What the CDL test really covers
Getting your commercial driver's license comes down to two things: passing the written knowledge tests at the DMV, then passing a skills test in an actual truck. Most people pour all their worry into the skills test, but the knowledge tests are where a lot of folks get tripped up, and they're the part you can fully prepare for from your couch.
- Here's what stands between you and your CDL:
- Knowledge tests you take on a computer at the DMV
- A skills test (vehicle inspection, basic control, and a road drive) in the class of vehicle you want to drive
- Endorsement tests if you plan to haul specific cargo or carry passengers
This guide focuses on the knowledge side, since that's the part you study for.
The knowledge tests you'll take
Everyone starts with the General Knowledge test. It's the core exam, usually around 50 questions, and you'll need about 80% to pass in most states. It covers vehicle inspection, basic control, shifting, space management, and the rules every commercial driver has to know.
- After that, the tests you take depend on what you want to drive and haul:
- General Knowledge, required for every CDL
- Air Brakes, needed for almost any truck with an air brake system
- Combination Vehicles, required for Class A tractor-trailers
- Hazmat, to haul hazardous materials (the H endorsement)
- Tanker, to haul liquids or gases in bulk (the N endorsement)
Not sure which class of license you need? Our guide on what a CDL is breaks down Class A, B, and C in plain language.
How the test is scored
Most states pass you at 80%, so on a 50-question General Knowledge test you can usually miss about 10 and still pass. The exact question count and passing score vary by state, so check your state's page for the specifics. We have a practice test for every state.
The questions are multiple choice. They aren't trick questions, but they're worded carefully, and plenty of the wrong answers look reasonable if you only half-know the material. That's why memorizing answers backfires. You have to understand why an answer is right.
A study plan that actually works
- You don't need months. Most people are ready in two to three weeks of steady study. Here's a plan that works:
- Read one section of the official handbook, then take a short practice quiz on just that section.
- Review every question you miss until the rule makes sense, not just the letter of the answer.
- Retake the quiz until you're scoring 90% or better.
- Move to the next section and repeat.
- Take full-length mock exams in the last few days so the real thing feels familiar.
Short daily sessions beat one long cram session every time. Twenty focused minutes a day adds up faster than you'd think.
Topics that trip people up
- A few subjects show up again and again on the questions people miss:
- Air brakes. The inspection steps and the way the warning systems work catch a lot of people. Slow down and learn them in order.
- Space management. Following distance, stopping distance, and how speed and weight change both.
- Backing and turning. Why you back toward the driver's side and how to set up a turn.
- Pre-trip inspection. You have to know what you're looking at and why it matters.
If you keep missing questions in one area, that's your signal to spend more time there, not less.
From permit to license
- The usual path looks like this:
- Pass a DOT physical and the knowledge tests to get your commercial learner's permit.
- Practice driving on the permit. Federal rules require you to hold it at least 14 days before the skills test.
- Finish entry-level driver training if you're a new applicant.
- Pass the skills test and get your CDL.
Curious about cost and timeline? See how much a CDL costs and how long it takes to get one.
Keep going
- Ready to put this into practice?
- CDL Practice Questions
- CDL Exam Prep Strategy
- CDL Test Tips
- Full CDL Mock Test