The alcohol prohibitions are three separate rules, and a driver who knows only the first has two blind spots. § 382.201 sets the concentration: no driver shall report for duty or remain on duty requiring the performance of safety-sensitive functions while having an alcohol concentration of 0.04 or greater. § 382.205 forbids using alcohol at all while performing safety-sensitive functions — no concentration is named there, because the act is the violation. And § 382.207 reaches backwards before the shift: no driver shall perform safety-sensitive functions within four hours after using alcohol. Read them against § 9.1’s definition and the four hours are longer than they look, because a safety-sensitive function starts at waiting to be dispatched and at inspecting the vehicle, not at the driving controls. Each of the three binds the employer as well: an employer with knowledge of the concentration, or actual knowledge of the use, may not permit the driver to perform or continue to perform.

Controlled substances work differently, and § 382.213 draws the line at the prescription rather than at a number. A driver may not report for or remain on duty requiring safety-sensitive functions while using any drug or substance in Schedule I — the federal classification of controlled substances runs from Schedule I through Schedule V — and no exception is offered there. For substances in the other schedules the exception exists but is narrow, and its narrowness is the whole point: the use must be prescribed by a licensed medical practitioner who is familiar with the driver’s medical history AND who has advised the driver that the substance will not adversely affect their ability to operate a commercial motor vehicle safely. Both halves are required. A valid prescription from a practitioner who does not know what the driver does for a living satisfies neither. The same test binds the employer with actual knowledge, and § 382.213(d) permits an employer to require a driver to inform it of any therapeutic drug use.

One band sits between the two alcohol rules and it is the figure drivers most often have not heard of. § 382.505(a) provides that a driver tested under subpart C who is found to have an alcohol concentration of 0.02 or greater but less than 0.04 shall not perform or continue to perform safety-sensitive functions, and no employer shall permit them to, until the start of that driver’s next regularly scheduled duty period — but not less than 24 hours following administration of the test. Below 0.02 the part goes the other way: § 382.505(b) provides that, apart from that band, no employer shall take any action under this part against a driver based solely on a test result showing a concentration under 0.04, though an employer with authority independent of this part may act consistently with law. So the reading a driver needs is not one line but three: under 0.02 the part authorizes nothing on the result alone, from 0.02 to below 0.04 a stand-down of at least 24 hours, and at 0.04 or above the § 382.201 prohibition.

The fifth prohibition is the one drivers underestimate, because it feels procedural rather than substantive. § 382.211 states that no driver shall refuse to submit to a pre-employment controlled substance test, a post-accident alcohol or controlled substance test, a random test, a reasonable suspicion test, a return-to-duty test, or a follow-up test — six kinds, named individually so there is no argument about which are covered — and that no employer shall permit a driver who refuses to perform or continue to perform safety-sensitive functions. Refusing is not declining to participate in a process; it is prohibited conduct sitting in the same subpart as driving with alcohol in your system, and § 9.5 sets out what follows from any violation in that subpart.