It is worth being precise, this late in the book, about what the thing you have been reading actually covers. § 390.3T(a)(1) says it plainly: the rules in this subchapter apply to all employers, employees and commercial motor vehicles that transport property or passengers in INTERSTATE COMMERCE. That is the subject — safety of operation — and § 2.2 spent a section on what the boundary means. § 390.3T(b) then extends the license rules across it, into intrastate commerce, which is the asymmetry § 1.1 asked you to carry from the first page. Everything else in this book has been detail hung on those two sentences.

The subchapter is equally clear about three things it does NOT settle itself, and each hands the question somewhere different. It hands one ELSEWHERE IN THE REGULATIONS: § 390.3T(c) addresses financial responsibility for motor carriers by pointing at Part 387, as provided in § 387.3 or § 387.27 — a part that is not among this book’s sources, so what it requires is not something this book can tell you. It hands one TO YOUR EMPLOYER: § 390.3T(d) provides that nothing in the subchapter shall be construed to prohibit an employer from requiring and enforcing MORE STRINGENT requirements relating to safety of operation and employee safety and health. A carrier rule tighter than the federal one is therefore not in conflict with these regulations — so meeting a requirement your employer sets that this book does not contain is not evidence that either the employer or the book has got something wrong. And it hands one TO THE STATES: § 390.9 leaves State and local safety law standing so long as complying with it would not prevent full federal compliance. § 2.1 taught that structure and § 10.1 taught which governs at the wheel; this book teaches the federal rules, and it does not tell you what any particular State requires.

What it does not hand off is the duty to know. § 390.3T(e) puts that on both sides of the relationship in consecutive sentences: every employer shall be knowledgeable of and comply with all regulations in the subchapter applicable to that carrier’s operations, and every driver and employee shall be INSTRUCTED REGARDING, and shall comply with, all applicable regulations. Read the driver’s half carefully, because it is doing two things. Being instructed is something owed TO you — the carrier’s side of § 12.3’s bargain — and complying is owed BY you, and the section does not make the second conditional on the first. Nobody in that chain gets to treat the rulebook as somebody else’s responsibility, which is where § 1.1 started.

The practical skill this leaves you with is not memory but classification: knowing which KIND of question you are holding. Is it one this rulebook answers, and can be looked up? Is it one the regulations answer somewhere this book does not go? Is it one your employer is entitled to answer more strictly than the federal rule? Or is it one that belongs to the State you are driving in? Four different questions, four different places to look, and the most expensive mistakes come from asking the first place for an answer that was never going to be there.