CDL Permit Test Study Guide: How to Prepare for the Knowledge Tests

Your state's CDL manual is the study text

The CDL permit test is really a set of knowledge tests, and your state licensing agency writes and gives them. So the first thing to get is the current commercial driver manual from your state's own website, not a copy from another state or an old printout.

Federal rules keep the manuals similar. Each state must give applicants a driver manual comparable to AAMVA's "Model Commercial Driver Manual" (49 CFR 383.131(a)), and its test questions must come from an FMCSA-approved pool comparable to AAMVA's (383.133(b)(1)). That is why most state manuals share the same chapter order. A state may still add its own information (383.131(a)(2)), and your state's version is the one its tests follow.

The federal rule also lists what the tests must cover: 20 general knowledge areas, 7 air brake areas and 3 combination vehicle areas (383.111). It gives no percentages, so no official source says how much of a test comes from each topic.

A study order for the three core CDL knowledge tests

Study the tests in the order you will need them. The section numbers below come from Washington's CDL guide, which follows AAMVA's model numbering. Check the "what to study" table near the front of your own manual before you start, since your state's numbering can differ.

General Knowledge comes first for two reasons. You cannot get a commercial learner's permit without passing it (383.71(a)(2)), and its sections on inspection, speed, space and emergencies feed every other test. Combination Vehicles comes after Air Brakes because the federal combination topics include trailer air brakes (383.111(c)(3)). If you learn the air system first, the trailer chapter reads as an extension rather than a new subject.

When you know which tests you still need and roughly when you will take them, the free CDL study planner builds a dated outline from your test date, and you can fit each manual section into the days you have.

Why each CDL knowledge test needs its own 80%

Federal rules set the passing line test by test: you must answer at least 80% of the questions correctly on each knowledge test (383.135(a)(1)). Two consequences follow:

• Air Brakes: if you fail it and are still issued a permit or license, it carries an air brake restriction (383.135(a)(2)).
• Combination Vehicles: if you fail it, you cannot be issued a Class A (Group A) permit or license (383.135(a)(3)).

Washington's counts, as checked on October 28, 2026, show how this works. General Knowledge has 50 questions with 40 needed to pass, and Air Brakes has 25 with 20 needed. Take a fictional applicant who scores 48 on General Knowledge and 19 on Air Brakes. That is 67 of 75 overall, about 89%, but 19 of 25 is 76%, so the Air Brakes test is failed. Your state's counts may differ, but the federal 80% line applies to each test.

For your study time, that means no test can be left to "catch up later." Give the shorter Air Brakes and Combination chapters full attention, because a few misses there cost more than a few misses on the 50-question test. Weak Spot, planned for full CDL prep, names the test with your lowest accuracy so far, so the weakest test gets the next session.

How CDL test versions change, and why memorized answers fail

Federal rules tell states how to build each version of a knowledge test (383.133(b)(2)):

• 25% of the questions must be new, not used in the previous version.
• Questions carried over must appear in a different position, with their three possible responses in a different order.
• Each version has a set number of questions, with a prescribed number from each knowledge area.
• The difficulty of each version must fall within a set range.

If you fail a test, the state must give you a different version when you retake it (383.133(b)(4)). Memorizing that "the answer is B" or learning a list of questions word for word breaks down under all four rules.

The federal text also explains why "real test" question dumps are not worth your time. The question pool and AAMVA's test documents are material FMCSA approved and provides to state licensing agencies (383.133(b)(1) and (2)), and AAMVA's testing page says it does not distribute its training materials to third parties. A site that claims to sell the real questions cannot show that they come from your state's current pool, and even a correct list would not match the version you get. Original practice is the honest alternative: the 1,650 questions planned for full CDL prep are original, not state or AAMVA items.

A three-pass method for each CDL manual section

Work through each section of your manual in three passes. The method trains the reasoning a reordered or rewritten question still tests.

1. Read for the decision. For each subsection, write one line naming the decision it teaches: when to drain the air tanks, what to do first if your trailer is stuck on railroad tracks, how far ahead to look.
2. Explain it without the book. Close the manual and say the rule and its reason out loud. Keep every number with its condition. "One second for every 10 feet of vehicle length" is only half a rule without "below 40 mph, plus one second above."
3. Check yourself. Answer the review questions printed at the end of the subsection. Washington's guide says those questions may be on your test and tells you to re-read the subsection if you cannot answer them all. Passy does not reuse them, so they are worth doing in your own manual.

Keep two kinds of notes. Numbers go on cards with their conditions attached: tread depths, warning-device distances, air pressures. Judgment calls, such as steering around a hazard instead of braking, go in short scenarios you write yourself. For the numbers, flashcards planned for full CDL prep drill released versus applied leakage limits and other figures with conditions.

Once your General Knowledge, Air Brakes and Combination sections are done, try the 20 free CDL practice questions across all three core tests. Every answer is explained, and the results show how your answers split by test. The set is one fixed mixed set, so use it to choose what to re-read, not to predict a state result.

Where to go next for each CDL test

• Which CDL knowledge tests you need sorts the tests by license class and endorsement.
• The General Knowledge test guide groups the 20 federal areas into six study blocks.
• The Air Brakes test guide lists the seven federal areas and the numbers behind them.
• The Combination Vehicles test guide covers the Class A test.
• How long to study for the CDL permit test helps you budget the weeks before your test date.