Federal Motor Vehicle Safety Standards; Occupant Crash Protection, Seat Belt Reminder Systems, Controls and Displays

Federal RegisterJan 3, 2025

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. NHTSA-2024-0071]

RIN 2127-AL37

Federal Motor Vehicle Safety Standards; Occupant Crash Protection, Seat Belt Reminder Systems, Controls and Displays

AGENCY:

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

ACTION:

Final rule.

SUMMARY:

This document amends Federal Motor Vehicle Safety Standard (FMVSS) No. 208, “Occupant crash protection,” to require a seat belt use warning system for rear seats. The rule also updates and enhances the current seat belt warning requirements for the driver's seat belt and extends these requirements to the front outboard passenger seat. The final rule applies (with some exceptions) to passenger cars, trucks, most buses, and multipurpose passenger vehicles with a gross vehicle weight rating of 4,536 kilograms (10,000 pounds) or less. This document also makes related amendments to FMVSS No. 101, “Controls and displays.”

DATES:

Effective date:

The effective date of this final rule is March 4, 2025.

Compliance date:

The compliance date of this final rule is September 1, 2026, for the front seat belt warning system requirements and September 1, 2027, for the rear seat belt warning system requirements, with optional early compliance permitted. Multi-stage manufacturers and alterers would have an additional year to comply.

Petitions for reconsideration:

Petitions for reconsideration of this final rule must be received not later than February 18, 2025.

ADDRESSES:

Petitions for reconsideration of this final rule must refer to the docket and notice number set forth above and be submitted to the Administrator, National Highway Traffic Safety Administration, 1200 New Jersey Avenue SE, Washington, DC 20590. Note that all petitions received will be posted without change to

www.regulations.gov,

including any personal information provided.

Privacy Act:

Petitions will be placed in the docket. Anyone is able to search the electronic form of all documents received into any of our dockets by the name of the individual submitting the comment (or signing the comment, if submitted on behalf of an association, business, labor union, etc.). You may review DOT's complete Privacy Act Statement in the

Federal Register

published on April 11, 2000 (Volume 65, Number 70; Pages 19477-78) or you may visit

https://www.transportation.gov/individuals/privacy/privacy-act-system-records-notices.

FOR FURTHER INFORMATION CONTACT:

For non-legal issues, you may contact Ms. Carla Rush, Office of Crashworthiness Standards, Telephone: (202) 366-4583; Email:

carla.rush@dot.gov;

Facsimile: (202) 493-2739. For legal issues, you may contact Mr. John Piazza (

John.Piazza@dot.gov

) or Eli Wachtel (

Eli.Wachtel@dot.gov

), Office of Chief Counsel, Telephone: (202) 366-2992; Facsimile: (202) 366-3820. The address of these officials is: the National Highway Traffic Safety Administration, 1200 New Jersey Avenue SE, Washington, DC, 20590.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Executive Summary

II. Background

III. Other Seat Belt Reminder Requirements and Protocols

IV. Statutory Authority

V. Summary of the NPRM

VI. Final Rule and Response to Comments

A. Rear Seat Belt Warning Requirements

1. Applicability

2. Requirements

a. Visual Warning on Vehicle Start-Up

i. Type of Information Conveyed by the Visual Warning and Whether Occupant Detection Should Be Required

ii. Lack of an Audible Warning

iii. Triggering Conditions for Start-of-Trip Warning (Not Including Occupant Detection Criteria)

iv. Seat Occupancy Criteria and Interaction With Child Restraint Systems

v. Duration

vi. Other Aspects

b. Audio-Visual Change-of-Status Warning

c. Electrical Connections/Removable Seats

d. Owner's Manual Instructions

e. Telltale Location

3. Alternative Warning Signals

B. Front Seat Belt Warning Requirements

1. Applicability

2. Driver's Seat Belt Warning for Light Buses

3. Visual and Audible Warning Duration and Activation

4. Visibility of Visual Warning for Front Outboard Passenger Seat Belt

5. Front Seat Occupant Detection and Seat Occupancy Criteria

C. Issues Common to the Front and Rear Seat Belt Warning Requirements

1. Modification of Start-of-Trip Warning Trigger Related Ignition Switch Position To Accommodate EVs

2. Belt Use Criteria

3. Visual Warning Characteristics

4. Interaction With Other Vehicle Warnings

5. Audible Warning Characteristics (Other Than Duration)

6. Warning Deactivation and Acknowledgement and Hardening

7. Vehicles With Automated Driving Systems

8. Test Procedures

VII. Regulatory Alternatives

VIII. Overview of Benefits and Costs

A. Final Rule Requirements

1. Rear Seat Belt Warning System

2. Front Seat Belt Warning System

3. Overall Benefits and Costs of the Final Rule

B. Regulatory Alternatives

1. Occupant Detection in Rear Seats

2. 90-Second Front Outboard Seat Belt Warning

3. Seat Belt Warning for Front Center Seat

IX. Compliance Dates

X. Regulatory Analyses

Appendix A. List of Comments Cited in Preamble

I. Executive Summary

This final rule amends Federal Motor Vehicle Safety Standard (FMVSS or Standard) No. 208, “Occupant crash protection,” to require a seat belt use warning system for rear seats. This rule completes NHTSA's response to a mandate in the Moving Ahead for Progress in the 21st Century Act (MAP-21) that directed NHTSA to initiate a rulemaking to require a seat belt warning for the rear seats in motor vehicles; it also completes NHTSA's action on a rulemaking petition from Public Citizen and Advocates for Highway and Auto Safety for the same rule. The final rule also updates and enhances the current seat belt warning requirements for the driver's seat belt and extends these requirements to the front outboard passenger seat. The final rule applies (with some exceptions) to passenger cars, trucks, most buses, and multipurpose passenger vehicles (MPVs) with a gross vehicle weight rating (GVWR) of 4,536 kilograms (10,000 pounds) or less. NHTSA is issuing this final rule under the National Traffic and Motor Vehicle Safety Act (Safety Act), 49 U.S.C. chapter 301, Motor Vehicle Safety (49 U.S.C. 30101

et seq.

Safety Need for the Final Rule

Using a seat belt is one of the most effective ways a motor vehicle occupant can prevent death and injury in a crash. Seat belts prevent occupants from being ejected from the vehicle, provide “ride-down” by gradually decelerating the occupant as the vehicle deforms and absorbs energy, and reduce occupant contact with harmful interior surfaces and other occupants. Seat belts are effective in most types of crashes and

greatly reduce the risk of fatal and non-fatal injuries compared to the risk faced by unrestrained occupants.

While seat belt use is meaningfully higher than it was a decade ago, there is room for improvement. Usage rates for seat belts in rear seats have consistently been below those for the front seats; and while front seat belt use rates increased in the early 2010s, for the last several years they have plateaued. According to data from NHTSA's annual study of observed seat belt use, in every year from 2013 through 2022, seat belt use was lower in the rear seats than in the front seats, ranging from a difference of about 9 percentage points in 2013 (78 percent vs. 87 percent) to about 14 percentage points in 2017 (75 percent vs. 89 percent). In 2022, front seat belt use was about 91.6 percent and rear seat belt use was about 81.7 percent.

Every year, thousands of unrestrained motor vehicle occupants are killed in crashes and tens of thousands of unrestrained occupants are injured (additional details on the target population are provided in the summary of benefits and costs later in this executive summary). Seat belt warning systems (also referred to as seat belt reminder systems) encourage seat belt use by reminding unbuckled occupants to fasten their belts and/or by informing the driver that a passenger is unbelted so that the driver can request the unbelted occupant to buckle up. The warnings provided by seat belt warning systems typically consist of visual and/or audible signals. Research by NHTSA and others shows that seat belt warning systems are effective at getting unbuckled occupants to fasten their seat belts.

FMVSS No. 208 currently requires a short-duration audio-visual seat belt warning for the driver's seat belt in passenger cars, most trucks and MPVs with a GVWR of 4,536 kg (10,000 lb) or less, and buses with a GVWR of 3,855 kg (8,500 lb) or less. Under these current requirements, the visual component of the warning generally must be at least 60 seconds long, and the audible component must be at least four seconds long.

Voluntary adoption by vehicle manufacturers of warnings that go beyond this regulatory minimum, while considerable, has been mixed. Although the regulations do not require seat belt warnings for any seating position other than the driver's seat, almost all model year (MY) 2022 vehicles have a voluntarily provided seat belt warning for the front outboard passenger seat. However, voluntary adoption for rear seats has been much slower, as only about 47 percent of MY 2022 vehicles come equipped with a voluntarily provided rear seat belt warning system. Most vehicles already provide a seat belt warning for both front outboard seats that is much longer than the minimal required warning for the driver's seat belt, with the vast majority of vehicles including an alert that is at least 90 seconds. This widespread adoption suggests that the front seat belt warning minimum requirements in the FMVSS are outdated, as consumers accept audio-visual reminders that are far longer than the required minimums.

As discussed above, rear seat belt use rates have persistently been below those for the front seats, and progress on front seat belt use rates has slowed. Moreover, unbuckled occupants, in the front and rear seats, continue to be overrepresented in fatal crashes (51 percent), given the lower exposure of unbelted occupants relative to belted occupants (because front seat belt use is about 90 percent and rear seat belt use is 80 percent). Despite the effectiveness of seat belts and seat belt warnings, most new vehicles continue to lack a rear seat belt warning. Additionally, while most vehicles provide some level of enhanced reminders for the front seats, this level of enhanced protection has not occurred for all vehicles and is not standardized. This gap in protection suggests a need for a beneficial safety technology that is not being met in the vehicle market. This final rule is intended to meet this safety need.

Legal Authority and Prior Regulatory History

NHTSA is issuing this final rule pursuant to the National Traffic and Motor Vehicle Safety Act (49 U.S.C. 30101

et seq.

) (Safety Act), which authorizes NHTSA to establish FMVSSs. That statute requires safety standards to be objective, practicable, and meet the need for safety, among other things. NHTSA has concluded that the finalized requirements satisfy these statutory criteria.

This final rule completes NHTSA's response to a rulemaking mandate in MAP-21. MAP-21 required DOT (NHTSA, by delegation) to initiate a rulemaking proceeding to require rear seat belt warnings and directed the agency to issue a final rule unless the rule would not meet the Safety Act requirements for an FMVSS.

This final rule also completes NHTSA's action on a rulemaking petition from Public Citizen and Advocates for Highway and Auto Safety. The petition requested that NHTSA issue a rule requiring a seat belt warning system for rear seats on passenger cars and MPVs with a GVWR of 4,536 kg (10,000 lb) or less.

Summary of the Final Rule

This final rule amends the existing seat belt warning provisions in FMVSS No. 208. The final rule has two main components. The first requires a seat belt warning for the rear seats. The second amends and enhances the seat belt warning requirements for the front outboard seats. The requirements apply (with some exceptions) to passenger cars and trucks, most buses, and multipurpose passenger vehicles with a GVWR of 4,536 kg (10,000 lb) or less.

1. Rear Seat Belt Reminder Requirements

The first component of this final rule is a set of requirements for a seat belt warning for rear seats. The new requirements have four main elements.

•

Visual warning on vehicle start-up to inform the driver of the status of the rear seat belts.

The final rule requires a visual warning that informs the driver how many or which rear seat belts are in use and/or not in use. The warning must activate when the ignition (or, for electric vehicles (EVs), propulsion system) is activated, and last for at least 60 seconds. No visual warning is required if the system can determine that there are no occupied rear seats or if there are no occupied rear seats with a seat belt that is not in use.

•

Audio-visual change-of-status warning.

The final rule requires an audio-visual warning whenever a fastened rear seat belt is unfastened while the vehicle is in forward or reverse drive mode. (The warning is not required if the system can determine that a rear passenger has unfastened the seat belt in order to exit the vehicle or switch seats.) The warning must last for at least 30 seconds or until the seat belt that triggered the warning is re-fastened. The audible portion of the warning may be temporarily paused to allow another audible safety warning alerting the driver to take immediate action.

•

Requirements related to electrical connections.

Readily removable rear seats must either automatically establish the electrical connections when the seat is put in place or, if a manual connection is required, the connectors must be readily accessible. Vehicles equipped with certain types of seat belt warning systems are additionally required to provide a visual warning to the driver if a proper electrical connection has not been established.

•

Owner's manual requirements.

The vehicle owner's manual (which includes information provided by the vehicle manufacturer to the consumer, whether

in digital or printed form) must describe the warning system's features, including the location and format of the visual warnings. It must also include instructions on how to make any manual electrical connections for readily removable seats.

2. Front Outboard Seat Belt Warning Requirements

The final rule includes several changes and enhancements to the seat belt warning requirements for the front outboard seats. The new requirements have two main elements.

•

Seat belt warning now required for front outboard passenger seat.

This final rule requires a seat belt warning for the front outboard passenger seat. It does not require one for front center seats because, among other things, doing so would not be cost-effective. Currently, only the driver's seat is required to have a seat belt warning, although almost all vehicles now provide a seat belt warning for the front outboard passenger seat as well.

•

Enhanced audio-visual seat belt warning.

The final rule requires a longer-duration audio-visual warning than is currently required for the driver's seat belt. The final requirements for this warning differ from the proposal, which would have required (with some exceptions) an audio-visual warning lasting until the belt at any occupied front outboard seat was fastened. This included a warning at the start of a trip and if a belt was unfastened during a trip. The proposal did not include any other warning triggers, such as vehicle speed. The final rule requires a visual warning and a two-phase audible warning that is based, in part, on vehicle speed.

Visual warning.

Under the final rule, a visual warning is required whenever the ignition switch is in the “on” or “start” position (or the propulsion system is activated), the seat is occupied, and the seat belt is not in use. The warning must be visible to the driver.

Audible warning.

The final rule requires a two-phase audible warning. The first phase warning must activate when the ignition/propulsion system is activated, the seat is occupied, and the belt is not in use. The first phase warning must last for at least 30 seconds, unless the seat belt that triggered the warning is fastened or the second phase audible warning is activated within that time. The second phase audible warning must activate, and remain active, whenever the seat is occupied, the seat belt is not in use, and the vehicle speed is at least 10 km/h (6.2 mph). The audible warning may be temporarily paused to allow another audible safety warning alerting the driver to take immediate action.

The final rule also contains requirements for the visual and audible warnings as well as for other system features.

Compliance Date

This final rule establishes a compliance date for the amendments to FMVSS No. 208, “Occupant crash protection,” as follows. Manufacturers must comply with the amendments as of September 1, 2026 for the front seat belt warning system requirements and September 1, 2027 for the rear seat belt warning system requirements, with optional early compliance (see Section IX for details). Consistent with 49 CFR 571.8(b), multi-stage manufacturers and alterers have an additional year to comply.

Regulatory Alternatives

NHTSA considered a wide range of alternatives to the proposed requirements. The main alternatives NHTSA considered were the seat belt warning requirements in Economic Commission for Europe (ECE) Regulation No. 16 (R16) and Euro New Car Assessment Programme (Euro NCAP). The finalized requirements are identical or similar to ECE R16 and Euro NCAP in many respects but differ from them in several ways. For instance, while under ECE R16 the smallest occupant a rear seat belt system with occupant detection must be capable of detecting is a small-statured adult female, under the final rule such systems must be capable of detecting occupants as small as a 6-year-old child and activating the warning accordingly. Another way the proposal differs from ECE R16 is the duration of the front seat belt warning on vehicle start-up: R16 generally requires only a 30-60 second audio-visual warning; the final rule requires, under certain conditions, an audio-visual warning that lasts until the seat belt is buckled. The final regulatory analysis quantifies the costs and benefits of three specific regulatory alternatives: requiring occupant detection for the rear seat belt warning system; requiring (for the front outboard seats) an audio-visual warning on vehicle start-up with a duration of 90 seconds; and requiring a seat belt warning for front center seats.

