What 392.4A-UI means in plain language
392.4A-UI prohibits you from operating a commercial motor vehicle while under the influence of or using a controlled substance, or while impaired by any substance that makes you unable to safely drive. This applies whether you're actively driving or simply in physical control of the vehicle while on duty.
The rule exists because impairment—whether from illegal drugs, prescription medications, or other substances—directly compromises your ability to react, judge distance and speed, maintain lane control, and make safe decisions. A roadside officer citing you for 392.4A-UI has determined, based on their observation and any testing conducted, that a controlled substance or impairing substance was present and affected your capability to operate safely.
Unlike some violations that involve a single equipment failure or paperwork error, this citation targets a condition that regulators treat as an acute safety risk. It carries a severity weight of 10 on the Compliance, Safety, and Accountability (CSA) system—a measure of how much weight FMCSR agencies assign to it when evaluating carrier and driver safety records.
What our enforcement data actually shows
Across our 13 million+ inspection records, 392.4A-UI citations are relatively uncommon by raw volume: 186 all-time citations place this code at rank #1235 out of 3,036 FMCSR codes. However, the enforcement action taken when this violation is cited is extraordinarily consistent.
Our data shows a 98.9% out-of-service (OOS) rate for 392.4A-UI—meaning inspectors removed drivers from duty in 184 of the 186 cases on record. For context, the all-FMCSR average OOS rate is 31.4%. This code's rate is more than three times higher, reflecting how seriously enforcement treats drug-impairment violations at the roadside.
In the last 12 months, we recorded 97 citations. Over the past 90 days, 14 new citations have appeared in our database. Monthly citation counts have ranged from 5 (January 2026) to 21 (May 2025), with no clear upward or downward trend. The consistency of near-universal OOS placement, however, remains unchanged regardless of citation volume.
Who gets cited most
Our last 180 days of data show three states leading in citation count: Iowa with 24 citations (95.8% OOS rate), North Carolina with 4 citations (100.0% OOS rate), and Illinois with 3 citations (100.0% OOS rate). The variation in OOS rates across these states is minimal; Iowa's 95.8% rate is slightly below the national 98.9% figure, while both North Carolina and Illinois hit 100%.
By carrier, no single fleet stands out with high frequency. Our data shows carriers such as Valcam Express Corporation and Royal Trucking Company each with 2 citations, but the majority of citations are distributed across many different operations with only 1 recorded case each. This pattern suggests that 392.4A-UI citations are spread across the industry rather than concentrated in a few carriers.
How severe is this compared to similar codes
392.4A-UI falls within the controlled substances and alcohol category, alongside several related codes. To understand where it sits in the enforcement spectrum:
392.4A-DOSP (Use of drugs) has 3,947 citations with a 95.9% OOS rate—far higher citation volume but a slightly lower OOS rate.
392.4A-POS (Use of drugs) shows 655 citations with a 97.6% OOS rate—again, higher volume but comparable OOS severity.
392.5(a)(2) (BAC 0.04+) accounts for 778 citations with a 99.2% OOS rate—similar raw numbers but slightly higher OOS consistency.
The common thread is clear: all codes in this category carry OOS rates in the 95–99% range, far exceeding the all-FMCSR average. Your 392.4A-UI citation reflects an enforcement posture that treats any suspected drug impairment as a grounds for immediate removal from service.
How to avoid it
The most direct prevention strategy is to never operate while impaired by any substance. However, our co-occurring violation data reveals patterns worth understanding:
Fatigue and illness often occur together with drug-related citations. Our records show 392.2RG (Operating while ill or fatigued) and 392.2C (Operating while ill or fatigued) appearing in 4 and 3 inspections respectively alongside 392.4A-UI cases over the past 90 days. If you are fatigued, ill, or taking medications that impair alertness, you should not be operating. Do not attempt to self-medicate with substances to overcome fatigue—that choice multiplies your violation exposure.
Mechanical and logistical violations cluster with drug citations. False record of duty status, equipment defects, and missing endorsements appear in the same inspections as 392.4A-UI, suggesting that impaired drivers are also more likely to cut corners in pre-trip inspections and compliance. Make a genuine pre-trip inspection part of every shift start:
- Walk around your vehicle and check lights, brakes, and emergency equipment before leaving the lot.
- Review your logbook and ensure your hours-of-service entries are accurate and honest.
- If you are taking any prescription or over-the-counter medication, consult your doctor or pharmacist about whether it is safe to operate a CMV. Many medications carry warnings about operating machinery.
- If you feel fatigued, ill, or otherwise impaired, inform your dispatcher and take time off. No load is worth an OOS violation and the safety risk it represents.
Vehicle make patterns offer limited prevention insight, but Freightliner trucks account for 41 of the 186 all-time citations, followed by International (33) and Peterbilt (21). This reflects the market share of these makes in trucking, not a defect specific to those vehicles. Maintenance of your specific truck's systems remains your responsibility.
Bottom line: if you have been cited for 392.4A-UI, you were removed from service immediately and face serious carrier and CSA consequences. The best defense is to never operate impaired and to be honest about your physical and mental readiness before each shift.