What 172.338 means in plain language
When you transport hazardous materials, every placard on your vehicle must display the proper UN or NA identification number. This four-digit number tells emergency responders and law enforcement exactly what chemical, gas, liquid, or solid is on board. If that ID number is missing, faded beyond legibility, or damaged so it can't be read, your carrier is in violation of 172.338.
The regulation requires that ID numbers stay visible and intact throughout transport. A missing number doesn't mean the placard itself is gone—it means the placard exists but the critical ID digits are absent or illegible. This creates a serious gap in hazard communication, even if the general hazard class placard (like "Flammable Liquid") is still visible.
What our enforcement data actually shows
Across our 13 million+ inspection records, 172.338 is cited rarely. We see 16 all-time citations in our database, with just 1 citation in the last 12 months and 0 citations in the last 90 days. This places the code at rank #2026 out of 3,036 FMCSR violations—a very low-frequency citation.
When this violation is cited, inspectors place vehicles out of service only 12.5% of the time (2 OOS placements out of 16 total citations). That's substantially lower than the all-FMCSR average OOS rate of 31.4%, indicating inspectors view this as a moderate hazmat documentation issue rather than an immediate safety emergency in most cases.
The one citation logged in the last 12 months occurred in July 2025, and that vehicle was placed out of service.
Who gets cited most
Our records do not break down 172.338 citations by state, so we cannot identify which states have the highest incidence. However, our data shows that individual carriers such as Alberto Vazquez Perez (USDOT 3260169) have received 2 citations under this code—the highest count in our database—while nine other carriers have each received 1 citation. The top vehicle makes cited include International (4 citations), Freightliner (2 citations), and Kenworth (2 citations), suggesting this violation appears across a broad range of truck types and operators rather than concentrating in a single carrier segment.
How severe is this compared to similar codes
Hazmat ID and placarding violations span a wide severity range. Our data reveals dramatic differences within the category:
General loading and unloading hazmat violations (codes 177.834A-HMC and 177.834(a)) are cited far more often—3,954 and 3,839 times respectively—and result in out-of-service placement over 97% of the time. These represent critical hazard handling failures.
Placard deterioration (172.516(c)(6)) is cited 1,796 times with only a 1.6% OOS rate, very similar to 172.338's 12.5% rate. This suggests inspectors distinguish between a missing ID number and a merely degraded placard, but both are treated as documentation issues rather than catastrophic hazards.
General placarding requirements (172.502(a)(1)) appears 1,820 times with an 18.5% OOS rate—slightly higher than 172.338, indicating that broader placarding failures are somewhat more likely to trigger immediate removal.
How to avoid it
Preventing a 172.338 citation requires attention to placard condition before and during every trip:
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Inspect all four sides of your vehicle during pre-trip. Walk around the entire rig and verify that every placard is fully attached, and that the UN or NA ID number (the four-digit code in the middle or below the hazard class symbol) is completely legible. Look for fading, peeling labels, or weathering that obscures the numbers.
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Check placards after fueling, weather events, or highway driving. Wind, vibration, and moisture can loosen placards or degrade printed ID numbers. A quick visual check after a fuel stop or rough highway section takes 30 seconds and prevents citations.
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Replace, don't cover or repair. If an ID number is illegible or missing, remove the entire placard and apply a new one. Do not attempt to rewrite, repaint, or patch the number yourself. A placard must meet DOT labeling specifications for visibility and durability.
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Verify your manifest matches your placards. Before departure, confirm that the ID numbers on your placards align with the hazmat commodity codes on your shipping papers. A mismatch can lead to an inspector questioning whether the correct ID number is even present.
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Secure placards with weather-resistant fasteners. Use clips, adhesive, or holders designed for outdoor transport. Flimsy attachment methods fail under road vibration and environmental stress.
The low citation rate (1 in the last 12 months) suggests that most carriers maintain placard standards, but vigilance during pre-trip inspection is your first and best defense.