Benefits and Costs of the Proposed Requirements

This final rule is significant and was reviewed by the Office of Management and Budget under Executive Order 12866, as amended by Executive Order 14094.

NHTSA estimates the target population and the benefits and costs of the final rule requirements in the stand-alone final regulatory impact analysis (FRIA) that is being placed in the docket with this final rule and is summarized in this document.

Based on NHTSA's data on fatalities and injuries from motor vehicle crashes, adjusted to account for the benefits of other mandatory safety technologies, there are, on average, 822 fatalities and 11,409 injuries to unrestrained rear seat occupants and 8,383 fatalities and 154,739 injuries to unrestrained front outboard seat occupants each year. The final rule requirements are aimed at reducing these deaths and injuries.

NHTSA estimates the benefits it expects from the final rule seat belt warning requirements. The benefits are the fatalities and injuries that would be prevented by these requirements. The benefits depend, principally, on the expected increase in seat belt use and the effectiveness of seat belts in preventing deaths and injuries.

For the rear seat belt warning system analysis, NHTSA used a “low” and a “high” estimate for the increase in rear belt use with the warning system. For occupants 11 years and older, these were 3 and 5 percentage points, respectively, and for occupants from 6 to 10 years old, 0.3 and 0.4 percentage points respectively.

For simplicity, NHTSA refers to these scenarios as “Low” and “High.” The estimated annual benefits for rear seat belt warning systems are presented in table 1.

Children in booster seats are part of the target population for this final rule because they should be restrained with the seat belt and so would benefit from a seat belt reminder. The transition to a booster seat typically occurs from ages 4-7 years, and recommendations to remain in a booster seat exist until age 12 years.

https://www.nhtsa.gov/vehicle-safety/car-seats-and-booster-seats#find-the-right-car-seat-car-seat-recommendations.

The Abbreviated Injury Scale (AIS) is a classification system for assessing impact injury severity developed and published by the Association for the Advancement of Automotive Medicine and is used for coding single injuries, assessing multiple injuries, or for assessing cumulative effects of more than one injury. MAIS represents the maximum injury severity of an occupant at an AIS level,

i.e.,

the highest single AIS for a person with one or more injuries. MAIS 1 & 2 injuries are considered minor injuries and MAIS 3-5 are considered serious injuries.

Table 1—Estimated Annual Benefits—Potential Lives Saved and Injuries Prevented for Rear Seat Belt Warning Systems (SBWS) Without Occupant Detection, With Estimated “Low” and “High” Percentage Point Increase in Belt Use

Injury level

Low

High

MAIS 1

MAIS 2

120

MAIS 3

MAIS 4

MAIS 5

Total Injuries

148

221

Fatal

Another way to measure benefits is by calculating equivalent lives saved (ELS). Equivalent lives saved are the number of prevented fatalities added to the number of prevented injuries, with the prevented injuries expressed in terms of fatalities (that is, with an injury expressed as a fraction of a fatality, so that the more serious the injury, the higher the fraction). The estimated equivalent lives saved assuming either a 3 percent or 7 percent discount rate are presented in table 2.

Table 2—Estimated Annual Benefits—Equivalent Lives Saved (ELS)—Rear SBWS Without Occupant Detection

Belt use increase

3 Percent

discount rate

7 Percent

discount rate

Low

29.98

24.31

High

45.09

36.55

NHTSA also estimates the costs of the final rule requirements for rear seat belt warnings. NHTSA estimates that the minimum cost to comply with the rear seat belt warning requirements is $166.44 million (M). This is based on a per-vehicle cost of $19.59 for 53.1 percent of 16M affected new vehicles.

Based on the foregoing, NHTSA performed benefit-cost and cost-effectiveness analyses. A benefit-cost analysis calculates the net benefits, which is the difference between the benefits flowing from injury and fatality reductions and the cost of the rule. The net benefit estimates are presented in table 3. The cost-effectiveness analysis derives the cost per equivalent life saved, which is equal to the total cost of the rule divided by the total fatal equivalents that it prevents. These estimates are presented in table 4.

Table 3—Net Benefits—Rear SBWS Without Occupant Detection

[2020 Dollars, in millions]

Belt use increase

Benefits

3 percent

discount

Benefits

7 percent

discount

Cost

Net benefits

3 percent

discount rate

Net benefits

7 percent

discount rate

Low

$357.78

$290.05

$166.4

$191.34

$123.62

High

538.00

436.16

166.4

371.56

269.72

Table 4—Cost-Effectiveness Analysis (Cost per Equivalent Life Saved)—Rear SBWS Without Occupant Detection

[2020 Dollars, in Millions]

Belt use increase

ELS 3

percent

discount

ELS 7

percent

discount

Cost

Cost/ELS

3 percent

discount

Cost/ELS

7 percent

discount

Low

29.98

24.31

$166.4

$5.55

$6.85

High

45.09

36.55

166.4

3.69

4.55

This final rule also enhances the driver seat belt warning requirements by requiring an indefinite visual warning and a two-phase audible warning that is based, in part, on vehicle speed that remains active until the driver's seat belt is buckled and extending these enhanced driver's seat belt warning requirements to the front outboard passenger seat. NHTSA estimates the annual benefits of a seat belt warning for the driver and outboard front passenger that remains active until the occupant's seat belt is buckled as shown in table 5 and table 6.

Table 5—Estimated Annual Benefits—Lives Saved and Injuries Prevented—Indefinite Duration SBWS (Front Outboard Seats)

Injury level

Driver

Front

passenger

Total

MAIS 1

129

143

MAIS 2

151

170

MAIS 3

MAIS 4

MAIS 5

Total Injuries

354

395

Fatal

Table 6—Estimated Annual Benefits—Equivalent Lives Saved—Indefinite Duration SBWS (Front Outboard Seats)

Undiscounted

3 Percent

discount rate

7 Percent

discount rate

Driver

42.26

34.98

28.36

Front Passenger

4.44

3.68

2.99

Total

46.70

38.66

31.35

NHTSA estimates that the incremental cost of the enhanced seat belt warning for the driver's seat and the front outboard passenger seat would be no greater than the currently available seat belt warning. Although a seat belt warning is currently not required for the front outboard passenger seats, we estimate that 96 percent of new vehicles are equipped with them.

NHTSA estimates that the cost for equipping a front outboard passenger seat with a seat belt warning system is about $2.13 per vehicle. To equip a seat belt warning system in the front outboard passenger seat positions on the remaining four percent of the new vehicle fleet (16 million) without such a warning is $1.36 million (= $2.13 × 0.04 × 16 million).

Based on data on total projected vehicle sales in the United States for MY 2022 from the agency's New Car Assessment Program

Purchasing with Safety in Mind: What to Look For When Buying a Vehicle

program.

The total monetized benefits, costs, and net benefits (total monetized benefits—total cost) of the enhanced seat belt warning system for the driver and front passenger are shown in table 7. Table 8 presents the results of the cost effectiveness analysis—cost per equivalent lives saved from enhanced SBWS for the driver and front outboard passenger.

Table 7—Annual Monetized Benefits, Costs, and Net Benefits—Indefinite SBWS (Front Outboard Seats)

[2020 Dollars, in Millions]

Driver

3 Percent

7 Percent

Front passenger

3 Percent

7 Percent

Driver and front

passenger

3 Percent

7 Percent

Passenger Car Benefits

$188.89

$154.12

$22.86

$18.65

$211.75

$172.77

Light Truck & Van Benefits

228.51

184.29

21.05

16.97

249.56

201.26

Total Benefits

417.41

338.41

43.90

35.62

461.31

374.03

Total Costs

1.36

Net Benefits

417.41

338.41

42.54

34.26

459.95

372.67

Table 8—Cost-Effectiveness Analysis (Cost per Equivalent Life Saved)—Indefinite SBWS (Front Outboard Seats)

[2020 Dollars, in millions]

Discount rate

ELS

Cost

Cost/ELS

3 percent

38.66

$1.36

$0.04

7 percent

31.35

1.36

0.04

The net benefits of the final rule requiring seat belt warning for rear seating positions and the enhanced seat belt warning for the front outboard seats are shown in table 9. The net benefits are positive for both 3 percent and 7

percent discount rates and for both the low and high effectiveness estimates for rear seat SBWS.

Table 9—Net Benefits From the Final Rule (SBWS Without Occupant Detection for Rear Seating Positions and Indefinite SBWS for Front Outboard Seating Positions)

[2020 Dollars, in millions]

3 Percent

discount rate

7 Percent

discount rate

Front Outboard Seats

$459.95

$372.67

Rear Seats (low increase in rear seat belt use)

191.34

123.62

Rear Seats (high increase in rear seat belt use)

371.56

269.72

Total Net Benefits (low increase in rear belt use)

651.29

496.28

Total Net Benefits (high increase in rear belt use)

831.51

642.39

II. Background

On September 7, 2023, NHTSA published a notice of proposed rulemaking (NPRM) to amend FMVSS No. 208, “Occupant crash protection,” to require a seat belt use warning system for rear seats and to enhance the existing front seat belt warning requirements, including requiring a seat belt warning for the front outboard passenger seat and increasing the duration of the warning.

This section provides an abbreviated background on the subject matter and regulatory history of the proposed requirements. For a fuller discussion, the reader is referred to the NPRM.

88 FR 61674.

Id.

at pgs. 61680-61686.

Seat Belts and Seat Belt Warning Systems

Using a seat belt is one of the most effective actions a motor vehicle occupant can take to prevent death and injury in a crash.

Seat belts protect occupants in various ways. They prevent occupants from being ejected from the vehicle, gradually decelerate the occupant as the vehicle deforms and absorbs energy, and reduce the occurrence of occupant contact with harmful interior surfaces and other occupants.

Research has found that seat belts greatly reduce the risk of fatal and non-fatal injuries compared to the risk faced by unrestrained occupants. For rear seat occupants, seat belts reduce the risk of fatality by 55 percent (for passenger cars) and 74 percent (for light trucks and vans). For drivers, seat belts reduce the risk of fatality by 48 percent (for passenger cars) and 61 percent (for light trucks and vans) and reduce the risk of moderate to greater severity injuries by 65 percent. For front outboard passengers, seat belts reduce the risk of fatality by 37 percent (for passenger cars) and by 58 percent (for light trucks and vans) and reduce the risk of moderate to greater severity injuries by 65 percent.

See, e.g.,

68 FR 46262 (Aug. 5, 2003). See

also

Buckling Up: Technologies to Increase Seat Belt Use. Special Report 278 at 18, Committee for the Safety Belt Technology Study, Transportation Research Board of The National Academies (2003).

Charles J. Kahane, Lives Saved by Vehicle Safety Technologies and Associated Federal Motor Vehicle Safety Standards, 1960 to 2012—Passenger Cars and LTVs—With Reviews of 26 FMVSS and the Effectiveness of Their Associated Safety Technologies in Reducing Fatalities, Injuries, and Crashes. 89 DOT HS 812 069 at 89, Department of Transportation, National Highway Traffic Safety Administration (2015).

See the Final Regulatory Impact Analysis (FRIA) (in the docket for this rulemaking) for these effectiveness estimates.

While seat belt use is meaningfully higher than it was a decade ago, there is room for improvement. Usage rates for rear seat belts have consistently been below those for the front seats, and while front seat belt use rates increased early in the previous decade, for the last several years they have plateaued. According to data from NHTSA's National Occupant Protection Use Survey (NOPUS), from 2013 to 2022, seat belt use was lower in the rear seat than in the front seat, ranging from a difference of 8.8 percentage points in 2013 (78.3 percent vs. 87.1 percent) to 14.3 percentage points in 2017 (75.4 percent vs. 89.7 percent).

In 2022, front seat belt use was 91.6 percent and rear seat belt use was 81.7 percent.

See Figure 1.

Boyle, L.L. (2022, August). Occupant restraint use in 2021: Results from the NOPUS Controlled Intersection Study (Report No. DOT HS 813 344). National Highway Traffic Safety Administration. NOPUS is the only nationwide probability-based observational survey of seat belt use in the United States. The survey observes seat belt use as it actually occurs at randomly-selected roadway sites, and involves a large number of occupants (68,804 in 2021). NOPUS observations are made during daylight hours and are not necessarily representative of high-risk driving times when belt use may be lower.

Boyle, L.L. (2023, November). Occupant restraint use in 2022: Results from the NOPUS Controlled Intersection Study (Report No. DOT HS 813 523). National Highway Traffic Safety Administration.

ER03JA25.000

NHTSA has, over time, implemented a variety of strategies to increase seat belt use. These have included sponsoring national media campaigns, supporting the enactment of state seat belt use laws and high-visibility enforcement, and facilitating or requiring vehicle-based strategies.

While such measures have helped make enormous progress, the persistent gaps in seat belt use suggest that additional approaches may be necessary.

For example, NHTSA runs a Congressionally mandated High Visibility Enforcement annual campaign focused on increasing seat belt use. The Click It or Ticket nationwide campaign has been in effect for about 20 years. It runs every year from mid-May through the Memorial Day weekend, into the first week in June.

Seat belt warning systems (also referred to as seat belt reminder systems) are a vehicle-based strategy to increase belt use. Seat belt warning systems encourage seat belt use by reminding unbuckled occupants to fasten their belts and/or by informing the driver that a passenger is unbelted, so that the driver can request the unbelted occupant buckle up. The warnings provided by seat belt warning systems typically consist of visual and audible signals. An optimized warning system balances effectiveness and annoyance, so that the warning is noticeable enough that the occupants will be motivated to fasten their belts, but not so intrusive that an occupant may attempt to circumvent or disable it or the public will not accept it. Research by NHTSA and others shows that seat belt warning systems are effective at getting unbuckled occupants to fasten their seat belts. (We take a closer look at this research in Section VIII, Overview of Benefits and Costs, and the FRIA.)

See

also Section V of the NPRM (pgs. 61684-61685).

FMVSS No. 208 currently requires a short audio-visual seat belt warning for the driver's seat belt on passenger cars;

trucks and MPVs with a GVWR of 4,536 kg (10,000 lb) or less (except for some compliance options which do not require the warning);

and buses with a GVWR of 3,855 kg (8,500 lb) or less and an unloaded weight less than or equal to 2,495 kg (5,500 lb).

The standard does not require seat belt warnings for any seating position other than the driver's seat.

S4.1.5.1(a)(3); S7.3.

S4.2.6; S7.3.

S4.2.6 (with the exception of some compliance options).

See, e.g.,

Interpretation Letter from NHTSA to R. Lucki, July 24, 1985 (“Thus, the intent was to require a warning system for only the driver's position.”). All NHTSA interpretation letters cited in this preamble are available at

https://www.nhtsa.gov/nhtsa-interpretation-file-search.

Manufacturers have two compliance options for the driver's warning.

The first option requires that if the key is in the “on” or “start” position and the seat belt is not in use, the vehicle must provide a visual warning for at least 60 seconds, and an audible warning that lasts 4 to 8 seconds. Under the second option, when the key is turned to the “on” or “start” position, the vehicle must provide a visual warning for 4 to 8 seconds (regardless of whether the driver seat belt is fastened) and an audible warning lasting 4 to 8 seconds if the driver seat belt is not in use.

The current seat belt warning requirements (

i.e.,

for the driver's seat only) have been in the standard since 1974.

49 CFR 571.208, S7.3.

The warning requirements for automatic belts in S4.5.3 mirror, with some differences, the first compliance option. Automatic belts are rarely, if ever, installed in current production vehicles, and NHTSA's regulations limit the seating positions for which automatic belts may be used to rear seats.

39 FR 42692 (Dec. 6, 1974).

Although not required by NHTSA's regulations, most currently produced vehicles have a seat belt warning for the front outboard passenger seat. Based on data on total projected vehicle sales in the United States for MY 2022 from the agency's New Car Assessment Program (NCAP)

Purchasing with Safety in Mind: What to Look For When Buying a Vehicle

program, almost all (about 97 percent) MY 2022 vehicles offered for sale in the United States were equipped with a seat belt warning for the front outboard passenger seat.

