§392.3 prohibits a driver from operating a CMV — and a carrier from requiring or permitting it — while the driver's ability or alertness is so impaired, or so likely to become impaired, through fatigue, illness, or any other cause that it is unsafe to begin or continue. The only exception is a grave emergency where stopping would increase the hazard, and then only to the nearest place the hazard is removed. The rule reaches further than the hours limits — a driver who is technically within hours but visibly impaired is still in violation.
Severity weight
Severity weight 10 in the Hours-of-Service Compliance BASIC. SMS Appendix A (version 3.21, revised May 2026) places §392.3 and its four fatigue and illness codes (392.3-F, -FPASS, -FPROP, -I) in the HOS Compliance table's "Jumping OOS/Driving Fatigued" group — that table's maximum weight. It is not an Unsafe Driving violation, and FMCSA's Appendix A overview says severity weights reflect relative crash risk within a BASIC and are not comparable across BASICs, so a §392.3 citation lands on the carrier's HOS Compliance measure, not Unsafe Driving.
OOS
The 392.3 placement-out-of-service is for 10 consecutive hours. The driver cannot resume driving until that period expires, and the carrier must document the corrective action.
How to prevent it
- Train drivers and dispatchers that "I'm fine" is not a defense at roadside — observable signs (slurred speech, swerving, falling asleep at a stoplight) are what officers cite.
- Build a no-questions-asked layover policy and pay for it. Drivers who can't afford to stop will drive impaired.
- Document medical conditions and medications in coordination with the §391.43 medical examiner; sedating prescriptions can be disqualifying.
How Roadworthy HQ helps
A §392.3 citation lands on the driver. Roadworthy HQ does not record individual violation codes, pull CSA or SMS scores, or track coaching. What it keeps is the driver file an auditor opens next: the annual MVR and the §391.25 annual review, each with reminders 60, 30, and 7 days out, and the qualification-file documents with their retention periods enforced. If the citation came from a roadside inspection, log that inspection on the vehicle (date, state, level, driver, number of violations, out-of-service or not).