FMVSS 125: Warning Devices explained.

What FMVSS 125 says it is for

The eCFR heads this section "Standard No. 125; Warning devices." 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 571.125 as current through October 29, 2026.

This standard establishes requirements for devices, without self-contained energy sources, that are designed to be carried in motor vehicles and used to warn approaching traffic of the presence of a stopped vehicle, except for devices designed to be permanently affixed to the vehicle.

The purpose of this standard is to reduce deaths and injuries due to rear end collisions between moving traffic and disabled vehicles.

What it applies to

The application section of the standard says:

This standard applies to devices, without self-contained energy sources, that are designed to be carried in buses and trucks that have a gross vehicle weight rating (GVWR) greater than 10,000 pounds. These devices are used to warn approaching traffic of the presence of a stopped vehicle, except for devices designed to be permanently affixed to the vehicle.

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 571.125 has these top-level sections:

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

In all, the text has 30 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 10 of 10):

• S5.1 Equipment
• S5.2 Configuration
• S5.3 Color
• S5.4 Reflectivity
• S5.5 Luminance
• S5.6 Stability
• S5.7 Durability
• S6.1 Conditions
• S6.2 Reflectivity Test
• S6.3 Luminance Test

Key requirements, quoted from the text

These are excerpts from the requirements sections of 571.125, 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.

S5.1.1. Reflex reflective material and fluorescent material that meet the requirements of this standard shall be affixed to both faces of the warning device. Alternatively, a dual purpose orange fluorescent and red reflective material that meets the requirements of this standard (hereafter referred to as “dual purpose material”) may be affixed to both faces in places of the reflective and fluorescent materials.

S5.1.2 Each warning device shall be protected from damage and deterioration. (a) By enclosure in an opaque protective reusable container, except that two or three warning devices intended to be sold for use as a set with a single vehicle may be enclosed in a single container; or (b) By secure attachment to any light-tight, enclosed, and easily accessible compartment of a new motor vehicle with which it is supplied by the vehicle manufacturer.

S5.1.4 The warning device shall be permanently and legibly marked with. (a) Name of manufacturer; (b) Month and year of manufacture, which may be expressed numerically, as “6/72”; and (c) The symbol DOT, or the statement that the warning device complies with all applicable Federal motor vehicle safety standards.

Defined terms

The standard defines 4 terms in its definitions section; the first 4 are quoted here from the eCFR.

• Entrance angle means the angle having as its sides the line through the center, and normal to the face, of the object to be tested, and the line from the center of the object to the center of the source of illumination (Figure 2).
• Fluorescent means the property of emitting visible light due to the absorption of radiation of a shorter wavelength which may be outside the visible spectrum.
• Observation angle means the angle having as its sides the line from the observation point to the center of the object to be tested and the line from the center of that object to the center of the source of illumination (Figure 2).
• Reflex reflective means reflective of light in directions close to the direction of incident light, over a wide range of variations in the direction of incident light.

Limits of this page

This page quotes the text of 49 CFR 571.125 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 571.125, Standard No. 125; Warning devices. (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)