FMVSS 209: Seat belt assemblies explained.

What FMVSS 209 says it is for

The eCFR heads this section "Standard No. 209; Seat belt assemblies." Under 49 CFR part 571, the Federal Motor Vehicle Safety Standards are the numbered standards that set safety performance requirements for motor vehicles and equipment. The text below is quoted from 571.209 as current through October 29, 2026.

This standard specifies requirements for seat belt assemblies.

What it applies to

The application section of the standard says:

This standard applies to seat belt assemblies for use in passenger cars, multipurpose passenger vehicles, trucks, and buses.

Applicability is decided by the text of the standard as written, including any exclusions it lists, and by the date-specific rules in it. This page does not decide whether a particular vehicle or item is covered.

How the standard is organized

The eCFR text of 571.209 has these top-level sections:

• S1: Purpose and scope
• S2: Application
• S3: Definitions
• S4: Requirements
• S5: Demonstration procedures

In all, the text has 14 numbered headings. Use the finder above to search them; for example, a search for "test" lists the headings that mention tests.

Key requirements, quoted from the text

These are excerpts from the requirements sections of 571.209, in the order the standard presents them. Long paragraphs are shortened where marked; the eCFR has the complete text, tables and figures, which this page omits.

S4.2 Requirements for webbing. (a) Width. The width of the webbing in a seat belt assembly shall be not less than 46 mm, except for portions that do not touch a 95th percentile adult male with the seat in any adjustment position and the seat back in the manufacturer's nominal design riding position when measured under the conditions prescribed in S5.1(a). (b) Breaking strength. The webbing in a seat belt assembly shall have not less than the following breaking strength when tested by the procedures specified in S5.1(b): Type 1 seat belt assembly—26,689 N; Type 2 seat belt assembly—22,241 N for webbing in pelvic restraint and 17,793 N for webbing in upper torso restraint. (c) Elongation. [excerpt continues in the eCFR]

S4.3 Requirements for hardware. (a) Corrosion resistance. (1) Attachment hardware of a seat belt assembly after being subjected to the conditions specified in S5.2(a) shall be free of ferrous corrosion on significant surfaces except for permissible ferrous corrosion at peripheral edges or edges of holes on underfloor reinforcing plates and washers. Alternatively, such hardware at or near the floor shall be protected against corrosion by at least an electrodeposited coating of nickel, or copper and nickel with at least a service condition number of SC2, and other attachment hardware shall be protected by an electrodeposited coating of nickel, or copper and nickel with a service condition number of SC1, in accordance with ASTM B456-79 (incorporated by reference, see § 571.5), but such hardware shall not be racked for electroplating in [excerpt continues in the eCFR]

S4.4 Requirements for assembly performance. (a) Type I seat belt assembly. Except as provided in S4.5, the complete seat belt assembly including webbing, straps, buckles, adjustment and attachment hardware, and retractors shall comply with the following requirements when tested by the procedures specified in S5.3(a): (1) The assembly loop shall withstand a force of not less than 22,241 N; that is, each structural component of the assembly shall withstand a force of not less than 11,120 N. (2) The assembly loop shall extend not more than 7 inches or 178 mm when subjected to a force of 22,241 N; that is, the length of the assembly between anchorages shall not increase more than 356 mm. [excerpt continues in the eCFR]

S4.5 Load-limiter. (a) A Type 1 or Type 2 seat belt assembly that includes a load-limiter is not required to comply with the elongation requirements of S4.2(c), S4.4(a)(2), S4.4(b)(4) or S4.4(b)(5). (b) A seat belt assembly that includes a load limiter and that does not comply with the elongation requirements of this standard may be installed in motor vehicles at any designated seating position that is subject to the requirements of S5.1 of Standard No. 208 (§ 571.208).

S4.6 Manual belts subject to crash protection requirements of Standard No. 208. (a)(1) A manual seat belt assembly, which is subject to the requirements of S5.1 of Standard No. 208 (49 CFR 571.208) by virtue of any provision of Standard No. 208 other than S4.1.2.1(c)(2) of that standard, does not have to meet the requirements of S4.2(a)-(f) and S4.4 of this standard. (2) A manual seat belt assembly subject to the requirements of S5.1 of Standard No. 208 (49 CFR 571.208) by virtue of S4.1.2.1(c)(2) of Standard No. 208 does not have to meet the elongation requirements of S4.2(c), S4.4(a)(2), S4.4(b)(4), and S4.4(b)(5) of this standard.