Further, almost all vehicles already provide an audio-visual seat belt warning for both front outboard seats that is longer than the minimum warning for the driver's seat belt currently required in FMVSS No. 208. However, the persistence of the front seat belt warning, while often greater than the minimal durations required by FMVSS No. 208, is not consistent across new vehicles. Specifically, a little over half of MY 2022 vehicles provide a visual warning that lasts until the belts at any occupied front outboard seat are fastened, and almost all (about 93 percent) have an audible warning lasting at least a minute and a half; however, less than half have an audible warning lasting at least two minutes.

This means that while many new vehicles have significantly enhanced reminders, many do not. This disparity, along with the plateauing front seat belt use numbers, suggests that the current regulatory minima are

too short, and that in the absence of a requirement, persistent audible reminders that could improve front seat belt use are not widely available in the market.

22 23 24

Through the NCAP program, NHTSA sends annual requests for safety information about new vehicles to vehicle manufacturers. This includes specific questions on seat belt reminder systems. The focus of this request for information is for vehicle models that will be sold in the upcoming model year that have a GVWR of 4,536 kg (10,000 lb) or less, and this data generally covers all such vehicles offered for sale in the U.S. for MY 2022. Throughout this document we will refer to this data as our “NCAP data” or “Purchasing with Safety in Mind: What to Look For When Buying a Vehicle” data or information.

See

NPRM, pgs. 61709-61711, and appendix A.

Mark Freedman

et al.

The Effectiveness of Enhanced Seat Belt Reminder Systems Draft Report: Observational Field Data Collection Methodology and Findings. 2007. DOT HS-810-844. Washington, DC: National Highway Traffic Safety Administration.

N. Lerner

et al.

2007. Acceptability and Potential Effectiveness of Enhanced Seat Belt Reminder System Features. DOT HS 810 848. Washington, DC: National Highway Traffic Safety Administration [hereinafter DOT 2007.

Transportation Research Board Study at 8, 25; Mark Freedman et al., Effectiveness and Acceptance of Enhanced Seat Belt Reminder Systems: Characteristics of Optimal Reminder Systems Final Report. DOT HS 811 097.

While almost all MY 2022 vehicles have a seat belt warning for the front outboard passenger seat, under half come equipped with a rear seat belt warning system. Rear seat belt warnings were first introduced in the United States by Volvo around 2009. About 47 percent of MY 2022 vehicles, from 15 vehicle manufacturers, are equipped with a rear seat belt warning system. Thus, while rear seat belt warnings have become more widely deployed in recent years, the majority of the current fleet still is not equipped with them.

In short, front seat belt use rates appear to have plateaued, and rear seat belt use rates have persistently been below those for the front seats. Moreover, unbuckled occupants continue to be overrepresented in fatal crashes (51 percent), given the lower exposure of unbelted occupants relative to belted occupants (because front seat belt use was about 90 percent and rear seat belt use was 80 percent for the period in question). In spite of the effectiveness of seat belts and seat belt warnings, most new vehicles continue to lack a rear seat belt warning, and, while many vehicles provide significantly enhanced reminders for the front seats, many do not. This suggests a need for a beneficial safety technology that is not being met in the vehicle market. This final rule is intended to meet that need.

Rulemaking Petition, MAP-21 Mandate, and Prior Rulemaking Notices for This Action

On November 21, 2007, Public Citizen and Advocates for Highway and Auto Safety (Advocates, and, collectively, petitioners) petitioned NHTSA to amend FMVSS No. 208 to require a seat belt warning system for rear seats on passenger cars and MPVs with a GVWR of 4,536 kg (10,000 lb) or less.

On June 29, 2010, the agency published a Request for Comments document (RFC) on the petition.

The RFC discussed the agency's research and findings regarding rear seat belt warnings and solicited comments. NHTSA subsequently granted the petition.

Docket No. NHTSA-2010-0061-0002.

75 FR 37343 (June 29, 2010) (Docket No. NHTSA-2010-0061).

In 2012, Congress passed the Moving Ahead for Progress in the 21st Century Act (MAP-21).

That legislation contained two provisions regarding seat belt warning systems. First, it repealed the 8-second durational limit for the driver's seat belt audible warning.

Second, it required the Secretary of Transportation to initiate a rulemaking proceeding to amend FMVSS No. 208 to provide a safety belt use warning system for designated seating positions in the rear seat.

It directed the Secretary to either issue a final rule, or, if the Secretary determines that such an amendment does not meet the requirements and considerations of 49 U.S.C. 30111,

to submit a report to Congress describing the reasons for not prescribing such a standard.

Public Law 112-141 (2012).

Id.

at section 31202(a)(2) (repealing portion of 49 U.S.C. 30124).

Id.

at section 31503. Authority has been delegated to NHTSA. 49 CFR 1.95.

Section 30111 requires that a Motor Vehicle Safety Standard meet the need for safety, be stated in objective terms, and be practicable, among other requirements.

See infra

Section IV.

In 2019, NHTSA published an Advance Notice of Proposed Rulemaking (ANPRM) seeking comment on a variety of issues related to potential rear seat belt warning requirements.

NHTSA published the NPRM on September 7, 2023.

84 FR 51076 (Sept. 27, 2019) (Docket No. NHTSA-2019-0093).

88 FR 61674.

III. Other Seat Belt Reminder Requirements and Protocols

The Economic Commission for Europe (ECE) has instituted seat belt warning requirements, and the European New Car Assessment Programme (Euro NCAP) and the Insurance Institute for Highway Safety (IIHS) have also included seat belt reminder systems in their respective ratings protocols. Below we briefly summarize the seat belt reminder provisions in each of these.

ECE Requirements

The ECE has issued an updated version of Regulation No. 16

(R16) that requires seat belt reminder systems in all front and rear seats on new cars.

The seat belt reminder system is required to have both a start-of-trip warning and a change-of-status warning for both the rear and front seats, though the exact requirements differ somewhat for rear and front seats.

ECE Regulation No. 16, Revision 10.

The regulation was introduced in two phases: September 1, 2019 for new vehicle types (

i.e.,

all vehicle models with a new type approval) and September 1, 2021 for all newly-produced and registered vehicles.

Rear seat requirements.

R16 specifies a two-level warning. The first-level warning is a visual warning and the second-level warning is an audio-visual warning. The first-level warning applies at the start of a trip and the second-level warning applies when a fastened belt becomes unfastened during a trip. The first-level warning must activate when the seat belt of any of the rear seats is not fastened and the ignition switch or master control switch is activated. The first-level warning must last at least 60 seconds or until the belt is fastened (or the seat is no longer occupied, if equipped with occupant detection). The second-level warning must activate when a belt becomes unfastened and certain specified speed or distance thresholds are met and must last for 30 seconds unless other specified criteria are met (

e.g.,

the belt is re-fastened).

Front seat requirements.

The front seat belt warning requirements are similar to the rear seat warnings, with some differences. First, the first-level visual warning is only required to last 30 seconds, not 60 seconds. Second, the second-level audio-visual warning applies to unfastened belts at the start of the trip as well as to changes in belt status (

i.e.,

a fastened belt that becomes unfastened).

The regulation also contains a variety of other requirements relating to the seat belt warning systems (

e.g.,

telltales, exemptions for certain vehicles and seating positions). R16 also allows for short- and long-term deactivation of both front and rear warnings.

The ECE requirements are discussed in more detail where relevant in later sections of this preamble.

Euro NCAP

Euro NCAP introduced seat belt warnings in their assessment protocol in 2002. The Euro NCAP protocol for Safety Assist systems describes which features a seat belt reminder must have to qualify for points in this area of assessment,

which is then used to calculate the overall vehicle rating.

Euro NCAP's overall safety rating is based on four areas of assessment (Adult Occupant Protection, Child Occupant Protection, Vulnerable Road Users, and Safety Assist).

European New Car Assessment Programme Assessment Protocol—Safety Assist, Safe Driving, Version 10.3, December 2023.

Rear seat warnings.

For rear seats, a visual signal must start once the ignition switch is engaged. The visual signal must be at least 60 seconds long. Occupant detection is required for rear seats to be eligible for a score; this is a new requirement that was instituted after NHTSA published the NPRM. For systems without occupant detection,

the visual signal must clearly indicate to the driver which seat belts are in use and not in use. For systems with occupant detection on all rear seating positions, the visual signal does not need to indicate the number of seat belts in use or not in use, but the signal must remain active if a seat belt remains unfastened on any of the occupied seats in the rear. No visual signal is required if all the rear occupants are belted. For systems with rear seat occupant detection, a 30-second audible signal needs to activate before the vehicle reaches a speed of 25 km/h (15.5 mph) or before it travels 500 meters when any occupied seat has an unbuckled belt. When any seat belt experiences a change of status at vehicle speeds above 25 km/h (15.5 mph), an audio-visual signal is required, with the visual signal lasting 60 seconds and the audible warning lasting 30 seconds, unless certain conditions are met.

This language remains in the protocol as a precondition for receiving a score for seats with occupant detection. In a vehicle where not all the rear seats are equipped with occupant detection, if seats without occupant detection do not meet these requirements the seats with occupant detection would not receive a score.

Front seat warnings.

The Euro NCAP protocol requires that, to receive points, at the start of a trip the system must provide a visual seat belt warning that lasts until the belt is fastened

and an audible warning that activates when certain conditions are met and generally must last at least about 90 seconds (the exact duration depends on a variety of specified criteria, such as vehicle speed or distance travelled). It also specifies an audio-visual change-of-status warning that meets the requirements of the initial start-of-trip warning.

Section 3.4.2.1.

Insurance Institute for Highway Safety (IIHS) Protocol

On December 2021, IIHS released its Seat Belt Reminder System Test and Rating protocol.

It sets out general requirements for the seat belt reminder visual and audible signals for front outboard and rear seating positions. It specifies that a visual signal must be displayed in the instrument panel, overhead panel, or center console, indicating an unfastened belt. The audible warning must begin if the seat belt is unfastened at ignition and for change-of-status, and can cease when the seat belt is unfastened, the vehicle is no longer in motion, or the seat is no longer occupied. The protocol also has sound pressure level and frequency requirements for the audible warning.

Insurance Institute for Highway Safety. (April 2024.) Seat Belt Reminder System Test and Rating Protocol, Version III,

available at https://www.iihs.org/media/f15e5be9-ac62-4ea6-a88d-7511105bfff5/H3hGKQ/Ratings/Protocols/current/Seat%20Belt%20Reminder%20Test%20Protocol.pdf

(

last accessed

May 16, 2024).

For the rear seats, the IIHS protocol specifies that the visual signal must activate within 10 seconds of the ignition being turned on, that the signal must indicate whether the seat belt at each rear seating position is fastened or unfastened, and that it must last at least 60 seconds. It does not require a visual signal if the seat belts at all occupied rear seats are fastened or if no rear occupants are present. It allows the visual signal to be cancelled by the driver. For a seat belt change-of-status in the rear seats when the vehicle is in motion, it requires an audible and visual signal that lasts at least 30 seconds. It further specifies that the audible and visual signal can stop when seat belts at the occupied rear seats are fastened, the vehicle is no longer in motion, or the seats are no longer occupied.

For the front seats, under the IIHS ratings protocol, the primary audible reminder signal for the front outboard seats must be at least 90 seconds in total duration to obtain an “acceptable” or “good” rating.

Unlike Euro NCAP, the IIHS rating system provides ratings (Poor, Marginal, Acceptable, and Good) instead of points. For instance, if the front-passenger seat has an audible signal that lasts less than 8 seconds it would be given a “Poor” rating. For a “Good” rating both the driver and front-passenger belt reminder must have an audible signal that lasts at least 90 seconds and meet the rest of the belt reminder system requirements for an “Acceptable” rating, including the requirements for a rear seat belt reminder system. Accordingly, a vehicle cannot receive a “Good” rating without having a rear seat belt reminder system, and a rear seat belt reminder system is not required for all the other ratings. The protocol does not specify occupancy criteria (that is, the smallest occupant (or the size and weight corresponding to the smallest occupant)) that the system must be able to detect.

IV. Statutory Authority

NHTSA is issuing this final rule pursuant to its authority under the National Traffic and Motor Vehicle Safety Act (Safety Act). Under 49 U.S.C. chapter 301, Motor Vehicle Safety (49 U.S.C. 30101

et seq.

), the Secretary of Transportation is responsible for prescribing motor vehicle safety standards. The responsibility for promulgation of FMVSS is delegated to NHTSA.

See

49 CFR 1.95.

Section 30111 of the Safety Act requires that an FMVSS be practicable, meet the need for motor vehicle safety, and be stated in objective terms.

The Safety Act defines “motor vehicle safety” as “the performance of a motor vehicle or motor vehicle equipment in a way that protects the public against unreasonable risk of accidents occurring because of the design, construction, or performance of a motor vehicle, and against unreasonable risk of death or injury in an accident, and includes nonoperational safety of a motor vehicle.”

“Motor vehicle safety standard” means a minimum performance standard for motor vehicles or motor vehicle equipment.

When prescribing safety standards, the Secretary must consider all relevant, available motor vehicle safety information.

The Secretary must also consider whether a proposed standard is reasonable, practicable, and appropriate for the types of motor vehicles or motor vehicle equipment for which it is prescribed, and the extent to which the standard will further the statutory purpose of reducing traffic accidents and associated deaths.

49 U.S.C. 30111(a).

49 U.S.C. 30102(a)(9).

Section 30102(a)(10).

Section 30111(b)(1).

Section 30111(b)(3)-(4).

The statutory criterion of practicability is multidimensional. Most relevant to this rule, it means that in issuing this final rule, NHTSA must balance benefits and costs, with safety as the preeminent consideration.

This requirement means that NHTSA ought not simply choose the least costly regulatory option.

It also means that

the final rule must be reasonably feasible, both economically

and technologically.

Importantly, however, the Safety Act does allow NHTSA to issue technology-forcing safety standards.

NHTSA must also consider the public acceptability of safety standards

and provide adequate lead time.

See, e.g., Motor Vehicle Mfrs. Ass'n of U.S., Inc.

State Farm Mut. Auto. Ins. Co.,

463 U.S. 29, 55 (1983) (“The agency is correct to look at the costs as well as the benefits of Standard 208 . . . When the agency reexamines its findings as to the likely increase in seatbelt usage, it must also reconsider its judgment of the reasonableness of the monetary and other costs associated with the Standard. In reaching its judgment, NHTSA should bear in mind that Congress intended safety to be the preeminent factor under the Motor Vehicle Safety Act.”).

See, e.g., Public Citizen, Inc.

Mineta,

340 F.3d 39, 58 (2nd Cir. 2003) (“The notion that `cheapest is best' is contrary to

State Farm.

There the Court instructed NHTSA `to look at the costs as well as the benefits' of motor vehicle safety standards, and to “bear in mind that Congress intended safety to be the pre-eminent factor under the [Safety Act.] Thus, when NHTSA issues

standards under the Safety Act,

State Farm

requires that the agency weigh safety benefits against economic costs; moreover,

State Farm

instructs the agency to place a thumb on the safety side of the scale.”) (

quoting Motor Vehicle Mfrs. Ass'n of U.S., Inc.,

463 U.S. at 54) (citations omitted).

See, e.g., Public Citizen, Inc.

Mineta,

340 F.3d at 58 (2nd Cir. 2003) (“The committee recognizes . . . that the Secretary will necessarily consider reasonableness of cost, feasibility and adequate lead time.”) (quoting H. Rep. No. 1776, at 16 (1966)).

See, e.g., Paccar, Inc.

