The single most common misunderstanding we see from people starting out is that there is a CDL test, one thing, that you pass or fail. There is not. There are up to eight separate written tests, you sit the ones your situation calls for, and each is scored on its own.
Getting this straight first saves a surprising amount of wasted study.
The eight tests
Three of them are core knowledge tests, and the rest are add-ons tied to what you will carry or drive.
- General Knowledge is the one everybody takes. Passing it is what earns your commercial learner's permit.
- Air Brakes is a restriction removal rather than an endorsement. Skip it, or fail it, and your license is issued with a restriction barring you from air-braked vehicles. Nothing is added when you pass; something is removed.
- Combination Vehicles is a core knowledge test for Class A, not an add-on.
- HazMat (H), Tanker (N), Passenger (P), School Bus (S) and Doubles/Triples (T) are the five knowledge-tested endorsements.
That distinction matters because people routinely describe Air Brakes and Combination Vehicles as endorsements. Only H, N, P, S, T and X are endorsements, and X is just the combination of H and N on one credential.
How the questions are drawn
Under 49 CFR 383.133, each test must draw a set number of questions from a pool approved for that state, and the pool has to cover the required knowledge areas. What the regulation does not do is publish a single number of questions per test for every state.
That is why you will find sites confidently stating that the HazMat test is 30 questions, and other sites saying 20. The honest answer is that your state sets the length, and the only reliable source for your state's number is your state's own CDL manual or licensing agency.
What is consistent: the pass mark is 80 percent, and the questions come from your state's CDL manual. Not from trucking experience, not from what a driver told you at a truck stop. The manual.
What 80 percent means in practice
On a short endorsement test, 80 percent is less forgiving than it sounds. If your state gives a 20-question HazMat test, you can miss four. On a 30-question test you can miss six. There is no partial credit and no curve.
This is the argument for taking practice tests rather than just reading. Reading a manual section produces a feeling of understanding that does not survive contact with a question written to separate two similar answers.
Failing one test does not fail the rest
The tests are scored separately, so failing Air Brakes does not take away a General Knowledge pass you already have. States set their own retest rules, including waiting periods and fees, and those vary enough that it is worth knowing yours before you book.
Our CDL cost by state page lists published fees by category, including knowledge test fees where the state publishes them.
Where to start
Work out which class you need first, because it decides which tests you sit. The CDL Selector does that from a few questions, and CDL classes A, B and C explains the weight ratings behind them.
Then test yourself before you study, not after. A free General Knowledge practice test takes a few minutes and tells you which manual sections you actually need to read. Every one of the eight tests has a free practice version on the practice test hub.
Last verified November 11, 2026.