 or Docket NHTSA-1996-1817-0002. Both petitions have significant overlap to the 2014 Saczalski and 2015 Cantor petitions discussed in this document.

56
The previous NHTSA Seat Dockets, 89-20 Notices 1-3, are now available on the Docket Management System (DMS) at NHTSA-1998-1817, -4047 and -4064, respectively.

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

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

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

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 ΔV (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

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 ΔV 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

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.

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 ΔVs 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 ΔV of 16, 24, and 40 km/h (9.9, 14.9, and 24.9 mph). After assessing the range of sampled speeds and ATD measurements, Prasad hypothesized that (all else being equal) stiffening of the baseline 1996 production seats can result in an overall increase in whiplash type injuries at low-to-moderate speeds and a greater potential for serious neck injury at higher speeds, in addition to other conclusions. This study, however, has limitations. Many of the pickups in the crash data analyzed may not have had head restraints because trucks were not required to have head restraints until MY 1993. Moreover, a rotationally rigid seat represents the extreme end of the debate around the seat strength set by FMVSS No. 207. While modern production seats are characterized by a seat strength many times the value set by FMVSS No. 207, these seats also display a degree of balance between high and low-speed rear impact protection and the characteristic of rearward rotation of the seat back.

Other research suggests that optimizing seat back design, including stiffness, can reduce injury risks in rear impact. In a 1996 study, Svensson, et al.
101

analyzed the influence of seat back properties on neck injury using the HIII ATD with a Rear Impact Dummy (RID)-neck in low-speed rear collision sled testing. The study found that it was possible to significantly reduce harmful head-neck motion of the ATD by optimizing the head-to-head restraint gap, seat back frame stiffness, and characteristics of the seat-back cushion.

101
Svensson, Mats Y., et al. “The influence of seat-back and head-restraint properties on the head-neck motion during rear-impact.”
Accident Analysis & Prevention
28.2 (1996): 221-227.

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.

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.

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

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

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.

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

105
Wiklund, Kristina; Larsson, Håkan (1 February 1998). “Saab Active Head Restraint (SAHR)—Seat Design to Reduce the Risk of Neck Injuries in Rear Impacts.” Journal of Passenger Cars.

106
“Can a high-tech headrest reduce whiplash injuries,” Automotive News, August 14, 2022,
https://www.autonews.com/suppliers/high-tech-headrest-designed-reduce-whiplash-injuries.

In the early 1990s, General Motors (GM) Research and Development Center undertook an in-depth study of seat characteristics to improve occupant safety in rear impacts. In general, the GM seat design fostered movement of the pelvis rearward and into the lower portion of the seat back frame in a way that would preclude ramping and reduce the moment arm on the seat back. A key design component was to balance the stiffness of the seat resisting the rearward movement of the pelvis against the ability of the seat back frame to resist backward rotation. GM established their own quasi-static test for the purposes of assuring that a given seat met the design parameters. It was a destructive test that made use of a 50th percentile male dummy loaded rearward into the seat back through the lumbar joint. The dummy was free to move up, down, and sideways during rear loading. The test also allowed the seat back to rotate rearward and twist in a manner similar to what was observed in sled testing. Eventually, GM's seat design targets were published by SAE International.
107

The targets were derived from various measurements taken during their quasi-static test. The targets contained many more parameters than FMVSS No. 207's single requirement to withstand a 373 Nm (3,300 in-lb) moment (see table 1 for a list of the parameters). Notably, the GM parameters included a criterion that limited the seat stiffness to no more than 25 kN/m, while attempting to assure that the seat had sufficient energy absorbing properties. GM stressed that simply raising the FMVSS No. 207 moment beyond 373 Nm would not achieve a desirable seat design. According to GM, increasing only the seat back's stiffness would reduce the beneficial effects of yielding.

107
Viano, David C. “Role of the seat in rear crash safety.”
Warrendale, PA: Society of Automotive Engineers, 2002. 514
(2002).

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.

108
About one third of the seats tested by the agency in 1998 were dual recliners. This was a convenience sample not intended to be representative of the fleet. Molino L (1998), Determination of Moment-Deflection Characteristics of Automobile Seat Backs, NHTSA, November 25, 1998.
See

Regulations.gov
, Docket document no. NHTSA-1998-4064-0026.

109
Viano, David C., et al. “Occupant responses in conventional and ABTS seats in high-speed rear sled tests.”
Traffic injury prevention
19.1 (2018): 54-59.