Nat'l Highway Traffic Safety Admin.,

573 F.2d 632, 635 n.5 (9th Cir. 1978) (“Practicable is defined to require consideration of all relevant factors, including technological ability to achieve the goal of a particular standard[.]”) (citations and quotations omitted) (quoting H.R. Rep. No. 1776, 89th Cong., 2d Sess. 16 (1966)).

Chrysler Corp.

Dep't of Transp.,

472 F.2d 659, 673 (6th Cir. 1972) (“[T]he Agency is empowered to issue safety standards which require improvements in existing technology or which require the development of new technology, and it is not limited to issuing standards based solely on devices already fully developed.”).

Pac. Legal Found.

Dep't of Transp.,

593 F.2d 1338, 1345-46 (D.C. Cir. 1979) (“We believe that the agency cannot fulfill its statutory responsibility unless it considers popular reaction. Without public cooperation there can be no assurance that a safety system can meet the need for motor vehicle safety.”) (quotations and citations omitted).

2 U.S. Code Cong. & Adm. News, 89th Cong., 2d Sess., 1966, p. 2714,

quoted in H & H Tire Co.

U. S. Dep't of Transp.,

471 F.2d 350, 353 (7th Cir. 1972). (“The committee recognizes . . . that the Secretary will necessarily consider [in the issuance of standards] reasonableness of cost, feasibility and adequate lead time.”).

In developing this final rule, the agency carefully considered these statutory requirements and has concluded that it meets them. They are discussed in more detail throughout the preamble and in the regulatory analyses where relevant.

V. Summary of the NPRM

The NPRM had two main components. The first proposed requiring a seat belt reminder for the rear seats. The second proposed changes and enhancements to the seat belt warning requirements for the front outboard seats, most notably an audio-visual warning that persists until the seat belt at any occupied front outboard seat is fastened. These proposed requirements would apply to passenger cars and trucks, buses (except school buses), and MPVs with a GVWR of 4,536 kg (10,000 lb) or less.

Rear Seat Belt Reminder Requirements

The first component of the NPRM was a set of proposed requirements for a seat belt warning for rear seats. The proposed requirements had four main elements.

•

Visual warning on vehicle start-up to inform the driver of the status of the rear seat belts.

We proposed three different compliance options from which manufacturers could choose for the rear seat belt warning system. The first would require the system to indicate how many or which rear seat belts are in use (the “positive-only” option). The second would require the system to indicate, for the occupied rear seats, how many or which rear seat belts are not in use (the “negative-only” option). The third would require the system to indicate, for the occupied rear seats, how many or which rear seat belts are in use and how many or which rear seat belts are not in use (the “full-status” option). Certain features would be required of all the options. Each system would have to provide a continuous or flashing visual warning, consisting of either icons or text, visible to the driver. The visual warning would have to last for at least 60 seconds, beginning when the vehicle's ignition switch is moved to the “on” or “start” position. All the systems would require that the vehicle be equipped with technology to determine that the belt latch is fastened.

The negative-only and full-status compliance options would additionally have required that the vehicle be equipped with an occupant detection system (which facilitates these more informative warnings).

We note the preamble language imprecisely indicated the necessity for a belt latch sensor. As discussed later in this document, it was not our intention to require a specific technology.

•

Audio-visual change-of-status warning.

We proposed an audio-visual warning whenever a fastened rear seat belt is unfastened while the ignition switch is in the “on” or “start” position and the vehicle's transmission selector is in a forward or reverse gear. The warning would have to last for at least 30 seconds. We did not propose any requirements for the volume or tone of the warning. The intent of this warning was to alert the driver or other occupants to a change in belt status during a trip. The warning would not be required if a door is open, which would be the case if a rear passenger unfastened their belt in order to exit the vehicle.

•

Requirements related to electrical connections.

We proposed to require that readily removable rear seats either automatically re-establish the necessary electrical connections, or, if a manual connection is required, have readily accessible connectors. Further, vehicles with the negative-only compliance option would be required to provide a visual warning to the driver if a proper electrical connection has not been established for a readily removable rear seat.

•

Owner's manual requirements.

We proposed that the vehicle owner's manual (which includes information provided by the vehicle manufacturer to the consumer, whether in digital or printed form) describe the warning system's features (including the location and format of the visual warnings) and include instructions on how to make any manual electrical connections for readily removable seats.

Front Outboard Seat Belt Warning Requirements

The NPRM included several enhancements to the seat belt warning requirements for the front outboard seats. We proposed three main changes.

•

Audio-visual warning on vehicle start-up for front outboard passenger seat.

We proposed to require a seat belt warning for the front outboard passenger seat.

•

Increasing the duration of the audio-visual warning on vehicle start-up.

We proposed enhancing the front seat warning requirements by requiring an audio-visual warning that remains active until the seat belt at any occupied front outboard seat is fastened. Vehicle manufacturers could adjust the characteristics of the auditory warning signal (such as frequency and volume) to make the warning both effective and acceptable to consumers. The proposal included specific duty cycle characteristics.

•

Audio-visual change-of-status warning.

We also proposed to require an audio-visual change-of-status warning whenever a front outboard seat belt is unbuckled during a trip (unless a front door is open, to account for an occupant unfastening the belt to exit the vehicle). The warning would be required to remain active until the seat belt is refastened.

Proposed Compliance Date

We proposed a compliance date for the amendments to FMVSS No. 208, “Occupant crash protection,” as follows. Manufacturers would be required to comply with the amendments as of the first September 1 that is one year after the publication of the final rule for the front seat belt warning system requirements and the first September 1 that is two years after the publication of the final rule for the rear seat belt warning system requirements, with optional early

compliance. Multi-stage manufacturers and alterers would have an additional year to comply.

Regulatory Alternatives

NHTSA considered alternatives to the proposed requirements. The main alternatives NHTSA considered were the seat belt warning requirements in ECE R16 and Euro NCAP. The proposed requirements were identical or similar to ECE R16 and Euro NCAP in many respects but differed from them in several ways. For instance, while the ECE rear seat belt warning regulations allow a warning for an unfastened seat belt at an unoccupied seat, the proposal would not allow this, because we tentatively believed that the resulting “false” warning would potentially annoy drivers and lead to behaviors that would decrease system effectiveness. Another way the proposal differed from ECE R16 is the duration of the front seat belt warning on vehicle start-up: R16 generally requires only a 30-60 second audio-visual warning; NHTSA proposed a warning that lasts until the seat belt is buckled.

VI. Final Rule and Response to Comments

A. Rear Seat Belt Warning Requirements

1. Applicability

The proposal applied to all rear designated seating positions in passenger cars and all rear designated seating positions certified to a compliance option requiring a seat belt in trucks, buses, and MPVs with a GVWR of 4,536 kg (10,000 lb) or less, except for school buses and law enforcement vehicles. NHTSA's regulations define a bus as a vehicle designed for carrying more than ten persons.

The proposal included small buses, which refers to buses with a GVWR not more than 10,000 lb; this therefore includes high-capacity vans. However, the proposal did not include medium-sized buses (with a GVWR 10,000 lb-26,000 lb) or large buses (with a GVWR greater than 26,000 lb). We proposed to apply the proposed requirements to the specified categories of vehicles because these vehicles are required to have seat belts at all rear designated seating positions and (except for some buses) a seat belt warning for the driver's seat. We noted that some types of trucks and MPVs (motor homes, walk-in van-type trucks, vehicles designed to be sold exclusively to the U.S. Postal Service, or vehicles with a GVWR between 8,500-10,000 lb carrying a chassis-mount camper)

and over-the-road buses that are also prison buses

are not required to have rear seat belts. In the NPRM we explained that we did not propose to exempt special-purpose vehicle types such as ambulances because NHTSA believed that they are typically customized after first sale.

49 CFR 571.3 (“

Bus

means a motor vehicle with motive power, except a trailer, designed for carrying more than 10 persons.”) (italics in original).

S4.2.7.1.

S4.4.3.3; S4.4.5.1.

The proposed applicability was largely consistent with ECE R16, with a few differences. The rear seat belt reminder requirements in R16 do not include vehicles that carry more than nine persons (including the driver).

There is also no weight specification for the passenger vehicles to which R16 applies. R16 also exempts “ambulances, hearses, and motor-caravans as well as for all seats for vehicles used for transport of disabled persons, vehicles intended for use by the armed services, civil defense, fire services and forces responsible for maintaining public order.”

Section 8.4.1.2 (rear seat belt warning requirements apply to M

and N

category vehicles); Consolidated Resolution on the Construction of Vehicles (R.E.3) Revision 6, Section 2.2.1 (category M

vehicles) (“Vehicles used for the carriage of passengers and comprising not more than eight seats in addition to the driver's seat.”) and Section 2.3.1 (category N

vehicles) (“Vehicles used for the carriage of goods and having a maximum mass not exceeding 3.5 tonnes [7,716 lb].”).

Section 8.4.1.3.

Comments

NHTSA received comments that supported the proposal; comments that recommended expanding the applicability; and comments that recommended excluding additional vehicle types.

Some commenters specifically supported various aspects of the proposal. Freedman Seating Company (FSC) and Mr. Koo supported the vehicles covered by the proposal and Ms. Tombrello supported including van-like buses because she believed some have been prone to misloading of passengers and baggage. Mr. Stange agreed that the final rule should exclude medium and large buses, due to the distraction the system would create for the driver; problems with maintenance and sensor reliability; and the fact that bus passengers are not required to wear seat belts in some states.

Some commenters argued for including additional higher-capacity vehicles that the proposal excluded. The National Safety Council (NSC) and Ms. Tombrello supported including school buses (regardless of weight) and Mr. Koo supported including school buses with a GVWR 10,000 lb and under. FSC supported extending the requirements to over-the-road buses with a GVWR between 10,000 and 26,000 lb (except school, perimeter seating and transit buses). NSC commented that the final rule should include limousines. Relatedly, InterMotive Vehicle Controls (InterMotive) commented that it manufactures an aftermarket seat belt reminder system for buses and vans with a GVWR both below and above 10,000 lb.

On the other hand, some comments argued for excluding additional vehicles from the requirements. The Alliance for Automotive Innovation (Auto Innovators) and Mercedes-Benz and Mercedes-Benz Research and Development North America (Mercedes) recommended exempting vehicles with more than six rear seats or more than two rear rows, pointing to challenges with providing the driver with the status information on all seating positions via the instrument panel (or other in-vehicle display) due to the number of seats that may need to be displayed. Auto Innovators further commented that for high-occupancy vehicles with removeable seats, an electronic control unit and other hardware are needed, which leads to practicability concerns, including increased costs for customers. Mercedes reiterated these practicability concerns.

The Recreational Vehicle Industry Association (RVIA) similarly commented that this final rule should harmonize with R16 and not apply to motor homes. RVIA raised several different issues specific to motor homes. First, it explained that motor homes are used in unique ways because they are used both for transportation and for temporary, recreational, and seasonal use. As an example, RVIA discussed a scenario where occupants are seated in a rear seating position with the motor home turned on, but where the vehicle remains stationary, leading to a false warning. Second, it commented that motor homes' rear seats are often used for storage, which could again lead to false warnings. Third, RVIA commented that, because motor homes are often equipped with non-conventional seats that convert into a bed, developing wiring and sensors that would not be damaged in the conversion process would be challenging if not impossible. Fourth, RVIA commented that the rear portion of a motor home also has its own electrical system with very little interface with the chassis electronics. This lack of interface between electrical systems is unique in comparison to other types of vehicles that typically have seats installed in standard

configurations in the same factory as the vehicle is assembled, completed, and shipped. RVIA stated that there is currently not a way to provide electronic signals from the seating positions in the rear portion of the motor home to the sophisticated electronics controls that are proprietary to the chassis manufacturers.

Finally, Braun Northwest (BNW) commented that the final rule should exempt ambulances, giving essentially two different reasons. First, BNW commented that the reason NHTSA gave for not exempting ambulances—that they are typically customized after first sale—was factually inaccurate. BNW commented that while some special-purpose vehicles may be customized after first sale, that is not the case with ambulances. BNW explained that data from the Ambulance Manufacturer's Division of the National Truck Equipment Association indicates that van ambulances with a GVWR under 10,000 lb, which would be affected by this NPRM, comprise more than 20 percent of the annual production of United States ambulance manufacturers. Second, BNW pointed out that, while circuited buckles needed for seat belt buckle status indication are commonly available and simple to install on the two- and three-point seat belts commonly used on most vehicles, they are inherently problematic on the four, five, and six-point belts needed on ambulances. BNW explained that recent work facilitated by NHTSA resulted in a new SAE International (SAE) recommended practice, SAE J3026 Ambulance Patient Compartment Seating Integrity and Occupant Restraint, developed specifically for testing occupant restraint systems in ambulances. All three national ambulance standards (KKK-A-1822F, Federal Specification: Star-Of-Life Ambulance; NFPA 1917 Standard for Automotive Ambulances; and CAAS Ground Vehicle Standard) now require compliance with SAE J3026. BNW indicated that the critical ramification of SAE J3026 for the NPRM was that side-facing ambulance bench seats must be fitted with four-point, five-point, or six-point seat belts. BNW commented that there are practicability concerns with enabling buckle status indication for these seat belts, including the problem of getting wires from an emergency locking seat belt retractor to a circuited buckle located at the center front of the occupant's torso. Additionally, BNW argued that seat belt reminders may prevent medical personnel from administering medical care, as changes in occupant position required to render patient care would cause alarm indications that add distraction and confusion in an environment where such distractions can have dire consequences.

Agency Response

NHTSA is adopting the proposal except that the final rule contains an additional exemption for ambulances.

The major difference between the vehicles to which R16 and the final rule apply is that the final rule applies to small buses, which typically include buses with up to about four rear rows—mainly high-capacity passenger vans (10 to 15-passengers), such as Chevrolet Express, Ford Transit, GMC Savana, and Mercedes Sprinter passenger vans. However, because the rule applies only to vehicles with a GVWR less than 10,000 lb, it would generally not include vehicles with more than four rows.

We believe that including small buses such as these high-capacity vans addresses an important safety need. As we explained in the NPRM, we believe it is particularly important to include vehicles with a GVWR greater than 3,855 kg (8,500 lb), but less than or equal to 4,536 kg (10,000 lb), because this range includes high-occupancy vehicles. Including these vehicles is important because an increasing number of high-occupancy vehicles are used as personal vehicles and are not solely used for work-related purposes.

In addition, multiple rear seats or rows make it more difficult for the driver to ascertain rear seat belt use, so a warning could prove especially useful in these vehicles. We think this requirement would be especially beneficial for 15-passenger vans, for which there is both an increased risk of rollover (related to the occupancy level of these vehicles) and lower seat belt use rates compared to other passenger vehicles.

See, e.g., https://media.ford.com/content/fordmedia/fna/us/en/news/2016/07/29/nothing-mini-about-this-van--ford-transit-attracts-large-familie.html

(

last accessed

May 16, 2024).

Belt use rates among occupants in 15-passenger vans involved in fatal crashes are significantly lower compared to other passenger vehicles. See Subramanian, R. (2008). Fatalities to Occupants of 15-Passenger Vans, 1997-2006. (Report No. DOT-HS 810 947). National Highway Traffic Safety Administration.

Providing a reminder in vehicles with multiple rear rows is technically feasible. As we noted above, because the final rule applies to vehicles with a GVWR 10,000 lb or less, it generally would not include vehicles with more than four rear rows of seats, which should make it easier to implement a reminder. We are unaware of any currently produced full-size passenger vans having a rear seat belt reminder system. We did find aftermarket solutions from abroad for medium to large buses,

and InterMotive commented that a seat belt warning system already exists for multipurpose passenger vehicles with a GVWR both below and above 10,000 lb. They currently manufacture an after-market solution, SeatLink, for the bus and van market, including seats supplied by Freedman Seating Company (Freedman). However, we do not have any information on the performance and reliability of these systems.

