Four rules in this part prohibit driving on the basis of the driver’s own condition, and all four operate independently of every credential and every clock the book has covered so far. § 392.3 is the one § 1.4 glossed: no driver shall operate a commercial motor vehicle, and no carrier shall require or permit one to, while the driver’s ability or alertness is so impaired — or so likely to BECOME impaired — through fatigue, illness, or any other cause, as to make it unsafe to begin or continue operating. Two things in that sentence do more work than they look like doing. “Or so likely to become impaired” reaches forward into the trip, so a driver who is fine now and will not be in three hours is already inside the rule. And the relief it allows is narrow and specific: in a case of grave emergency, where the hazard to the vehicle’s occupants or other highway users would be INCREASED by compliance, the driver may continue — but only to the nearest place at which that hazard is removed.

§ 392.4 and § 392.5 are where this chapter and Chapter 9 meet, and the two must not be confused. Chapter 9 taught a testing PROGRAM: who is covered, what triggers a test, what a result means. These are conduct rules at the wheel, they bind whether or not anyone tests anything, and on alcohol the line they draw is far stricter. § 392.5(a) prohibits a driver from using alcohol or being under the influence within 4 hours before going on duty or operating or having physical control of a commercial motor vehicle; from using alcohol, being under the influence, or having ANY MEASURED ALCOHOL CONCENTRATION OR DETECTED PRESENCE of alcohol while on duty or operating or in physical control; and from being on duty or operating while possessing wine, beer or distilled spirits. Two of those three limbs turn on “physical control”, a phrase § 392.5 uses and never defines — nor does anything else in these rules. Read the middle limb again. Chapter 9’s § 382.201 prohibition begins at 0.04 and § 382.505’s stand-down band at 0.02; § 392.5 asks for no number at all — any detected presence is the violation. A driver who is under every Part 382 threshold can be squarely inside § 392.5, and the consequence is immediate: § 392.5(c) places that driver out of service at once for 24 hours, running from the issuance of the order, and no driver may violate its terms.

The out-of-service order then carries duties of its own, on two different clocks. Under § 392.5(d) the driver must report the issuance to their employer within 24 hours, and to a State official designated by the State that issued their driver’s license within 30 days — unless they request a review, in which case the 30 days run from an affirmation of the order. § 392.5(e) gives that review: a written petition to the Division Administrator or State Director for the geographical area within 10 days of issuance, who may affirm or reverse. § 392.4 handles drugs on the same conduct footing — no driver shall be on duty and possess, be under the influence of, or use any Schedule I substance, an amphetamine or any formulation of one, a narcotic drug or any derivative, or any other substance to a degree that renders them incapable of safely operating. Its prescription exception reaches only part of that list, and the boundary matters. § 392.4(c) disapplies paragraphs (a)(2), (3) and (4) — the amphetamine, narcotic and other-substance limbs — where the substance was administered by or under the instructions of a licensed medical practitioner who has advised the driver that it will not affect their ability to operate safely. Paragraph (a)(1), the Schedule I prohibition, is left absolute, exactly as § 382.213(a) leaves it. Where the two rules DO differ is in what the practitioner must have done: § 382.213(b) also required them to be familiar with the driver’s medical history, and § 392.4(c) does not, so satisfying one is not automatically satisfying the other.

Two smaller provisions close the picture. “Possession” in both sections excludes what is manifested and transported as part of a shipment — § 392.4(d) and § 392.5(a)(3)(i) — so hauling a load of beer is not possessing it, and § 392.5 additionally excepts alcohol possessed or used by bus passengers. And § 392.15 links this chapter to the last one in a single sentence: no driver holding a commercial learner’s permit or a commercial driver’s license shall operate a commercial motor vehicle if prohibited by § 382.501(a) — the removal from safety-sensitive functions § 9.5 set out. A Part 382 violation therefore becomes a Part 392 driving offence in its own right, which is why the two chapters are worth holding together rather than filing separately.