What 392.4(b) means in plain language
FMCSR 392.4(b) is a federal rule that makes it illegal for you to have a controlled substance in your possession while you are on duty or actively operating a commercial motor vehicle. The regulation applies to any drug classified as a controlled substance under federal law—including prescription medications you may not have a valid prescription for, or any illegal drugs.
"On duty" means any time you are working as a driver, even if the engine isn't running. "Operating" means you are actively driving the vehicle. The violation occurs the moment you are found in possession of the prohibited substance during either of these states. This is distinct from actually using or being impaired by a drug, which are separate violations under other FMCSR codes.
The rule exists because the Federal Motor Carrier Safety Administration treats drug possession as a safety risk—the presence of controlled substances in a commercial driver's possession creates liability for the driver and the carrier, and indicates a heightened risk of impairment or distraction.
What our enforcement data actually shows
Our inspection records show that 392.4(b) citations are extremely rare in practice. Across our database of 13 million+ roadside inspections, we have recorded zero citations for possession of drugs under this specific code all-time, in the last 12 months, and in the last 90 days. This means the violation is either not being enforced at roadside through CVSA inspections, or enforcement is so infrequent it does not appear in our dataset.
Because the citation count is zero, we cannot calculate an out-of-service rate for this code. However, 392.4(b) is eligible for out-of-service placement if cited—meaning an officer has the authority to remove you from service immediately if you are found in violation.
The rarity of 392.4(b) citations does not mean the rule is unenforced. Many possession cases are handled outside the roadside inspection context—through law enforcement traffic stops, facility inspections, or pre-employment screening. If you are cited for drug possession, the consequences are typically severe and extend beyond roadside inspection data.
Who gets cited most
Given zero citations recorded in our system, state-by-state and carrier-by-carrier breakdowns are not available. This code does not appear in the top violation categories across any state in our 13 million-inspection database.
How severe is this compared to similar codes
While 392.4(b) itself shows zero citations in our records, the related possession and use violations show a very different pattern. Our data shows that similar codes in the controlled substances category are cited far more frequently:
- 392.4A-DOSP (Use of drugs) has 3,947 citations in our database with a 95.9% out-of-service rate.
- 392.4(a) (Use of drugs) accounts for 3,919 citations with a 96.9% out-of-service rate.
- 392.4A-DOSU (Use of drugs) has 1,648 citations with a 98.5% out-of-service rate.
All of these peer codes show OOS rates in the 95–99% range, meaning nearly every citation results in immediate out-of-service placement. This underscores that violations in the controlled substances category are treated as critical safety events by enforcement officers.
Alcohol-related possession codes show similarly high OOS rates: 392.5(a)(3) (Driver possession of alcohol while on duty) has 1,301 citations with a 98.2% OOS rate, and 392.5(a)(2) (BAC 0.04+) has 778 citations with a 99.2% OOS rate. The pattern is clear: possession and use of drugs or alcohol on duty are near-automatic out-of-service violations.
How to avoid it
The safest approach is to ensure you never have controlled substances in your vehicle or person while on duty or operating a CMV:
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Leave medications and personal items at home or in a secure location. Before each trip, review your vehicle and belongings. Remove any prescription medications that are not actively prescribed to you, or any substances that could be misidentified. Carry only what you need for the duration of your duty time.
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If you take prescription medications, carry documentation. Bring the original prescription bottle or a letter from your physician confirming the medication is prescribed to you and that you are authorized to take it while driving. Some medications are incompatible with safe driving; consult your doctor about your fitness to drive while taking any new medication.
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Understand what "on duty" means for you. Even if you are resting or eating at a truck stop, you may be considered on duty. Drug possession during any on-duty period is a violation. If you use any medication during a 34-hour reset or off-duty period, ensure you are not on-duty status and that the substance is secured in a manner that makes it clear it is not accessible to you while operating.
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Know federal vs. state law. Some states have legalized cannabis, but it remains a Schedule I controlled substance under federal law. Possession of marijuana is a federal violation for any commercial driver, regardless of state law. Do not carry it.
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Decline rides or cargo from drivers or shippers offering substances. If you are asked to transport or carry items that appear to be controlled substances, refuse. Report the request to your carrier and law enforcement if necessary.
The fact that 392.4(b) citations are rare in our roadside data does not mean the rule is lenient. Rather, it may reflect that drivers are avoiding the violation, or that enforcement is occurring through other channels. Either way, the safest course is simple: do not possess controlled substances while on duty or operating a commercial vehicle.