See https://www.phoenixseating.com/our-products/all-buckled-up

and

https://www.fsrtek.com/applications/bus-seat-belt-alarm-system

(

last accessed

May 16, 2024).

We do acknowledge that vehicles such as high-capacity vans may encounter visual signal complexities. Accordingly, our intent was to propose performance requirements that provide manufacturers with the flexibility to design a warning system that is appropriate for each vehicle type (for example, the final rule does not require a full schematic of the rear seats). For example, a visual warning option for vehicles with multiple rows could be the seat belt icon with an adjacent number corresponding to how many rear seat belts are fastened. In addition, as we explain in more detail below (see Section VI.A.2.a.i), in response to the comments, we have expanded the compliance options to allow additional types of visual warning systems. This too should help address any concerns related to feasibility.

The final rule, however, also follows the proposal in excluding school buses and medium and large buses. As we explained in the NPRM, extending the requirements to school buses would place additional cost burden on school systems and may result in reductions in service; would place additional burdens on the driver; and raises liability issues and the potential for buses being out of service due to malfunctioning systems. Many of these concerns were raised by commenters to the ANPRM and we believe these concerns are still valid. Moreover, as we also pointed out in the NPRM, school buses use compartmentalization, which provides protection even to unbelted occupants. Similarly, the final rule also excludes medium and large buses because of issues such as those noted by Mr. Stange, including cost, reliability, and driver burden.

The final rule also follows the proposal by including motor homes. As an initial matter, we note that some motor homes are not required to have

rear seat belts so the requirements will not necessarily apply to all motor homes. In addition, the seat belt requirements do not apply to seats in motor homes with a GVWR over 10,000 lb and classified as MPVs which the manufacturer designates and conspicuously labels as not intended for occupancy while the vehicle is in motion.

Accordingly, such vehicles are not subject to the requirements in this rule. Although we recognize that R16 exempts motor homes (motor caravans), we see no reason to exclude from this rule designated seating positions (DSPs) in motor homes that are required to have seat belts. Those DSPs are designed to have passengers while the vehicle is in motion. Such occupants would benefit from a seat belt and therefore, from a seat belt reminder. We note that if the motor home is turned on for other purposes than driving, the start-up warning is a 30-second visual warning that should not be unduly annoying.

49 CFR 571.3 (definition of “designated seating position”); FMVSS No. 207 S4.4.

Limousines, depending on their characteristics, may also be covered by the rule. Limousines are not currently a vehicle class defined in the FMVSS. Depending on its characteristics, a limousine might be classified as a passenger car, MPV, or bus.

Generally, a passenger car is designed for carrying 10 or fewer persons, an MPV is a vehicle carrying 10 or fewer persons which is constructed either on a truck chassis or with certain special features, and a bus is designed to carry more than 10 persons. The final rule encompasses all these vehicle types, so a limousine would be covered by the requirements as long as it weighed 10,000 lb or less. At the same time, the FMVSS generally apply to new vehicles, including new vehicles that are altered, or vehicles manufactured in more than one stage. Limousines (such as “stretch” limousines) that are the result of modifications made to a vehicle after first purchase other than for resale would not be required to be certified to the seat belt reminder requirements for seating positions that are added in the modification process.

49 CFR 571.3.

The Infrastructure, Investment and Jobs Act, H.R. 3684, Sections 23015, 23023 (117th Congress) (2021), contains two provisions that direct NHTSA to conduct research and issue rules (if such rules would meet the criteria in section 30111 of the Safety Act) related to various aspects of limousine crashworthiness and occupant protection. NHTSA's research in these areas is ongoing.

See, e.g.,

DOT Regulatory Agenda, Fall 2023, RIN 2127-AM48, “Seat Belts in Limousines,”

available at https://www.reginfo.gov/public/do/eAgendaViewRule?pubId=202310&RIN=2127-AM48

(

last accessed

December 16, 2024). The law also directs that the rules issued pursuant to it apply to modified vehicles. However, that law also defines the term “limousine” to, among other things, refer to vehicles weighing between 10,000 and 26,000 lb. This would therefore not include any limousines that are covered by this final rule, which is limited to vehicles up to 10,000 lb. GVWR.

The one way the final rule does depart from the proposal with respect to the applicability is by including an exemption for ambulances from the rear seat belt warning system requirements.

Given the information provided by BNW, the original intent of the rule not applying to ambulances, and the fact that excluding ambulances harmonizes with ECE R16, the final rule exempts ambulances. Although neither FMVSS No. 208 nor 49 CFR 571.3 defines “ambulance,” FMVSS No. 201, “Occupant protection in interior impact,” defines it to mean “a motor vehicle designed exclusively for the purpose of emergency medical care, as evidenced by the presence of a passenger compartment to accommodate emergency medical personnel, one or more patients on litters or cots, and equipment and supplies for emergency care at a location or during transport.”

We are including a cross-reference to this definition in the regulatory text. However, we have not included a broader carve-out for emergency vehicles. We did not receive any comments indicating that such a carve-out was necessary. Moreover, there are a number of ways that owners and purchasers of emergency vehicles for official purposes could disable the warnings. These owners and purchasers already sometimes alter vehicles significantly.

This does not exempt ambulances from the front seat belt warning requirements.

FMVSS No. 201, S3 (definitions).

Although section 30122 of the Safety Act prohibits making inoperative required safety devices, this prohibition does not apply to vehicle owners.

See infra

n. 91 and accompanying text.

2. Requirements

The NPRM proposed a 60-second visual warning on vehicle start-up; a 30-second audio-visual warning if a buckled belt is unfastened during a trip; and requirements or criteria related to readily removable seats, the owner's manual instructions, the location of the telltale, and how NHTSA would determine that a belt was or was not in use. We discuss these requirements in turn below.

a. Visual Warning on Vehicle Start-Up

The NPRM proposed a 60-second visual warning on vehicle start-up that would inform the driver of how many or which seat belts are and/or are not in use. We proposed three different compliance options for the type of information conveyed to the driver. Occupant detection would not be required for one of the three compliance options. The warning would be triggered when the ignition is placed in the “on” or “start” position. When testing a system certified to one of the compliance options necessitating occupant detection, NHTSA would seat a dummy or human occupant corresponding to a 6-year-old. We discuss these proposed requirements below in more detail.

i. Type of Information Conveyed by the Visual Warning and Whether Occupant Detection Should Be Required

The proposed requirements for the rear seat belt warning system (RSBWS) included a visual warning that would activate on vehicle start-up to inform the driver of the status of the rear seat belts. We proposed three different compliance options. The first would require the system to indicate how many or which rear seat belts are in use (the “positive-only” option). The second would require the system to indicate, for the occupied rear seats, how many or which rear seat belts are not in use (the “negative-only” option). The third would require the system to indicate, for the occupied rear seats, how many or which rear seat belts are in use and how many or which rear seat belts are not in use (the “full-status” option). The negative-only and full-status compliance options would require that the rear seats be equipped with a mechanism to determine when a belt latch is fastened and an occupant detection system (which facilitates these more-informative warnings), while the positive-only option would only require that the rear seats be equipped with a mechanism to determine when a belt latch is fastened.

In the NPRM we stated that we had tentatively decided not to require occupant detection in the rear seats because occupant detection continued to present technical challenges which could reduce the effectiveness and/or acceptance of these systems. This tentative decision was also based on factors such as the needed increase in seat belt use for this regulatory alternative to have positive net benefits. Because we did not propose to require occupant detection, we also did not propose requiring enhanced warnings (such as an audible warning on vehicle start-up).

The proposal harmonized with ECE R16 and Euro NCAP in a variety of ways, but also deviated from them in some respects.

ECE R16 requires a visual warning at the start of a trip. That warning “indicate[s] at least all rear seating positions to allow the driver to identify, while facing forward as seated on the driver seat, any seating position in which the safety-belt is unfastened.”

Occupant detection is not required, but in vehicles that do have occupant detection the warning does not need to indicate unfastened belts for unoccupied seating positions.

Section 8.4.4.2.

The Euro NCAP rating protocol also requires a visual warning at the start of a trip. The requirements are similar to ECE R16. However, Euro NCAP's rating protocol was recently revised to require occupant detection in the rear seat to receive points for this feature. For systems without occupant detection, the visual signal must clearly indicate to the driver the seating positions showing the rear seat belts in use and not in use. (These seats would not be eligible for points, but in order for seats with occupant detection to receive points the seats without occupant detection would have to meet these requirements.) For systems with occupant detection, the visual signal does not need to indicate the number of seat belts in use or not in use, but the signal must remain as long as the seat belt remains unfastened on any of the occupied seats in the rear.

No signal is required if all of the rear occupants are belted

or no rear occupants are detected.

Section 3.4.3.1.3.

Section 3.4.3.1.4.

Section 3.4.3.1.1.

The IIHS rating protocol requires a visual signal indicating “whether the seat belt at each rear seating position is fastened or unfastened.”

Seat Belt Reminder System Test and Rating Protocol, Version III at pg. 7.

The NPRM acknowledged that the proposed compliance options were not consistent with all seat belt warning systems currently deployed in the U.S. and Europe or with Euro NCAP's requirements. Specifically, we noted that manufacturers appeared to be deploying systems that would be categorized as either positive-only or negative-only except without occupant detection, the latter of which would not be permitted under the proposed compliance options. We also noted that the positive-only compliance option did not appear to be consistent with Euro NCAP because Euro NCAP requires that systems without occupant detection show the rear seat belts in use and not in use, and the positive-only compliance option would not permit a visual signal for an unfastened seat belt.

Accordingly, while we tentatively concluded that the proposed compliance options would help mitigate false warnings and the possibly attendant consumer acceptance issues, we explained that we were considering altering the proposed compliance options to accommodate systems that are currently being deployed, or that manufacturers may wish to deploy in the future.

Comments

Auto Innovators, General Motors (GM), American Honda Motor Co. (Honda), and Hyundai America Technical Center, Inc. (HATCI) generally supported including multiple compliance options in the final rule. Freedman, Automotive Safety Council (ASC), Tesla, Advocates and Public Citizen, and the National Automobile Dealers Association (NADA) generally supported the proposed compliance options, although as noted below some of these commenters preferred certain compliance options or requested that additional compliance options be added.

Several commenters (Consumer Reports, Safe Kids Worldwide (SKW), Paradise, NSC, Safe Ride News (SRN), Cross, and Ms. Tombrello) argued that NHTSA should require occupant detection in the rear seats. Other commenters (Freedman, IEE,

ASC), while not explicitly recommending that occupant detection be required, either preferred options requiring occupant detection or focused on the benefits and feasibility of rear-seat occupant detection. These commenters made a variety of arguments.

A supplier of automotive sensing systems.

Some commenters argued that the necessary technology for occupant detection is feasible. Consumer Reports commented that occupant detection does not pose unreasonable technical challenges, and is not prohibitively expensive (see Section VIII, Overview of Costs and Benefits). Consumer Reports and Mr. Paradise commented that rear-seat occupant detection technology is already widely available; Mr. Paradise also noted that 7 percent of vehicles already have the technological capability of occupant detection in rear seats. NSC commented that challenges with false positives (

e.g.,

transportation of cargo and pets) can be addressed through a relatively small investment, such as with low-cost 2-D or digital cameras, and that costs would further decrease over time if it were required. Consumer Reports noted that occupant detection is already widely deployed in the front outboard passenger seats. Relatedly, although not recommending that occupant detection be required, IEE commented that today's occupant detection sensors, predominantly designed for a detection of 5th percentile adult female, can reliably differentiate occupants from cargo.

Several commenters focused on the benefits of requiring occupant detection. Consumer Reports, Mr. Paradise, SKW, SRN, ASC, Ms. Cross, NSC, and Ms. Tombrello commented that warning systems using occupant detection would be more effective than those without it. Consumer Reports, Paradise, Ms. Cross, and NSC noted that occupant detection would enable enhanced warnings, which are more effective.

Accordingly, some of these commenters recommended requiring the proposed full-status and/or negative-only options that required occupant detection. Consumer Reports argued that NHTSA should require the full-status compliance option because the “positive-only” and “negative-only” compliance options are insufficient to incentivize rear seat belt use. Consumer Reports commented that the positive-only option would be the least technically complex, but it would also be the least effective type of warning system (because it creates unnecessary mental work for the driver and allows room for human error). Consumer Reports further explained that the positive-only system would be a departure from Euro NCAP, which requires that systems without occupant detection show both the rear seat belts in use and those not in use. Consumer Reports also commented that given that both the negative-only and the full-status options require a belt latch sensor and an occupant detection system, the negative-only option should be eliminated because the full-status option is more informative and effective. SRN, ASC, NSC, and Ms. Cross similarly commented that NHTSA should require negative-only or full-status systems, which would be more effective in alerting caregivers to an unbuckled rear passenger than “positive-only” systems. Ms. Cross commented that negative-only and full-status systems can inform the driver whether any rear seat occupants are unbuckled without having to make a comparison between number of seats to the number of occupants and an audible component can be added. ASC also noted that permitting only negative-only and full-status systems would harmonize with the requirements in Europe.

Consumer Reports, Cross, and SKW also recommended requiring occupant detection because that feature could eventually be used for other safety functions such as rear occupant alerts for vehicular heatstroke prevention and air bag suppression. SKW and Ms. Cross pointed to the potential to detect children or other vulnerable occupants in child safety seats, booster seats, or seat belts.

On the other hand, vehicle manufacturers commented that the final rule should not require occupant detection. Toyota Motor North America, Inc. and Toyota Motor Corporation (Toyota) and Auto Innovators commented that an occupant detection system can introduce false positives. Several manufacturers requested removing the requirement for occupant detection from one or both of the proposed compliance options that required it (full-status and negative-only).

Toyota argued that NHTSA should allow negative-only systems without occupant detection because an occupant detection system does not provide any additional safety benefit for the negative-only system. Toyota explained that it is reasonable to anticipate that a driver knows whether a rear occupant is in the vehicle, and, as with a positive-only system, can combine that knowledge with the information from the visual indicator. Toyota also commented that a telltale indicating a seat belt is not fastened at an unoccupied seat is not a false positive, but is instead useful information for the driver.

More generally, several manufacturers and trade groups (Auto Innovators, Ford Motor Company (Ford), Nissan North America (Nissan), NADA, Honda, Hyundai Motor Company (Hyundai)) commented that NHTSA should permit manufacturers to convey information on positive belt status information (

i.e.,

when belt is in use) and/or negative belt status information (

i.e.,

when the belt is not in use) without occupant detection—that is, NHTSA should expand the proposed compliance options to permit negative-only systems without occupant detection and/or full-status systems without occupant detection.

NADA argued that these options would provide better contextual information for drivers than the proposed full‐status option because they would provide seat belt status information for all seating positions regardless of occupancy. Nissan, Ford, and Auto Innovators argued that presenting information on the seat belt status regardless of whether the seat is occupied or not should not be deemed as misleading but rather as furnishing the driver with pertinent contextual information concerning seat belt usage across all positions. Nissan and Ford argued that this information would empower the driver to distinguish easily between buckled and unbuckled seat belts, particularly when compared to the locations where known passengers are situated in the rear row. Auto Innovators, Nissan, NADA and Ford commented that this approach would be consistent with European regulations. Nissan, NADA, and Ford indicated that this approach would align with ECE R16, and Ford and Auto Innovators commented that the approach aligns with the IIHS approach. Honda commented that systems without occupant detection that provide visual information on both fastened and unfastened seat belts have been in use in Europe for many years and are well understood by those that use it regularly. Auto Innovators and NADA commented that not expanding the compliance options in this way would require development and deployment of new systems and increase cost and lead time for some original equipment manufacturers (OEMs), which ultimately harms consumers and hinders achievement of NHTSA's safety objective. Auto Innovators further commented that it was unaware aware of any data that would support NHTSA's claim that a visual indication of an unfastened seat belt at an unoccupied seat would annoy drivers and argued that if driver annoyance is a concern, NHTSA should consider allowing a dismissible initial warning, as is the case with both IIHS and R16.

