Which CDL knowledge tests do you actually have to pass?

The commercial licence is modular. There is no single "CDL test" — there is a stack of written tests, and which ones you sit depends on the class of licence and what you intend to drive.

Get the stack right before you start studying. People lose weeks preparing for a test they did not need, or turn up having skipped one they did.

The classes

Class A — combination vehicles: a tractor with a trailer over 10,000 lb. This is the licence for over-the-road trucking, and it requires the most tests.

Class B — a single heavy vehicle: a straight truck, a dump truck, a city bus. No large trailer.

Class C — smaller vehicles that still need a CDL because of what they carry: hazardous materials, or 16 or more passengers.

The written tests

General Knowledge. Everyone takes it, in every class. Vehicle inspection, basic control, shifting, seeing hazards, distracted and aggressive driving, night and winter driving, mountain driving, railroad crossings, accident procedures, cargo securement, and the medical and alcohol rules.

Air Brakes. Required if the vehicle you will drive has air brakes — which is most heavy trucks. Skip this test, or fail it, and your licence carries an L restriction: no air brakes until you come back and pass. That restriction closes the door on most trucking jobs, so treat it as mandatory even where it technically is not.

Combination Vehicles. Required for Class A. Coupling and uncoupling, trailer brakes, the emergency and service air lines, and how a combination behaves differently from a single unit — off-tracking, rearward amplification, jackknifing.

Endorsements, if the job needs them

• T — double and triple trailers
• P — passenger vehicles
• S — school bus, on top of P
• N — tank vehicles
• H — hazardous materials, which also requires a federal background check
• X — tank and hazmat combined

Each is its own written test. Take them when a job requires them; there is nothing to gain from collecting them.

The shape of the questions

CDL knowledge questions are typically multiple choice with three options, not four. Small detail, real consequence: a guess pays better than it does on a four-option test, and the wrong options sit closer to the truth. Practice in the three-option format so the shape is familiar before test day.

You also sit a pre-trip inspection and a skills test in the actual vehicle. Those are not written, but the General Knowledge material is exactly what the examiner asks you to recite while walking around the truck — study it once, use it twice.

Where the questions come from

Almost every state builds its CDL manual from the AAMVA model manual, so the material is close to identical across state lines and the numbers — brake pressures, inspection steps, cargo rules — usually match. Get your own state's manual anyway. It is free, it is a PDF, and it is the exact source your examiner is working from.