S5.1 Webbing. —(a) Width. The width of webbing from three seat belt assemblies shall be measured after conditioning for at least 24 hours in an atmosphere having relative humidity between 48 and 67 percent and a temperature of 23° ±2 °C. The tension during measurement of width shall be not more than 22 N on webbing from a Type 1 seat belt assembly, and 9786 N ±450 N on webbing from a Type 2 seat belt assembly. The width of webbing from a Type 2 seat belt assembly may be measured during the breaking strength test described in paragraph (b) of this section. (b) Breaking strength. [excerpt continues in the eCFR]

S5.2 Hardware. (a) Corrosion resistance. Three seat belt assemblies shall be tested in accordance with ASTM B117-73 (Reapproved 1979) (incorporated by reference, see § 571.5). Any surface coating or material not intended for permanent retention on the metal parts during service life shall be removed prior to preparation of the test specimens for testing. The period of test shall be 50 hours for all attachment hardware at or near the floor, consisting of two periods of 24 hours exposure to salt spray followed by 1 hour drying and 25 hours for all other hardware, consisting of one period of 24 hours exposure to salt spray followed by 1 hour drying. [excerpt continues in the eCFR]

S5.3 Assembly performance—(a) Type 1 seat belt assembly. Three complete seat belt assemblies, including webbing, straps, buckles, adjustment and attachment hardware, and retractors, arranged in the form of a loop as shown in Figure 5, shall be tested in the following manner: (1) The testing machine shall conform to the requirements specified in S5.1(b). A double-roller block shall be attached to one head of the testing machine. This block shall consist of two rollers 102 mm in diameter and sufficiently long so that no part of the seat belt assembly touches parts of the block other than the rollers during test. [excerpt continues in the eCFR]

S5.4 Tolerances on angles. Unless a range of angles is specified or a tolerance is otherwise explicitly provided, all angles and orientations of seat belt assemblies and components specified in this standard shall have a tolerance of ±3 degrees.

Defined terms

The standard defines 18 terms in its definitions section. Definitions are quoted from the eCFR.

• Adjustment hardware means any or all hardware designed for adjusting the size of a seat belt assembly to fit the user, including such hardware that may be integral with a buckle, attachment hardware, or retractor.
• Attachment hardware means any or all hardware designed for securing the webbing of a seat belt assembly to a motor vehicle.
• Automatic-locking retractor means a retractor incorporating adjustment hardware by means of a positive self-locking mechanism which is capable when locked of withstanding restraint forces.
• Buckle means a quick release connector which fastens a person in a seat belt assembly.
• Emergency-locking retractor means a retractor incorporating adjustment hardware by means of a locking mechanism that is activated by vehicle acceleration, webbing movement relative to the vehicle, or other automatic action during an emergency and is capable when locked of withstanding restraint forces.
• Hardware means any metal or rigid plastic part of a seat belt assembly.
• Load-limiter means a seat belt assembly component or feature that controls tension on the seat belt to modulate the forces that are imparted to occupants restrained by the belt assembly during a crash.
• Nonlocking retractor means a retractor from which the webbing is extended to essentially its full length by a small external force, which provides no adjustment for assembly length, and which may or may not be capable of sustaining restraint forces at maximum webbing extension.
• Pelvic restraint means a seat belt assembly or portion thereof intended to restrain movement of the pelvis.
• Retractor means a device for storing part or all of the webbing in a seat belt assembly.
• Seat back retainer means the portion of some seat belt assemblies designed to restrict forward movement of a seat back.
• Seat belt assembly means any strap, webbing, or similar device designed to secure a person in a motor vehicle in order to mitigate the results of any accident, including all necessary buckles and other fasteners, and all hardware designed for installing such seat belt assembly in a motor vehicle.
• Strap means a narrow nonwoven material used in a seat belt assembly in place of webbing.
• Type 1 seat belt assembly is a lap belt for pelvic restraint.
• Type 2 seat belt assembly is a combination of pelvic and upper torso restraints.
• Type 2a shoulder belt is an upper torso restraint for use only in conjunction with a lap belt as a Type 2 seat belt assembly.
• Upper torso restraint means a portion of a seat belt assembly intended to restrain movement of the chest and shoulder regions.
• Webbing means a narrow fabric woven with continuous filling yarns and finished selvages.

Limits of this page

This page quotes the text of 49 CFR 571.209 as published in the eCFR, current through October 29, 2026. It omits tables, figures, cross-referenced test procedures in other parts, and the preambles and rulemaking history that explain the rule. It does not tell you whether a given vehicle, part or product complies, how to run a test, or what a manufacturer must certify. Compliance questions go to the manufacturer's engineers, qualified counsel or NHTSA. The eCFR is an editorial compilation, not the official legal edition of the Federal Register.

Sources

Sources opened and read November 2, 2026.

• eCFR: 49 CFR 571.209, Standard No. 209; Seat belt assemblies. (current through October 29, 2026) (read November 2, 2026)
• eCFR: 49 CFR part 571, Federal Motor Vehicle Safety Standards (current through October 29, 2026) (read November 2, 2026)