Some of the comments were ambiguous with respect to whether they were referring to full-status systems, negative-only systems, or both.

In addition, Ford, Toyota, and Honda raised concerns with the proposed positive-only compliance option. Ford and Toyota commented that it conflicts with R16 and the IIHS protocol. Honda commented that if all rear occupants are unbuckled and there is no indication of their status, the driver may remain unaware of the system's ability to support the determination of the statuses of the belts for the rear occupants.

Agency Response

In response to the comments, the final rule follows the proposal in not requiring occupant detection, but modifies the proposal by revising the requirements to allow full-status and negative-only reminder systems without occupant detection.

The final rule follows the proposal in not requiring that rear seat belt reminder systems be equipped with occupant detection. There are a few reasons for this decision.

One reason is that we believe rear-seat occupant detection continues to present technical challenges. This is especially the case because we have concluded that rear-seat occupant detection systems should be able to detect, at a minimum, occupant characteristics matching a 6-year-old for determining whether a rear seat is occupied. This standard differs from ECE R16 and Euro NCAP, both of which base their requirements for occupant detection-equipped rear seat belt reminder systems on the 5th percentile female. This difference is discussed in more detail in Section VI.A.2.a.iv, Seat Occupancy Criteria and Interaction with Child Restraint Systems. Rear-seat belt reminder systems with occupant detection have only been recently deployed in vehicles sold in the U.S. (starting in MY 2021 based on our available data) and are currently offered on only a small proportion of new vehicles.

Based on the projected sales for MY 2022, approximately 7 percent of vehicles were equipped with rear-seat occupant detection. We have no data on how the occupant detection in these vehicles is working.

NHTSA does not have any specific information on the size of occupant these systems are designed to detect. However, based on the manufacturer comments requesting that NHTSA require occupant detection systems to detect a 5th percentile female occupant, it is likely that these systems are designed to detect occupants as small as the 5th percentile female.

While occupant detection technology is readily available and standard equipment in most front outboard passenger seats, the occupant detection technology used for the front outboard passenger seat does not necessarily translate directly to the rear seats. By comparison, vehicles subject to advanced air bag requirements comply using either suppression or low-risk deployment for different size child dummies, including the 6-year-old child dummy, in the front outboard passenger seat. Vehicles with a suppression system use some type of occupant detection technology in addition to other inputs (

e.g.,

seat belt use, seat position, etc.) to determine whether or not to deploy the air bag. Vehicles using low-risk deployment, however, do not necessarily need to use occupant detection to meet the advanced air bag requirements for that option. The vast majority of vehicles use the suppression option in the front outboard passenger

seat for at least one child dummy, and therefore use occupant detection.

77 78

There is also an option to use a dynamic automatic suppression system. To date, no manufacturer has attempted to certify using this option.

With respect to the driver's seat, while it is subject to certain advanced air bag requirements, those particular requirements do not necessitate occupant detection.

Vehicle manufacturers that opt to use a rear seat belt warning system with occupant detection will have to develop and implement occupant detection solutions that work for the unique seat designs and configurations found in rear seats (

e.g.,

bench seats, folding seats, different types of seat cushions, etc.) and validate the performance to ensure that they meet the new requirements and mitigate the potential for false positives. Among other challenges, rear seats create more potential for false positives than the front seats. As we explained in the NPRM and ANPRM, while occupant detection can reduce false warnings for unoccupied seats, it can also result in false warnings, due to the limitations of the sensors and different use scenarios in the rear seats (

e.g.,

transportation of cargo and pets). In addition, rear seats may be less well-defined than front seats (most rear seat rows, unlike the front seat rows, are comprised of three closely spaced seating positions), which could impede accurate detection. This deficiency could negatively affect consumer acceptance and/or effectiveness.

Another reason the final rule does not require occupant detection is that it adds non-trivial costs to the seat belt warning system. While we agree with Consumer Reports that rear-seat occupant detection is not prohibitively expensive in the sense that this is true for some vehicle lines, our cost-benefit analysis shows that occupant detection would be cost-beneficial only if rear seat belt use increased substantially more than we estimate it would for a warning system without occupant detection. Our teardown analysis indicates that occupant detection components cost $39.74 per vehicle, which, added to the $19.59 per vehicle cost of the buckle sensor, results in a combined warning system cost of $59.33 per vehicle (2020 $). We estimate that the total new fleet cost of a rear seat belt warning system with occupant detection would be about $802 million (2020 $). With respect to benefits, there is uncertainty with respect to how much more effective systems with occupant detection are compared to systems without it. Because of this uncertainty, our regulatory analysis does not attempt to estimate the net benefits or cost-effectiveness of rear seat belt reminder systems that use an occupant detection system. The regulatory analysis does, however, include a break-even analysis for a rear seat belt reminder system that requires occupant detection. For benefits and costs to break even (be equal) for this regulatory option, seat belt use for rear seat occupants 11 years and older would need to increase by approximately 5.2 percent when discounted at 3 percent and 6.4 percent when discounted at 7 percent. Furthermore, NHTSA considered the increase in seat belt use for rear seat occupants that would be required to match the net benefits under the final rule, which does not require occupant detection. When discounted at three and seven percent, seat belt use for rear seat occupants 11 years and older would need to increase by 6.43 percent to 8.57 percent to match the net benefits (taking into account the Low and High estimates) under the final rule. This is about two to three times greater than that estimated for the compliance option without occupant detection. (For more details, see Section VIII.B.1 and the FRIA.) Accordingly, while we agree with the commenters who supported a requirement for occupant detection because there may be benefits to having occupant detection (such as facilitating enhanced or more effective warnings)

and would expect some potential increase in seat belt use from that specific functionality, an effectiveness increase of this order of magnitude seems unlikely. Therefore, we do not expect this regulatory alternative to be net beneficial and would not generate the same level of net benefits as the final rule. Manufacturers may voluntarily equip vehicles with occupant detection if they so choose. Our hope is that over time, as the systems evolve and penetrate the fleet, the technology will mature and per-unit costs will decrease.

With respect to SKW's comments about the benefits of monitoring children in forward- or rear-facing CRSs, as we explained in the NPRM, children restrained by child restraint systems are not part of the target population for this rule.

With respect to the comment from Mr. Paradise concerning what he believed was an inconsistency between NHTSA's statements that a single-digit percentage of vehicles with rear-seat occupant detection being a small percentage of the fleet, and weighing in favor of not requiring it, and a single-digit percentage of vehicles with an indefinite reminder being non-trivial and supporting our proposal to require an indefinite reminder for the front seat belt start-of-trip warning, we do not believe these statements are inconsistent. In the context of occupant detection, we are referring to technological feasibility and likely regulatory cost; in the front seat belt warning section, we are referring solely to the optimum duration, as there is no question about feasibility. That is, a single-digit percentage has a different meaning in the two contexts.

Because we have decided not to require occupant detection, we disagreed with commenters who recommended requiring one or both of the proposed options that required occupant detection (full-status with occupant detection or negative-only with occupant detection). We continue to believe, as we explained in the NPRM, that while the full-status system (with occupant detection) does provide the driver with the most information, the other allowable types of systems, including those without occupant detection, will provide the driver with sufficient information to easily determine whether and where there are any unbuckled occupants and request that they fasten their seat belts.

Accordingly, the final rule allows the proposed positive-only option. These systems, while not providing information on the occupancy status of each seat, do provide information on which seat belts are buckled. The driver can combine this information with knowledge of the other occupants in the vehicle and determine if there are any unbuckled occupants and request them to fasten their belts. While this does require mental work on the part of the driver, and may not be as effective as a full-status system, we believe it is not so burdensome as to render such systems ineffectual to such a degree that we see a basis for prohibiting them. While such systems are not permitted under ECE R16 or Euro NCAP, manufacturers could select another type of system if they wished to harmonize with those protocols. (The positive-only system without occupant detection does conform with the IIHS protocol.) With respect to Honda's comment that the proposed positive-only option could potentially leave the driver unaware that the vehicle was equipped with a seat belt reminder system, we acknowledge that is a possibility, but it would not be a long-term problem. This would be limited to times when a driver is driving a vehicle new to them (unless the driver always reads owner's manuals first) and would only be an issue until a rear passenger buckles up. Once a rear passenger buckles up the driver would become aware of the existence of the warning.

We have modified the proposal so that the final rule does not dictate

specific compliance options for the information conveyed by the visual warning; the finalized requirements for the visual warning allow all of the systems that would have been allowed under the proposed rule, as well as additional systems that would not have been allowed under the proposal, such as a negative-only system without occupant detection, and a full-status system without occupant detection. Both the negative-only system without occupant detection and the full-status system without occupant detection are consistent with ECE R16 and the IIHS protocol (they would not be eligible for points under Euro NCAP). One factor underlying this choice is the lack of firm research data that could lead NHTSA to meaningfully compare the effectiveness of the different types of systems,

coupled with the fact that rear seat belt reminder systems conforming to the finalized requirements have already been deployed on vehicles sold in the United States.

These factors make us reluctant to prohibit particular design choices and inhibit manufacturer flexibility and ability to optimize system characteristics. We believe that the finalized regulatory text (“A visual warning indicating how many or which rear seat belts are in use and/or not in use must activate when the ignition switch is placed in the `on' or `start' position (or upon manual activation of the propulsion system, but prior to the vehicle being placed in “possible active driving mode” as defined by FMVSS No. 305))”

includes all of the systems manufacturers are currently deploying, but is specific enough to be objective and enforceable. For example, if there is one rear occupant, and that occupant is belted, a positive-only system without occupant detection that accurately indicates one buckled rear belt, and a full-status system with occupant detection that accurately indicates one rear occupant with a fastened belt, would both comply with the finalized regulatory text.

See

Mark Freedman et al., Effectiveness and Acceptance of Enhanced Seat Belt Reminder Systems: Characteristics of Optimal Reminder Systems Final Report. DOT HS 811 097 at pg. 49 (Feb. 2009) (hereinafter “DOT 2009 Seat Belt Study”).

An exception is a positive-only system with occupant detection, which is not prohibited by the finalized requirements and has yet to be deployed on vehicles sold in the United States. However, we believe it would be unlikely that a manufacturer would deploy such a system because the presence of occupant detection allows for more informative reminders—for example, a full-status reminder—than provided by a positive-only system. This is reflected in the fact that while we are aware of production versions of positive-only systems without occupant detection, negative-only and full-status systems with and without occupant detection, we are not aware of any vehicle equipped with both occupant detection and a positive-only reminder system.

The language relating to EVs is discussed in Section VI.C.1.

We agree with Toyota and Honda that the negative-only system requires the same cognitive effort on the part of the driver as the proposed positive-only option, and that it would still be effective and beneficial, even without occupant detection. We no longer agree with the view we expressed in the NPRM that such a signal is a false positive that might either desensitize the driver to the warning signal or lead them to circumvent or defeat the system. We now agree with Toyota that this is instead more accurately considered relevant information on seat belt status that the driver can use to determine whether there are any unbuckled occupants and request them to fasten their seat belts.

We reached a similar conclusion with respect to full-status systems without occupant detection. As we discussed above for the negative-only systems without occupant detection, we agree that while this system does not provide as much information as would a system with occupant detection, the information it does provide on the seat belt status at every seating position (occupied or not) is useful information for the driver. We also agree with the commenters who argued that allowing this option would support the introduction of systems that are already in widespread use, without adding in additional cost and complexity.

ii. Lack of an Audible Warning

The NPRM recognized that warnings with an audible component are generally more effective than visual-only warnings. However, we also recognized that requiring an audio-visual warning would necessitate requiring occupant detection because, without occupant detection, an audible warning would activate every time a rear seat is empty. These “false positives” would annoy the driver (as well as other occupants) and would decrease the effectiveness of the warning. Thus, the NPRM did not propose an audible warning on start-up. However, manufacturers would be free to provide an audible warning on start-up if they so choose. This approach is also consistent with ECE R16, Euro NCAP, and IIHS.

Comments

Many of the commenters who supported requiring occupant detection also supported requiring an audible warning (NSC, Consumer Reports, SRN, Karleigh Cross, and an anonymous commenter). SRN, Consumer Reports, and Ms. Cross commented that audible warnings are more effective than visual-only warnings. Consumer Reports also commented that requiring an audible component to the rear seat start-up warning would also make start-up warnings more consistent throughout a vehicle, regardless of the seating position.

Agency Response

The final rule does not require a rear seat audible start-of-trip warning, for the reasons articulated in the proposal. Because the final rule does not require occupant detection in the rear seats, it does not require an audible warning. We acknowledge that audio-visual warnings are more effective than visual warnings alone, and we believe that consumers would accept them. However, we believe that a visual warning alone will still be effective. While we cannot precisely estimate effectiveness, we have used a three to five percent belt use rate increase range (“lower” and “higher” scenario) in our analysis based on the available research. This analysis is explained in detail in the FRIA. We agree that in general, consistency between the rear reminder and front reminder requirements (which do require an audio-visual start-of-trip warning) is desirable, but do not believe that not requiring an audible component to the rear start-of-trip warning will create an issue in practice. In this context, the relevant potential concern with this inconsistency is that the driver—the recipient of the warning—would be confused or annoyed by any differences in the two warnings. Ultimately, we do not believe this inconsistency is a significant problem. The front seat belt warnings have been in vehicles for many years. Rear seat belt warnings will be new to most drivers, so drivers will have to become accustomed to them. In addition, the rear reminder will be a fairly prominent visual warning. If the driver is unsure of how the warnings operate, this rule also requires that the owner's manual include an accurate and easily understandable description of system features and operation.

iii. Triggering Conditions for Start-of-Trip Warning (Not Including Occupant Detection Criteria)

The NPRM proposed that the rear seat start-of-trip warning (which, as discussed above, is only required to be a visual warning) activate when the ignition switch is placed in the “on” or “start” position, except for negative-only systems when there are no occupied rear seats with a seat belt not

in use (for which we proposed that a warning not be required to activate). The activation criteria were modeled on the existing driver seat belt warning requirements and are also similar to those in ECE R16, Euro NCAP, and the IIHS protocol.

ECE R16 requires that the rear seat belt visual warning activate when a belt is not fastened and the ignition or master control switch activated.

It also provides that for vehicles with rear seat occupant detection, the visual signal does not need to indicate unfastened belts at unoccupied seats.

Section 8.4.2.3.1.

Section 8.4.4.2.

Euro NCAP similarly requires that the warning “`start' at the commencement of each `journey' that the vehicle makes.”

More specifically, the Euro NCAP protocol specifies that the visual signal be activated “when the ignition switch is engaged (engine running or not) and a seatbelt is not fastened.”

However, Euro NCAP allows for short breaks in the journey (up to 30 seconds) to account for events such as engine stalling where the reminder is not required to start again.

Euro NCAP also provides that for systems with rear seat occupant detection, the visual signal does not need to indicate the number of rear seat belts in use or not in use.

Section 3.4.1.

Section 3.4.2.1 (front); § 3.4.3.1.1 (rear).

Section 3.4.1.

Section 3.4.3.1.3.

For the rear seats, the IIHS protocol permits a 10-second delay between the ignition being turned on and the activation of the visual signal. Similar to ECE R16 and Euro NCAP, no visual signal is required for the rear seat belts if there are no unfastened belts at occupied seats.

The major differences between the proposal and other approaches were that, unlike ECE R16, we did not propose to refer to a “master control switch” because we did not believe it is necessary to introduce this new term into FMVSS No. 208; unlike Euro NCAP we proposed not allowing for short breaks in the journey; and unlike IIHS we did not propose allowing any delay after the ignition was turned on.

