FMVSS 223: Rear Impact Guards explained.

What FMVSS 223 says it is for

The eCFR heads this section "Standard No. 223; Rear impact guards." 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 571.223 as current through October 29, 2026.

This standard specifies requirements for rear impact guards for trailers and semitrailers.

The purpose of this standard is to reduce the number of deaths and serious injuries that occur when light duty vehicles collide with the rear end of trailers and semitrailers.

What it applies to

The application section of the standard says:

This standard applies to rear impact guards for trailers and semitrailers subject to Federal Motor Vehicle Safety Standard No. 224, Rear Impact Protection (§ 571.224).

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 571.223 has these top-level sections:

• S1: Scope
• S2: Purpose
• S3: Application
• S4: Definitions
• S5: Requirements
• S6: Guard Test Procedures

In all, the text has 22 numbered headings. Use the finder above to search them; for example, a search for "test" lists the headings that mention tests.

Second-level headings at a glance

These are the numbered sub-sections one level below the top, in order (first 12 of 14):

• S5.1 Projected Vertical Height
• S5.2 Strength and Energy Absorption
• S5.3 Labeling
• S5.4 Guard Attachment Hardware
• S5.5 Installation Instructions
• S6.1 Preparation of Hydraulic Guards
• S6.2 Guard Installation for Strength and Energy Absorption Tests
• S6.3 Point Load Force Application Device
• S6.4 Point Load Test Locations
• S6.5 Positioning of Force Application Device
• S6.6 Force Application
• S6.7 Uniform Distributed Load Force Application Device

Key requirements, quoted from the text

These are excerpts from the requirements sections of 571.223, in the order the standard presents them. Long paragraphs are shortened where marked with [...]; the eCFR has the complete text, tables and figures, which this page omits.

S5.1 Projected Vertical Height. The horizontal member of each guard, when viewed from the rear as it would be installed on a trailer pursuant to the installation instructions or procedures required by S5.5 of this standard, shall have a vertical height of at least 100 mm at each point across the guard width, when projected horizontally on a transverse vertical plane. Those installation instructions or procedures shall specify that the guard is to be mounted so that all portions of the horizontal member necessary to achieve a 100 mm high projected vertical height are located not more than 305 mm forward of the vehicle's rear extremity, as defined in S4 of 49 CFR 571.224, Rear Impact Protection. See Figure 1 of this section.

S5.2 Strength and Energy Absorption. When tested under the procedures of S6 of this section, each guard shall comply with the strength requirements of S5.2.1 of this section at each test location and the energy absorption requirements of S5.2.2 of this section when a distributed load is applied uniformly across the horizontal member, as specified in S6.8 of this section. However, a particular guard (i.e., test specimen) need not be tested at more than one location.

S5.2.1 Guard Strength. The guard must resist the force levels specified in S5.2.1(a) through (c) of this section without deflecting by more than 125 mm and without eliminating any load path that existed before the test was initiated. (a) A force of 50,000 N applied in accordance with S6.6 of this section at test location P1 on either the left or the right side of the guard as defined in S6.4(a) of this section. (b) A force of 50,000 N applied in accordance with S6.6 of this section at test location P2 as defined in S6.4(b) of this section. (c) A uniform distributed force of at least 350,000 N applied across the horizontal member, as specified in S6.8 of this section and in accordance with S6.6 of this section.

Defined terms

The standard defines 8 terms in its definitions section; the first 8 are quoted here from the eCFR.

• Chassis means the load supporting frame structure of a motor vehicle.
• Guard width means the maximum horizontal guard dimension that is perpendicular to the longitudinal vertical plane passing through the longitudinal centerline of the vehicle when the guard is installed on the vehicle according to the installation instructions in S5.5 of this section.
• Ground clearance means the vertical distance from the bottom edge of a horizontal member to the ground.
• Horizontal member means the structural member of the guard that meets the configuration requirements of S5.1.1 through 5.1.3 of § 571.224, Rear Impact Protection, when the guard is installed on a vehicle according to the guard manufacturer's installation instructions.
• Hydraulic guard means a guard designed to use fluid properties to provide resistance force to deformation.
• Load path means a route of force transmission between the horizontal member and the chassis.
• Rear impact guard means a device installed on or near the rear of a vehicle so that when the vehicle is struck from the rear, the device limits the distance that the striking vehicle's front end slides under the rear end of the impacted vehicle.
• Rigid test fixture means a supporting structure on which a rear impact guard can be mounted in the same manner it is mounted to a vehicle. The rigid test fixture is designed to resist the forces applied to the rear impact guard without significant deformation, such that a performance requirement of this standard must [...]

Limits of this page

This page quotes the text of 49 CFR 571.223 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 571.223, Standard No. 223; Rear impact guards. (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)