This book has cited § 390.3T and § 390.5T since the second sentence of § 1.1, with a note saying only that the T forms are the ones in force. Here is the whole of it, because it is the most useful thing in this chapter. § 390.3 and § 390.5 exist. They are fully written. They carry the general applicability rule and the definitions the entire subchapter turns on, they read exactly like every other section in this book, and they are SUSPENDED. The pinned text says so in a note appended after the section: § 390.3 was suspended effective January 14, 2017, the suspension was lifted and the section amended and again suspended indefinitely effective November 8, 2021. § 390.5 carries the same kind of note and a longer history — suspended effective January 14, 2017, then lifted, amended and re-suspended indefinitely again in 2019, twice in 2021, in 2022, twice in 2023, and again in July 2026.

Sit with what that means for someone looking a rule up. There is nothing in the body of § 390.5 that announces it is not operative. A driver, a dispatcher or a compliance officer who searched for the definition of commercial motor vehicle, found § 390.5, read it carefully and acted on it would have read attentively and been wrong — and the parallel section that IS in force sits a few lines further down under a number one character different. This book cites the T forms because a pinned snapshot let it check; nothing about the more obvious number warns you. That is the argument for the habit, and it is a better argument than any general observation about regulations changing, because it is not about the future at all. It is about a section that is sitting there right now, looking authoritative.

So the discipline to carry out of this book is narrow and worth the trouble: before you rely on a rule that matters, confirm it against the current official text rather than the version you remember or the version you have to hand. Give the most attention to the parts that decide outcomes — a number, a threshold, a period, a date — because those are what changes when a section is amended and those are what a stale copy gets wrong most expensively. The same evidence is scattered through everything you have read: § 8.2’s electronic logging requirement carries a compliance date, § 8.1’s supporting-document rules took effect on one, § 3.4’s training requirement has one, and nearly every section in the corpus ends in a bracket listing the amendments that made it what it is. A rulebook is a photograph of a moving thing.

That is also the promise this book is built on rather than a caution appended to it. It is assembled from pinned snapshots of the official text, every claim in it traces to one, and when the underlying rule changes the book is meant to change with it. What you should not do is treat any printed thing — this one included — as the final authority on a number you are about to act on. Look it up. The whole of § 12.4’s classification skill comes down to the same instinct: know which questions have lookup-able answers, and then actually look them up.