Comments

Commenters differed on whether the start-of-trip warning should be permitted to be delayed. HATCI and Ford supported the proposed trigger conditions (which did not permit a delay). On the other hand, Auto Innovators, NADA, Freedman, and Nissan recommended allowing a delay. Nissan, Auto Innovators, and NADA recommended aligning with the IIHS protocol and permitting a 10-second delay, while Freedman favored a 30-second delay. Auto Innovators also commented that while it generally supports the agency harmonizing with ECE R16, the agency should maintain flexibility for when these warnings are displayed on startup and allow for a brief delay for when the alert is provided. Freedman also commented that certain systems, such as an electronic system separate from that of the OEM system, will require a powerup and boot cycle which can take several seconds.

Auto Innovators also requested that the final rule allow the visual warning to be suppressed if all rear row seating positions are belted or determined to be empty based on occupant detection.

Lastly, RVIA explained that motor homes can be used in many ways other than for transportation, such that the ignition may be turned on with occupants seated in the rear accessing the vehicle's amenities, but with no intention of placing the vehicle in motion. RVIA was concerned that such use of the rear seats would trigger the rear seat belt visual warning, even though the motor homeowner has no intention of operating the vehicle. RVIA concluded that a visual warning system on vehicle start-up would often go unnoticed in this scenario, creating a requirement not suitable for the application of the start-up trigger in a motor home.

Agency Response

The final rule adopts the proposal for the warning to activate on start-up, with no provision for a delay. We continue to believe that basing the trigger on the ignition switch is preferable to delaying the warning until the vehicle is placed in gear because with a delay, there could be instances where a driver would pull out onto the road before the warning starts and before passengers have belted. The finalized requirements increase the likelihood that the occupants fasten their belts before the vehicle is in motion.

With respect to mitigating interaction with other vehicle warnings, NHTSA does not believe this will be an issue at vehicle start-up because critical safety warnings that activate at start-up would likely have dedicated space on the display. Interactions between warnings is discussed in more detail in Section VI.C.4. We believe consumers will accept this start-up warning. The longstanding current front seat belt warning is based on similar triggers and has not caused any issues. In addition, the rear start-of-trip warning is visual-only, so any potential annoyance is minimized. This factor distinguishes the rear-seat warning from the front seat belt warning, which we are requiring to be both audio-visual and to have two phases. We acknowledge there may be some scenarios during a trip where a rear seat belt warning is not required for an unbuckled occupant; for example, a passenger pickup scenario when the car is not turned off. In such a scenario, we are not requiring a warning because we are not requiring occupant detection, which would be necessary to detect the new occupant (and potentially avoid a false warning). Manufacturers of vehicles with rear-seat occupant detection may choose to provide warnings for such situations.

See

DOT 2009 Seat Belt Study at pg. 65.

In addition, we are modifying the proposed trigger condition related to the vehicle ignition being in the “on” or “start” position for both the front and rear seat belt warning to better account for EVs. This change is discussed in Section VI.C.1. This modification generally harmonizes with ECE R16, Euro NCAP, and the IIHS protocol, so that a vehicle that complies with the finalized trigger requirements can still meet these requirements; some exceptions are discussed immediately below.

In addition, we have also modified the proposal so that the final rule does not require a visual warning in three circumstances: (1) for an unoccupied seat if the system is able to determine whether a seat is occupied; (2) for a seat belt that is in use in a system designed to indicate to the driver how many or which rear seat belts are not in use; and (3) for a seat belt that is not in use in a system designed to indicate to the driver how many or which rear seat belts are in use. This regulatory text is intended to clarify two things.

First, that, depending on the type of seat belt reminder system and belt use/occupancy scenario, a visual signal may not be necessary for a particular DSP, or may not be necessary for any DSP. So, for example, no visual warning would be required for a negative-only system when every rear seat is occupied by a belted occupant. Another example: if no rear seats are occupied, no visual signal is required for negative-only, positive-only, or full-status systems with occupant detection; a visual warning would, however, be required in this case for a negative-only system without occupant detection (assuming that no rear belts were in use) and a full-status system without occupant detection.

This requirement is consistent with ECE R16, Euro NCAP, and IIHS.

Second, this also clarifies, in response to the comments, that systems utilizing symbols or numbers may utilize colors other than green or red to indicate unoccupied seats or seating positions for which the system is not providing information on belt use. Accordingly, a negative-only system would be permitted to display a pictogram that denotes a seating position with an in-use belt as grayed-out (to give one example).

See also

Section VI.C.3, Visual Warning Characteristics.

Freedman's comment regarding certain vehicles requiring more time to boot up appears to be referring to accommodating aftermarket systems. Because the final requirements apply to vehicles before first purchase other than for resale, they do not directly apply to aftermarket systems that are installed later on. However, § 30122 of the Safety Act prohibits a vehicle modifier from taking a vehicle out of compliance with an applicable FMVSS.

(The vehicle owner is not subject to the make inoperative provision). Therefore, a vehicle modification performed after the compliance date of this final rule on a vehicle with a rear seat belt warning system certified to the requirements in this rule that modifies the vehicle such that the rear seat belt visual warning does not activate when the ignition is in the “on” or “start” position (or upon manual activation of the propulsion system, but prior to the vehicle being placed in “possible active driving mode” as defined by FMVSS No. 305)

would violate § 30122 and would therefore not be permitted.

49 U.S.C. 30122(b) (“A manufacturer, distributor, dealer, rental company, or motor vehicle repair business may not knowingly make inoperative any part of a device or element of design installed on or in a motor vehicle or motor vehicle equipment in compliance with an applicable motor vehicle safety standard prescribed under this chapter unless the manufacturer, distributor, dealer, rental company, or repair business reasonably believes the vehicle or equipment will not be used (except for testing or a similar purpose during maintenance or repair) when the device or element is inoperative.”); section 30122(a) (“(a) Definition. In this section, “motor vehicle repair business” means a person holding itself out to the public to repair for compensation a motor vehicle or motor vehicle equipment.”).

See

Section VI.C.1.

The final rule does not incorporate RVIA's request to accommodate use scenarios specific to Recreational Vehicles (RVs). We agree that in the scenarios identified by RVIA the warning would activate when the vehicle was turned on with no intent to drive (thus obviating the need for a seat belt). A speed or motion trigger could address this issue, but we believe that such a trigger is undesirable because there is a safety benefit to having occupants belted before the vehicle is in motion or when it is travelling at lower speeds. Moreover, because the rear seat belt start-of-trip warning is visual-only, there are not the same consumer acceptance concerns that led us to include a speed criterion like we have included for the second-phase front seat belt audible warning. (See Section VI.B.3.) We could also potentially address this concern by either exempting RVs or crafting trigger criteria specific to RVs. We conclude the former is undesirable due to the significant safety benefit of belts when the vehicle is in motion, and that the latter would be overly complex. In addition, the rear seat belt start-of-trip warning is a mild visual warning that should not cause meaningful consumer annoyance (or condition them to ignore the warning) in these use cases.

iv. Seat Occupancy Criteria and Interaction With Child Restraint Systems

For rear seat belt warning systems that manufacturers voluntarily choose to equip with occupant detection, NHTSA proposed the occupancy criteria for the test dummy (or human, at the manufacturer's option) that NHTSA would position in the seat to conduct compliance testing of the system. NHTSA proposed that a rear designated seating position would be considered “occupied” when an occupant who weighs at least 46.5 lb (21 kg), and is at least 45 in (114 cm) tall, is seated there. These criteria are proxies for a 6-year-old child, which roughly corresponds to a typical age at which a child would begin using a seat belt (with a booster seat), transitioning from a forward-facing child restraint system (CRS). These are the same criteria used in FMVSS No. 208 to specify the smallest child that may be used as an alternative to the 6-year-old dummy in static suppression tests under FMVSS No. 208. We proposed using either a human being, at the manufacturer's option, or any anthropomorphic test device specified in 49 CFR part 572 that meets these proposed weight and height criteria (Section VI.C.8., Test Procedures).

The proposed criteria corresponded to a smaller occupant than ECE R16 or Euro NCAP, each of which essentially specifies an occupant (or load) no smaller than a 5th percentile adult female (

e.g.,

the HIII-5F specified in 49 CFR part 572). In the NPRM we explained that we believed that harmonizing with ECE R16 and using a heavier dummy would not capture the child segment of the population that could be restrained with a seat belt. We also did not believe it was necessary to use a larger-size occupant because a system capable of recognizing a 6-year-old should also be capable of recognizing larger occupants.

At the same time, we tentatively believed that the proposed criteria were preferable to criteria reflecting a younger occupant (lower weight). The smallest dummy that would meet the proposed weight and height criteria is the 6-year-old dummy specified in part 572. The next smallest dummy represents a 3-year-old child (

i.e.,

the Hybrid III 3-year-old); we believed it would not be appropriate to specify the use of the 3-year-old because a child represented by this dummy should be seated in a forward- or rear-facing CRS, not restrained with a seat belt.

NHTSA did not propose to require any sort of CRS detection capabilities. As explained in the NPRM, there are essentially three types of CRSs: rear-facing CRSs, forward-facing CRSs, and booster seats. Rear-facing and forward-facing CRSs are child seats that are installed using either Lower Anchors and Tethers for Children (LATCH) or a seat belt to secure it in place. Booster seats raise and position a child so the vehicle's lap-and-shoulder belt fits properly. We tentatively believed that a forward- or rear-facing CRS installed with the seat belt would not cause problematic false warnings; rather the system would just register the CRS as a buckled passenger. Similarly, we believed that a forward- or rear-facing CRS installed with LATCH would not pose issues necessitating any specific requirements related to the LATCH system, such as LATCH sensors.

We also did not believe a booster seat would present any special challenges to a seat belt warning system. If an unbelted child is in a booster seat, the system would register the belt as not fastened and, if equipped with occupant detection, that the seat was occupied. The system would not have to specifically detect the booster seat because the performance criteria are weight-based. In addition, we would not expect an occupant detection system to provide a false warning for an unoccupied booster seat because the proposed seat occupancy criterion (roughly equivalent to a 6-year-old) is heavier than an unoccupied booster seat. We did not propose to specify the use of a booster seat for testing because children may be prematurely transitioned to a seat belt without the use of a booster, and we believe it is desirable to test the lower end of the

possible weight range that encompasses children that could conceivably be restrained with a seat belt.

Comments

A number of commenters (Auto Innovators, Mercedes, GM, NADA, IEE, Honda, HATCI, and Consumer Reports) disagreed with the proposal and recommended harmonizing with ECE R16 and Euro NCAP and specifying occupancy criteria based on a 5th-percentile adult female occupant. These commenters made a variety of arguments.

Auto Innovators commented that harmonizing with the ECE requirements would avoid introducing unnecessary complexity and reduce the need for additional lead time to develop U.S.-specific designs. IEE commented that the proposed detection criterion would entail significant additional costs.

IEE also commented that a detection criterion based on the 5th percentile female would address the key target population of unbelted teenagers and adults. Relatedly, IEE noted that the NPRM analysis investigated potential benefits for the age group 6 to 10 years old and only found a very small belt usage increase (by only 0.27 percent to 0.41 percent) and concluded that members of this age group already have high rates of seat belt use (98 percent according to the preliminary regulatory impact analysis).

Consumer Reports, IEE, Auto Innovators, Honda, HATCI, NADA, RVIA, and GM raised concerns regarding feasibility. Consumer Reports agreed with NHTSA on the importance of testing the lower end of the possible weight range that encompasses children that could conceivably be restrained with a seat belt alone, but believed that it would be premature to require the detection of dummies smaller than the 5th percentile adult female because the ability to detect occupants smaller than the 5th percentile adult female is limited. IEE commented that while detecting a 5th percentile female is well-established in the market and would not present any design or technical challenges, it was not aware of any car on the market that would be able to meet the proposed detection of the 6-year-old child scenarios, with or without a booster cushion. IEE commented that the 5th percentile female is the state-of-the art in contemporary sensing technology for seat belt reminder-related occupant detection and that no realistic alternative technologies are readily available at comparably low costs. IEE stated that it believed that the 7 percent of U.S. MY 2022 vehicles with rear seat occupant detection all meet the 5th percentile female detection criterion, not the one 6-year-old proposed in the NPRM.

IEE also commented that the proposal assumed that a 6-year-old child on the booster seat would be automatically covered and detected as it has a higher total weight than the weight proposed for the occupancy criteria. IEE stated that this assumption is wrong: rear occupant detection systems are designed to detect a load that is generating a pressure profile on the seat foam that matches the pressure profile of a human buttocks. IEE commented that the pressure profile generated by a booster seat is different and would not be classified by the system as an occupant; contemporary occupant detection sensors used for seat belt reminder systems are not designed to detect booster seats, and child seats are considered as non-detection objects. IEE indicated that this distinction is also required to differentiate between humans and objects, to avoid objects that would be likely to trigger false positives. Auto Innovators similarly commented that the contact area between a booster seat and a seat cushion can vary, causing some of the occupant's weight to be distributed to the seat itself or to the LATCH system, rather than to the weight sensor.

Auto Innovators also pointed out that child occupants are also more likely to be out-of-position compared to an adult, further contributing to uneven weight transfer. Auto Innovators argued that if the weight of a child in a booster seat is not transferred to the weight sensor, the proposed system could misclassify the seat as empty. If this misclassification occurs, coupled with the lack of a visual warning for an unfastened seat belt at an unoccupied seat, Auto Innovators argued there would be no visual warning for cases where an age-appropriate child is sitting in a booster seat and not wearing a belt. Relatedly, IEE commented that more advanced detection technologies (such as cameras or radar sensors) are not currently used in the context of a seat belt reminder function, and that these technologies would still have to prove their reliability and robustness for the occupant detection needs of a seat belt reminder system. IEE explained that while future developments may enable the support of seat belt reminder functionalities with these technologies, it is too early to consider such a potential innovation in a regulatory pass/fail scenario.

Honda, HATCI, Auto Innovators, NADA, IEE, RVIA, Honda, and GM commented that specifying criteria matching a 6-year-old would exacerbate the problem of false positives. HATCI and IEE commented that behavioral alternatives to avoid false positives, such as moving cargo to the floor of the vehicle or buckling the belt before loading heavy cargo onto seats, may not always be feasible or reliable. Auto Innovators and Honda argued that the proposed criteria would potentially discourage manufacturers from implementing occupant detection systems due to the potential for false warnings.

IEE similarly commented that if the agency were to adopt the 6-year-old criterion proposed in the NPRM, manufacturers would be disincentivized from implementing occupant detection in rear seats. IEE explained that because the proposed detection threshold is not technically feasible today within a regulatory pass/fail context, the threshold proposed in the NPRM would fail advanced rear seat belt reminder systems that have already entered the U.S. market and that offer a seat belt warning functionality that exceeds the proposed legal minimum. IEE stated that this requirement would force vehicle manufacturers to withdraw these advanced seat belt reminder systems from the market and downgrade the seat belt reminder systems features to the legal minimum (the positive-only compliance option). IEE argued that this result would be counterproductive from a safety perspective.

IEE and Consumer Reports commented that manufacturers could voluntarily detect occupants smaller than the 5th percentile female. IEE argued that making such detection voluntary would provide flexibility for innovation. Consumer Reports recommended that NHTSA incorporate detection of dummies smaller than the 5th percentile female into NCAP ratings for rear seat belt reminders, which would award manufacturers for going above and beyond the regulatory minimum and drive innovation.

