Start with a rule that catches drivers arriving from other trades, because it is shorter and stricter than they expect. § 383.21 says no person who operates a commercial motor vehicle shall at any time have more than one driver’s license. Not one commercial license — one license, full stop. A driver cannot hold a personal license in one State and a commercial one in another, cannot keep an old license alive after moving, and cannot carry a spare. The rule exists because the whole enforcement system keys off a single driving record: a second license is a second record, and a second record is somewhere for a conviction to go unnoticed.

§ 383.23 then states what the license is for, in two parts. First, no person may operate a commercial motor vehicle unless they have taken and passed knowledge and driving skills tests meeting the federal standards for the vehicle that person operates or expects to operate. Second, no person may legally operate one unless they possess a commercial driver’s license issued by their State or jurisdiction of domicile. The two are separate requirements and both must hold: passing the tests without holding the license is not enough, and holding a license for a vehicle you were never tested on is not enough either.

The phrase doing quiet work there is “or expects to operate”. The tests attach to the vehicle, not to the job, so the question is never whether you have driven something before but whether your license covers what you are about to climb into. § 383.23(b) provides a narrow non-domiciled route — a non-domiciled commercial learner’s permit or license issued by a State that meets the federal testing and licensing standards — with its own conditions set out in that section. It exists; it is not the ordinary path, and most drivers will never touch it.