110
Herbst, B.R., Meyer, SE, Oliver, A.A., and Forrest, S.M. Rear impact test methodologies: quasistatic and dynamic. Proceedings of 21st International Technical Conference on the Enhanced Safety of Vehicles, 2009. Stuttgart, Germany.

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 ΔV 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° to 47° 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 ΔV 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 ΔV of 16 km/h (10 mph).

111
Edwards, Marcy A., et al. “Seat design characteristics affecting occupant safety in low-and high-severity rear-impact collisions.”
IRCOBI Conference, Florence, Italy, IRC-19-11.
2019.

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

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.

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.

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 ΔV 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.”

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.

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.

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.

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 ΔV 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 ΔV test is very severe for a rear impact. The CISS data reported in section II.B indicates this speed represents more than 95% of all towaway rear impacts. The authors found that rib fractures occurred in the PMHSs due to a complex combination of chest compression and expansion with upward shear loading. The majority of rib fractures occurred after peak chest compression when the abdominal contents shifted rearward and upward into the thorax due to the ramping motion of the PMHS, which created a combined loading (compression/tension and shear) to the thorax. Similar magnitudes of rib strains were observed regardless of seat types, while strain modes varied according to recline angle and seat type. Fewer injuries were seen with a more upright 25-degree seat back, compared to a more typical initial seat angle of 45-degree seat back.

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

D. Summary

While progress has been made in understanding rear impact injuries, the literature continues to point toward the need for a greater understanding before conclusions can be drawn about the exact mechanisms of injury and the risk factors involved, particularly in regards to whiplash.
127

Likewise, important safety improvements have been made in production seats over the last 50 years and a greater understanding of the relationship between seat back characteristics and injury has been achieved, but questions remain with respect to precisely quantifying protective characteristics. The continued uncertainty around how best to protect occupants as well as the varied approaches and developments in rear impact technology suggests that, as NHTSA considers amendments to FMVSS Nos. 207 and 202a, there is value in preserving industry flexibility in seat back and head restraint design and strength parameters to allow further

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.

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

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

135
Jermakian JS, Arbogast KB, Durban DR, Kallan NJ (2008), Injury risk for children in rear impacts: role of the front seat occupant, 52nd AAAM Annual Conference, Annals of Advances in Automotive Medicine, October 2008.

136
The 12-month-old dummy, known as the (CRABI) dummy, is already integrated into subpart P of part 572.

137
Injury reference values recommended by NHTSA for the CRABI and HIII-95M, when used to assess air bags, are contained within: Eppinger R, Sun E, Kuppa S, Saul R (2000), Supplement: development of improved injury criteria for the assessment of advanced automotive restraint systems-II, National Highway Traffic Safety Administration, March 2000.

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

3. FMVSS No. 213, Child Restraint Seats

Saczalski asked NHTSA to include a rear impact requirement for child restraint systems within FMVSS No. 213, which does not contain such requirements. He suggested using the same test and performance criteria as the European standard for child restraint systems, United Nations Economic Commission for Europe Regulation 44 (ECE R.44),
138

but run at a higher test speed of 40 km/h.
139

The ECE standard contains requirements for various sized child dummies subjected to a 30 km/h rear impact. Like FMVSS No. 213, the European standard also includes requirements for a frontal impact, but those are not discussed in Saczalski's petition.

138
Uniform Provisions Concerning the Approval of Restraining Devices for Child Occupants of Power-Driver Vehicles, (Child Restraint Systems), ECE R.44, E/ECE/324/Rev (
unece.org
).

139
UNECE Regulation No. 44, Uniform provisions concerning the approval of restraining devices for child occupants of power-driven vehicles (“Child Restraint System”).

C. Petition of Alan Cantor

In a letter dated September 28, 2015, Alan Cantor of ARCCA petitioned NHTSA to revise FMVSS No. 207 by implementing new requirements for seat back strength involving a crash test with an ATD. He also requested that NHTSA reinstate a provision to FMVSS No. 209, “Seat belt assemblies,” that he states would prevent occupant injuries in rear impacts.

