CDL study guide
The manual tells you what is on the test. It does not tell you what to do on Tuesday. This is the schedule — three weeks, an hour a day, built around the one habit that separates people who pass from people who resit: studying what you get wrong instead of what you already know.
Before you open anything
Work out which written tests you are sitting, because studying for tests you do not need is the most common way to waste two weeks. Everyone takes general knowledge. Beyond that:
- Class A adds combination vehicles, and air brakes if you want to drive anything with them — which is nearly everything.
- Class B adds air brakes, plus passenger and school bus if you are going into buses.
- Endorsements are one written test each. HazMat additionally needs a TSA security threat assessment — start that early, because the background check is on somebody else's schedule, not yours.
Not sure which class you need? The class comparison decides it on two weight numbers.
The three weeks
Week 1 — map it
- Read the general knowledge sections of your state manual end to end once, without taking notes. You are mapping the territory, not memorising it.
- Take the general knowledge practice test in Quick mode (10 questions) twice a day. Ignore the score — you are finding out which sections you cannot answer at all.
- Write down every question you missed. By day three that list is your syllabus.
Week 2 — close the gaps
- Re-read only the sections your missed questions came from. Everything else you already know.
- Switch to Full mode — all 52 general knowledge questions in one sitting — every other day.
- Start the pre-trip inspection test. It is the part of the exam people fail, and it is memorisation, so it needs the most repetitions.
- Add your endorsements now, one bank at a time. Doing two at once blurs them together.
Week 3 — test conditions
- Full general knowledge test daily until you clear 90% three times running. The real pass mark is 80%, and you want headroom for exam nerves.
- Say the pre-trip out loud, walking around a vehicle if you can get to one. Reciting it in your head does not transfer to standing in front of an examiner.
- Take each endorsement test cold, without revision that day. Cold is the condition you will be tested in.
- Stop studying the night before. There is nothing left to add and tired is the most common preventable failure.
Two weeks instead of three? Drop week one. Go straight to practice questions and let the wrong answers send you into the manual. It is less comfortable and it works about as well — reading first mostly buys confidence, not marks.
The numbers you have to know cold
Almost every general knowledge test leans on the same handful of figures. If you know nothing else on the morning of the exam, know these.
| Steer tire tread depth | 4/32 inch in every major groove |
| All other tires | 2/32 inch |
| Following distance under 40 mph | 1 second for every 10 feet of vehicle length |
| Following distance over 40 mph | The same, plus 1 second |
| Look-ahead distance | 12 to 15 seconds — about a quarter mile at highway speed |
| Legal BAC limit, CDL holder | 0.04% — half the non-commercial limit |
| Warning devices, level straight road | 10 feet, 100 feet and 200 feet to the rear |
| High beams | Dim within 500 feet of an oncoming vehicle, or following within 500 feet |
| Commercial learner’s permit | Held at least 14 days before the skills test |
Federal figures, from the same source material the state manuals are written from. Where a state sets its own rule — permit fees, hold times beyond the federal minimum, intrastate age — the state manual wins, and it is the document your test comes from.
What to drill, in order
| Test | Bank | Why it is where it is |
|---|---|---|
| General knowledge | 52 questions | Everyone takes this one, whatever class you are going for. |
| Pre-trip inspection | 41 questions | Recall, not reasoning — and the single most failed part of the exam. |
| Air brakes | 22 questions | Skip it and you get an "L" restriction that keeps you out of most trucks. |
| Combination vehicles | 20 questions | Required for Class A. Coupling, uncoupling, trailer brakes. |
| HazMat (H) | 50 questions | The biggest bank here, and the endorsement that pays the most. |
| Tanker (N) | 16 questions | Surge, baffles, and why you brake early with liquid behind you. |
| Passenger (P) | 16 questions | Buses, loading, and the rules that change when people are the cargo. |
| Doubles/triples (T) | 16 questions | Coupling order and the crack-the-whip effect. |
| School bus (S) | 16 questions | Sits on top of P. Danger zones, evacuation, railroad crossings. |
How to read the manual so it sticks
The manual is written as reference material, and reference material is terrible to study from front to back. Three things make it behave:
- Read the section headings first. Twenty minutes knowing what exists beats two hours reading page one to page forty.
- Answer before you read. Take the practice test on a section you have not studied. Getting it wrong first makes the correct answer stick in a way that reading it first never does.
- Explain it to someone. Anyone. If you cannot say why you dim your high beams at 500 feet without looking it up, you have not learned it — you have recognised it, and recognition disappears under exam pressure.
The part nobody studies for
The written tests are the easy half. The skills test is where the resits happen, and the pre-trip inspection is where the skills test goes wrong — it is a recall exercise performed out loud, in front of an examiner, under time pressure. It is also the only part of the skills test you can genuinely prepare for at a kitchen table.
Start it in week two, not week three. Read the zone-by-zone walkthrough, then drill the pre-trip questions until the order comes without thinking.
The other deadline
A valid medical certificate has to be on file before you can be licensed, and since the National Registry rule the examiner sends it to your state — you do not. Book the DOT physical in week one. People who leave it until they have passed the written tests are the people who end up waiting on paperwork with a permit clock running.
Common questions
How long should I study for the CDL written test?
Two to three weeks at an hour a day is enough for most people to pass general knowledge and one endorsement. The variable is not intelligence, it is whether you study the sections you get wrong or re-read the ones you already know — which is what most people do, because it feels better.
Do I have to read the whole CDL manual?
Once, quickly, yes. Then never again cover to cover. The efficient pattern is: read it through once to know what is in it, then let practice questions tell you which sections to go back to. Your state publishes its own manual and it is the document your test is written from, so use that one rather than a generic PDF.
What score do I need to pass?
80% on each knowledge test in every state. Aim for 90% in practice — the gap absorbs exam nerves and the two or three questions that are worded differently from anything you have seen.
Which tests do I actually have to take?
General knowledge for every class. Add air brakes if the vehicle has them, combination vehicles for Class A, and one written test per endorsement. HazMat also adds a TSA security threat assessment, which is a background check and fingerprints, not a study problem.
Should I study for the skills test at the same time?
Only the pre-trip inspection, which is half memorised script and worth starting early. Basic controls and the road test are muscle memory — they come from seat time, and no amount of reading substitutes for it.
Is the practice test the same as the real exam?
No, and nothing that claims to be is telling you the truth. Questions here are written from the federal material the state manuals are built on, so the facts and the numbers match. The wording on exam day will be different, which is the point — memorising answers to specific questions is how people fail a test they had been scoring 95% on.