On the other hand, NSC and SRN suggested a 3-year-old child for the occupancy criterion. NSC commented that data from the National Digital Car Seat Check Form show that many children are not riding in the appropriate CRS based on their height and weight, so specifying criteria corresponding to a 3-year-old child would protect children. SRN similarly noted that the weight of a 3-year-old dummy, though average for a toddler, is also the weight of many older children in the lower growth chart percentiles. SRN argued that since nearly all school-age children ride in seat belts or boosters (including these lighter-weight

children, regardless of NHTSA best-practice recommendations), families would benefit from warnings about the belt-use status of those children. SRN explained that this is especially true for warnings that a passenger has unbuckled during a ride, which younger, less mature children may be prone to do. SRN explained that, as proposed, a system with occupant detection would not recognize some of the youngest booster/belt users, may provide inadequate warnings to families, and may cause caregivers some frustration in interpreting status indicators. SRN also commented that in comments to the ANPRM, SRN had voiced the concern that LATCH-installed car seats could trigger false alarms. SRN was less concerned that the proposed system will rise to the level of nuisance and is more concerned that false warnings will happen, such as when relatively heavy car seats are installed using LATCH. SRN argued that owners will need clear guidance in owner's manuals on how to interpret warnings when traveling with children, and that these instructions should be included (or at least referenced) in the child passenger section of the manual.

Consumer Reports, HATCI, and Freedman agreed with NHTSA that a CRS detection requirement was not necessary. Consumer Reports stated that consumers might be better served by incorporating CRS detection into a component of NCAP for rear seat belt reminder systems to help drive safety innovation. Freedman commented that the easiest and most effective solution for LATCH-installed CRS is to continue recommending the seat belt be fastened behind the CRS.

Auto Innovators and GM recommended that NHTSA ensure a technology-neutral approach that includes consideration of compliance options that permit the use of camera- or vision-based sensors, or other technologies that may be adopted in lieu of weight-based sensors, as a means for determining occupant presence at a given designated seating position. Advocates and Public Citizen commented that the final rule should not preclude or discourage the use of existing state-of-the-art technology.

Agency Response

After considering the comments, NHTSA has decided to adopt the proposal to use (at the option of the manufacturer) either a anthropomorphic test device at least as large as a 49 CFR part 572, subpart N 6-year-old child dummy or a person, at the manufacturer's option, that is at least 21 kg in weight and 114 cm in height to define an occupied rear designated seating position for the purposes of testing the rear seat belt reminder system. These criteria represent a 50th percentile 6-year-old child, and only specify the low end of the occupancy criteria used for compliance testing. Therefore, when we refer to a 6-year-old as our occupancy criteria, this includes occupants or dummies that are larger.

Before addressing the specific issues raised by the commenters, it is important to recognize that this final rule does not require or necessitate occupant detection. Moreover, we recognize that a manufacturer currently deploying reminder systems with occupant detection based on the 5th percentile female would likely need some time and effort to develop and implement new sensor solutions in the rear. Based on MY 2022 NCAP data, approximately 7 percent of vehicles sold in the U.S. are equipped with rear seat belt reminders using occupant detection. The commenters, however, did not provide specific information on what additional development would be necessary to meet the requirements when tested with a 6-year-old.

Further, as explained above (Section VI.A.2.a.i) we have revised the proposed requirements to provide greater flexibility for systems without occupant detection. The proposal only included one compliance option (the positive-only compliance option) without occupant detection. In response to the comments, the final rule would allow for additional warning systems without occupant detection (

e.g.,

negative-only and full-status). Given this flexibility, manufacturers can simply use reminder systems without occupant detection if they believe they cannot deploy a reminder system using occupant detection that would comply with the requirements when tested with a 6-year-old.

Given the above, NHTSA has concluded that it would fulfill the MAP-21 mandate, meet the need for safety, and be practicable and appropriate to require that an occupant detection system be capable of detecting at least a 6-year-old. There are several reasons for this decision.

First, section 31503 of MAP-21 directs NHTSA to initiate (and finalize, if the § 30111 criteria are met) a rulemaking proceeding “to provide a safety belt use warning system for designated seating positions in the rear seat.” Section 31503 itself does not refer to particular classes of occupants or identify a target population. “Subtitle E—Child Safety Standards”, in which § 31503 is located, however, contains four mandates related to child passenger safety: improving the protection seated in CRSs during side impact crashes; improving the ease of use for LATCH systems; providing seat belt reminders for rear seats; and researching the risk of hyper- or hypothermia to children or other unattended passengers in rear seating positions.

93 94

See, e.g.,

Norman J. Singer & Shambie Singer, 2b Sutherland Statutory Construction section 46:5 (7th ed.) (“[E]ach part or section of a statute should be construed in connection with every other part or section to produce a harmonious whole. Thus, it is not proper to confine interpretation to the one section to be construed.”); section 47:3 (explaining that while legislative titles cannot control a statute's plain words they “may help resolve uncertainty” and “illuminat[e] statutory meaning”). See also

id.

section 47:6 (“Courts give effect to all the language of a purview as a harmonious whole, in light of the statute's purpose, and regardless of sectional formatting, unless to do so is plainly contrary to legislative intent.”).

MAP-21, Division C, Title I, “MOTOR VEHICLE AND HIGHWAY SAFETY IMPROVEMENT ACT OF 2012.”

In addition, the Safety Act gives NHTSA the discretionary authority to issue safety standards to address specific safety needs, provided that the standard is objective, practicable, and appropriate for the type(s) of vehicles to which it applies.

NHTSA has concluded that requiring a rear seat belt warning system equipped with occupant detection be able to detect unbelted children smaller than the size represented by the 5th percentile female crash test dummy meets a safety need and is practicable and appropriate.

49 U.S.C. 30111.

Specifying occupant characteristics corresponding to a 5th percentile female would not address rear seat belt usage by children because the vast majority of children are smaller than the 5th percentile female test dummy. The population of children seated in the rear who should be restrained with a seat belt is comprised of children seated in a booster seat and children who have transitioned out of a booster seat to sit directly on the vehicle seat. As we explained in the NPRM, children typically begin sitting in a booster seat (transitioning out of a forward-facing CRS) around 4-7 years old (depending on the height and weight of the child and the respective limits of their forward-facing car seat). Children typically transition out of a booster seat between the ages of about eight and thirteen (again, exactly when depends on the child's height and weight). The Hybrid III 5th percentile female crash test dummy weighs 108 lb (50 kg). This weight corresponds (approximately) to a 50th percentile fourteen-year-old girl and a 50th percentile thirteen-and-a-half-year-old boy.

This means that if

NHTSA were to specify criteria matching the 5th percentile female, it would essentially be ignoring a large percentage of children ages 6-14, and likely some 15-18 year old children with weight lower than that of a 5th percentile female. That is, if NHTSA specified the 5th percentile female, the rear seat belt warning requirements would only be targeting older children, not younger children.

This disparity strongly suggests that NHTSA should specify a smaller occupant for testing if doing so would be practicable.

Center for Disease Control Growth Charts for Children 2-20 years of age: Boys Stature-for-age and

Weight-for-age percentiles and Girls Stature-for-age and Weight-for-age percentiles, published in May 2000 (modified in November 2000) and

available at https://www.cdc.gov/growthcharts/data/set1clinical/cj41c022.pdf

and

https://www.cdc.gov/growthcharts/data/set1clinical/cj41c021.pdf,

respectively. (last accessed September 10, 2024).

A booster seat augments the total weight on the rear seat. However, as we explained in the NPRM—and as we adopt in this final rule—we will not be testing with a booster seat because we are aware that children can be prematurely transitioned to a seat belt without the use of a booster, and we believe it is desirable to test the lower end of the possible weight range that encompasses children that could conceivably be restrained with a seat belt alone. We discuss the issue of booster seats in our discussion regarding feasibility later in this section.

Although NHTSA has concluded that specifying occupant characteristics matching those of a 6-year-old child would meet a safety need and be fully consistent with MAP-21, MAP-21 directs NHTSA to issue a final rule only if the rule would meet the criteria set out in § 30111 of the Safety Act. These criteria include that the rule be practicable. As noted earlier, the statutory criterion of practicability is multidimensional (see Section IV. Statutory Authority). After considering the comments, NHTSA agrees that most currently deployed rear seat belt warning systems utilizing occupant detection are not able (or designed) to reliably detect a 6-year-old occupant. NHTSA also agrees with the commenters who indicated that there are a number of challenges to rear-seat occupant detection, related both to false negatives and false positives. However, while many or most currently deployed rear occupant detection systems used for seat belt warnings may not comply with the requirements in the final rule, we believe that OEMs are capable of improving the technology and meeting these challenges. Further, NHTSA believes that selecting a 6-year-old child instead of the 5th percentile female appropriately balances benefits and costs. We explain this conclusion in more detail below.

NHTSA believes that while current occupant detection systems might not reliably detect a 6-year-old child, or a booster seat, such a requirement is feasible. NHTSA acknowledges the commenters who argued that many or most rear occupant detection systems that are currently deployed may not be able to reliably detect a 6-year-old occupant, either seated directly on the seat or in a booster seat. NHTSA has not tested current systems to verify or refute this claim, so we have no firm basis on which to agree or disagree with these comments. NHTSA has, though, noted that some owner's manuals inform consumers that if they place lightweight objects (such as a briefcase) on the rear seat, it may trigger the seat belt warning; this suggests that some rear seat belt occupant detection systems may be capable of detecting younger (and therefore lighter) occupants. For example, the owner's manual for the MY 2024 Cadillac Escalade states that “[t]he rear passenger seat belt reminder light and chime may come on if an object is put on the seat such as a briefcase, handbag, grocery bag, laptop, or other electronic device. To turn off the reminder light and/or chime, remove the object from the seat or buckle the seat belt.”

In most cases the weights of these listed items would be less than the weight of a 6-year-old. Furthermore, we understand (although again, have not been able to verify) that at least one manufacturer's system may be able to detect a 6-year-old not in a booster.

Page 114. As another example, the owner's manual for the MY 2024 Tesla Model Y states: “If all occupants are buckled up and the [seat belt] reminder stays on, . . . remove any heavy objects (such as a briefcase) from an unoccupied seat.”

NHTSA is not disclosing further details about this finding because this information is confidential.

We also acknowledge that some rear-seat occupant detection systems may not be able to reliably classify a young child seated in a booster seat as an occupant. We explained in the NPRM that children start using belts (with a booster seat) at about 6 years old, and typically transition out of a booster seat around 8 to 13 years old. We acknowledge, as IEE commented, that some rear detection systems may not simply classify objects/occupants based on weight, but may also base the classification on other information, such as the pressure profile, so that a child seated in a booster seat may not be classified as a human occupant, regardless of the child's weight and height. We recognize that manufacturers would have to develop a solution to this issue. We also acknowledge other issues pointed out by the commenters that make accurate detection a challenge, such as out-of-position children.

Nevertheless, we believe that it is feasible to develop this technology. We agree with IEE that more advanced technologies (such as radar sensors) are not yet proven. However, occupant detection technology similar to that used for advanced air bag testing in the front that is used to detect different sized dummies in different test scenarios,

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including 6-year-old dummies, could potentially be reprogrammed to address our occupancy criteria needs and this would also address the comments about not being able to detect children in boosters. Testing with a 6-year-old should also be compatible with the requirements in ECE R16 and Euro NCAP; if a system can recognize a 6-year-old occupant, it should also be able to recognize an occupant with the characteristics of the 5th percentile female. Moreover, to give manufacturers flexibility, we have kept the requirements as technology-neutral as possible in order to facilitate innovation. We acknowledge that requiring an occupant detection system to meet the final requirements when tested with a dummy or human representing a 6-year-old could increase the cost of the system and may take some time to implement and test, but again, the final rule does not require occupant detection. We are also providing two years of lead time, so current occupant detection systems could be offered until then (See Section IX, Compliance Date).

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The Advanced Air Bag rule was targeted at protecting all individuals from potential harm from air bags; specific requirements were included that were targeted at protecting children.

See

Section VI.A.2.a.1.

With respect to the comments on cargo (or pets) leading to false warnings based on the relatively low weight specification for the occupancy criteria, while this is a potential issue, we believe that it is mitigated in a variety of ways. First, potential consumer annoyance should be mitigated by the relatively short duration of the warning (60 sec) and the fact that it does not have an audible component. The weight of the types of objects typically placed on the rear seats (such as briefcases, water bottles, and groceries) would also likely be well under the weight of a 6-year-old (46.5 lb).

There may also be technical solutions to mitigate false warnings. Several comments referred to complications with detection related to the weight of the occupant or object placed on the seat. However, occupant detection technology reliant solely on weight-based sensors may not necessarily be the only technology solution to meet the performance requirements in this final

rule. We also note that, based on the comments alone, it appears that there are presently issues with false alarms for current systems which are presumably based on detecting a 5th percentile female occupant. (However, no specific data were provided on the performance of these systems with relation to false warnings or how such false warnings have affected acceptance.)

If technical solutions to mitigating any remaining consumer acceptance concerns are not readily available, NHTSA continues to believe the behavioral solutions we suggested in the NPRM (such as placing objects on the floor instead of the seat, or buckling the belt if cargo is placed on the seat) are viable. Although Honda and HATCI did not believe such behavioral solutions were viable, as noted earlier, at least some manufacturers are already providing such guidance in the owner's manual. We acknowledge that there may be some trade-off in effectiveness if consumers frequently buckle the belt when cargo is placed on the seat or become accustomed to ignoring the warning. (We are not aware of any data or research on such trade-offs.) Nevertheless, we believe that this concern would not meaningfully affect the warning's effectiveness, and that any lessening in effectiveness should be offset by the system being able to detect the full range of occupants that should be using a seat belt.

With respect to interactions between the occupant detection system and CRSs, we agree with the commenters that the final rule should not require that the occupant detection system be able to detect a forward- or rear-facing CRS installed with LATCH. We agree with Freedman and Honda that the easiest and most effective solution to avoid false warnings for LATCH-installed CRSs is to continue recommending the seat belt be fastened behind the CRS. We encourage this practice on our website

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and some manufacturers are already providing consumers with this guidance.

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See

www.nhtsa.gov/road-safety/child-safety

(last accessed May 16, 2024).

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For example, the owner's manual for the MY 2024 Subaru Forester advises the consumer that “[t]he seatbelt warning system of the rear seats detects if any of the seats are occupied by a passenger. Installing a child restraint system in the rear seating area, using the LATCH anchors, may result in the activation of the passenger seatbelt warning light and chime. Fastening the rear seatbelt prior to installing the child restraint system will avoid activating the passenger seatbelt warning light and chime.”

NHTSA also considered the relative costs and benefits of specifying a 6-year-old child as opposed to the 5th percentile female. In particular, we considered some commenters' assertions that specifying the 6-year-old would discourage manufacturers from adopting systems with occupant detection or would force manufacturers to downgrade their systems to the positive-only option (which did not require occupant detection). We have concluded that specifying a 6-year-old as opposed to the 5th percentile female appropriately balances costs and benefits. There are several reasons for this conclusion.

First, and most important, a system that does not monitor child occupants smaller than a 5th percentile female does not monitor the entire population of children who can and should be using seat belts. As we noted above, the height and weight of the 5th percentile female dummy correspond, approximately, to that of a 14-year-old. Because the 5th percentile female dummy would not represent most younger children, the system would not work accurately for these children. This is especially worrisome given that children 12 years old and younger represent more than half of the rear seat occupant population.

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See https://www.nhtsa.gov/crashworthiness/child-safety-crashworthiness-research#:~:text=Since%20children%2012%2Dyears%2Dold,booster%20seats%20and%20seat%20belts

(last accessed May 16, 2024).

Accordingly, specifying the 5th percentile female could result in unbelted child occupants in the rear not benefiting from the seat belt warning. For instance, if a negative-only system with occupant detection did not detect an unbelted child smaller than the 5th percentile female seated in a rear seat, the visual warning would not indicate an unbelted occupant at an occupied seat (

e.g.,

for systems with a pictogram that indicates which seat are not in use, the pictogram would likely display something like a “grayed-out” seat to indicate that the system was registering a seat as unoccupied)

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