1. Use of FMVSS No. 301, “Fuel System Integrity,” To Upgrade FMVSS No. 207

Cantor requested a dynamic test to assess seat back loading by occupants of different sizes. He envisioned the use of the current FMVSS No. 301 procedure with Hybrid III 50th Percentile male dummies (HIII-50M). Additionally, Cantor requested that a test be performed at oblique impact angles to assess the potential of excessive seat back twisting that Cantor stated could facilitate rearward ramping and an out-of-position orientation of the occupant in the seat during subsequent impacts. A full vehicle test was also envisioned, but alternatively Cantor suggested that a sled test could be run using an impulse equivalent to that produced by the dynamic procedure. Cantor did not request a change to the static requirements of FMVSS No. 207, nor did he call for the use of rear seated child dummies in the dynamic, full vehicle test. Under Cantor's rationale, the test with the HIII-50M dummies would serve as the basis for a new set of FMVSS requirements. The requirements would apply to front seats as well as rear “bucket” seats, such as those within minivans, that he suggests may also have a propensity to collapse.

2. Rearward Rotation Limit and Structural Symmetry Requirement

Cantor recommended a pass/fail limit for rearward seat back rotation of no more than 15 degrees from its initial seat back orientation (measured in real-time during the test). For the oblique impacts, there would be a requirement that the differential rearward deflection of the seat back is no more than 10 degrees between the left and right sides. According to Cantor, this will assure structural symmetry of the seat to prevent excess twisting of the seat under load, which can lead to ramping or out-of-position orientation of an occupant if subsequent impacts occur.

3. Additional Dynamic Testing and NCAP Implementation

Cantor also requested another dynamic test to assess seat back loading to be performed with a Hybrid III 95th male dummy (HIII-95M) and to incorporate results into the NCAP star rating for the vehicle. This test would be performed in a manner similar to the current FMVSS No. 301 procedure, but at an impact speed of the barrier that is 8 km/h (5 mph) faster than the current FMVSS No. 301 speed. He argues that it would serve to inform consumers on whether a given vehicle seat back has the propensity to collapse. Cantor states it would also provide incentive to manufacturers to develop enhancements to rear impact crash protection.

Cantor recommended the same pass/fail limit for rearward seat back rotation for the NCAP tests as he recommended for the FMVSS No. 301 impacts. Cantor did not specify how the results would be factored into the NCAP rating.

4. FMVSS No. 209, Seat Belt Assemblies

Cantor requested that NHTSA restore S4.1(b), which NHTSA deleted in a final rule published in 1999.
140

This provision required the lap belt portion of the seat belt be designed to remain on the pelvis under all crash conditions. Cantor states that restoring S4.1(b) would assure that vehicles will be equipped with seat belt technologies that prevent ramping in rear impact crashes.

140
64 FR 27203 (May 19, 1999).

D. NHTSA's Analysis of Saczalski and Cantor Petitions

NHTSA is denying in part the Saczalski and Cantor petitions as they pertain to the following recommendations: Cantor's requested amendments to NCAP and request to restore anti-ramping language to FMVSS No. 209, and Saczalski's requests to add a rear impact test to FMVSS No. 213 and a cargo test requirement to FMVSS No. 207. As part of this rulemaking effort to update FMVSS No. 207 and to facilitate informed comment, NHTSA is granting the petitions in part with regard to updating the strength requirement in FMVSS No. 207, the structural symmetry requirement requested by Cantor, and the possible development of new test procedures for seat back strength under FMVSS No. 207. NHTSA notes that, at this time, insufficient information has been provided to support the petitioners' suggested specific strength levels or test designs, but NHTSA seeks comment on this issue. The remainder of this section provides NHTSA's opinions on the recommendations in the petitions to provide context and information to support informed comment on an update to FMVSS No. 207. Later in this document, we discuss NHTSA's current thinking on an integrated and unified approach to rear impact protection and seeks comment on that approach.

1. Analysis of Data and Research Provided by Cantor and Saczalski Regarding Safety Need

In the past, NHTSA and petitioners on this topic have not been able to demonstrate that a safety need exists regarding the seat back strength requirement in FMVSS No. 207.
141

In their petitions, Saczalski and Cantor both implied that factors related to child safety have given rise to a new safety need for stronger seat backs. NHTSA acknowledges that there is evidence that, in some crash scenarios, seat back deformation or rearward movement due to component failure can lead to injury, but NHTSA believes that the petitioners have not provided sufficient supporting data to demonstrate a worsening safety need related to seat back strength compared to NHTSA's past determination. NHTSA discusses the materials provided by petitioners below and seeks comment on this question.

141

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

In support of his petition, Saczalski references the CHoP study. NHTSA agrees with Saczalski that the 2008 CHoP study is useful for understanding the levels of risk to which children in rear seats are exposed, but the CHoP study did not determine that this risk was associated with front seat back strength. The i

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2024-15390. Public record. Not legal advice.