Lesson 01 · 5 min
Separate the alcohol rules on the duty timeline
Choose the rule that applies before duty, during duty, and after an alcohol-prohibition violation.
Rule to rememberDo not perform safety-sensitive work within four hours after alcohol use. Any measured concentration or detected presence while on duty or controlling a CMV violates § 392.5 and can cause a 24-hour out-of-service order; 0.04 is a separate disqualification threshold.
Before duty
The four-hour rule is a minimum time bar, not a promise that a driver is fit after four hours. A driver must not report for or perform safety-sensitive work if alcohol still affects safe operation.
During duty
Section 392.5 prohibits alcohol use, influence, any measured concentration, or detected presence while on duty or operating or controlling a CMV.
Keep consequences separate
A § 392.5 violation brings an immediate 24-hour out-of-service order. An alcohol concentration of 0.04 or greater while operating a CMV is also a major offense under the CDL disqualification table.
Sources
49 CFR 392.5 — Alcohol prohibition · 392.5(a)–(c) · recorded date 2026-09-07 ↗49 CFR Part 382, Subpart B — Prohibitions · 382.201–382.217 · recorded date 2026-09-07 ↗49 CFR 383.51 — Disqualification of drivers · 383.51(a)–(b), Table 1 · recorded date 2026-09-07 ↗49 CFR 382.301 and 382.501 — Testing and removal · 382.301; 382.501 · recorded date 2026-09-07 ↗