What a Commercial Driver's License Knowledge Test Covers
The commercial driver's license (CDL) knowledge test is a written exam administered by your state's Department of Motor Vehicles that measures your understanding of the rules, safety practices, and vehicle operation specific to commercial trucks and buses. The test is not the same as a regular driver's license exam — it covers air brakes, hazardous materials, passenger safety, and vehicle inspection in ways that a standard driving test does not.
Your state's DMV publishes the official CDL manual, which contains all the material the test draws from. The manual is free and available online through your state DMV website, usually as a PDF read. Some states also offer printed copies at DMV offices. The test itself typically contains 50 questions, though the exact number varies by state and by which CDL endorsement you are pursuing.
You must pass the knowledge test before you can take the skills test (the driving portion). Many people take a practice test multiple times to build confidence and identify weak areas before sitting for the official exam at the DMV.
Key Takeaways
- Your state DMV publishes the official CDL manual for free online, and the knowledge test draws only from material in that manual.
- Practice tests mimic the format and difficulty of the real exam but do not determine whether you will pass — only the official DMV test does.
- Different CDL classes and endorsements (passenger, hazmat, tanker) have different test sections, so confirm which one you need before you study.
- Most states require you to score 80 percent or higher to pass, though the exact passing score varies by state and endorsement type.
- You can retake the knowledge test if you fail, but your state may require you to wait a certain number of days between attempts.
How to Find Your State's Official CDL Manual and Practice Materials
Start by visiting your state DMV website and searching for "CDL manual" or "commercial driver's license handbook." Most states host the manual as a free PDF that you can read online or read to your computer. Some states also offer the manual in Spanish and other languages. The manual is organized by topic — general knowledge, air brakes, passenger transport, hazardous materials — so you can study one section at a time.
Many state DMVs also publish sample questions or a practice test on their website. These official samples are the most reliable because they come directly from the agency that writes the real test. Search your state DMV site for "CDL practice test" or "sample questions." Some states embed these in their website; others link to a separate testing platform. A few states do not offer an official practice test online, in which case you will need to use a third-party resource.
Your state DMV office may also have printed copies of the manual and practice materials available in person. If you prefer to study on paper or want to confirm you have the most current version, calling your local DMV office can tell you whether they stock these materials and whether there is a cost.
What Topics Appear on the CDL Knowledge Test
The CDL knowledge test is divided into sections based on the type of commercial driving you plan to do. The general knowledge section covers rules of the road, vehicle inspection, safe driving practices, and what to do in an emergency. This section is required for all CDL applicants.
If you are pursuing a passenger endorsement (to drive buses or vans carrying passengers), you will answer additional questions about passenger safety, loading procedures, and how to handle emergencies with people on board. If you are pursuing a hazardous materials endorsement (to transport chemicals, fuel, or other regulated substances), the test includes questions about labeling, placarding, loading rules, and what to do if there is a spill or leak.
Other endorsements — such as tanker, double/triple trailer, or air brake — each have their own test sections. Your state DMV website will tell you which endorsements are available and which sections you need to study. If you are unsure which endorsement you need, contact your employer or the company that will hire you, as they can specify what your job requires.
How Practice Tests Work and What They Show You
A practice test mimics the format of the real DMV exam: multiple-choice questions, the same number of questions per section, and similar wording and difficulty. Taking a practice test helps you become familiar with how questions are phrased, which topics appear most often, and where your knowledge gaps are. Many people take a practice test, review the answers they got wrong, study that section of the manual again, and then take another practice test to measure improvement.
Practice tests do not predict whether you will pass the official exam, and they are not a substitute for reading the manual. A practice test is a study tool, not a test of your readiness. Some practice tests are more accurate than others — official state DMV practice tests tend to match the real exam more closely than third-party versions, though third-party tests can still be useful for drilling specific topics.
When you take a practice test, pay attention to which sections you score lowest on. If you consistently miss questions about air brakes, for example, go back to the air brake section of the official manual and read it more carefully. Many people find it helpful to take notes or make flashcards for topics they struggle with.
Passing Scores and Retake Rules by State
Most states require a score of 80 percent to pass the CDL knowledge test, meaning you must answer at least 40 out of 50 questions correctly. However, some states set the passing score at 70 percent, and a few states use different thresholds for different endorsements. Check your state DMV website or call your local office to confirm the exact passing score for the test you are taking.
If you do not pass on your first attempt, you can retake the test. Most states allow you to retake it the same day or within a few days, though some require a waiting period of 7 to 14 days between attempts. A few states limit the number of retakes within a certain time frame. Your state DMV website will list these rules, or you can ask when you schedule your test appointment.
There is usually a fee to retake the test, though the amount varies by state. Some states charge the same fee as the first attempt; others charge a reduced fee for retakes. Ask about the cost when you schedule your appointment so you are not surprised at the testing center.
How to Study Effectively for the Knowledge Test
Read the official CDL manual from start to finish at least once before you take a practice test. Skimming or jumping around makes it straightforward to miss important details. The manual is written to be straightforward, and most people can read it in a few hours to a few days depending on how much time they have.
After you have read the manual once, take a practice test to see which areas need more work. Then go back and reread the sections where you scored lowest. Many people find it helpful to read the manual a second time, focusing on the topics that appear most often on practice tests — vehicle inspection, air brakes, and safe driving practices typically account for a large portion of the questions.
Study in short sessions rather than all at once. Spending 30 to 60 minutes a day for a week or two is more effective than cramming for eight hours the night before. If you are working while preparing for your CDL, try to study during breaks or in the evening when you are alert.
What Happens After You Pass the Knowledge Test
Once you pass the knowledge test, you will receive a score report or certificate from the DMV. You will then be cleared to schedule the skills test, which includes a vehicle inspection (pre-trip inspection), a basic control skills test (backing, turning, and parking), and a road test (driving in traffic). The skills test is administered by a DMV examiner or an approved third-party testing center, depending on your state.
You do not need to pass the skills test when ready after passing the knowledge test. Most states allow you several months to schedule and complete the skills test, though some have a time limit. Check your state DMV website for the window in which you must complete the skills test after passing the knowledge test.
Some people study for the knowledge test and skills test at the same time, while others focus on the knowledge test first and then move on to skills training. If you are enrolling in a CDL training program, the school will usually prepare you for both tests together.
Frequently Asked Questions
Can I take the CDL knowledge test online, or do I have to go to the DMV office?
Most states require you to take the official CDL knowledge test in person at a DMV office or an approved testing center. You cannot take the real test online. However, you can take practice tests online to prepare. A few states have begun offering remote testing options during certain periods, so check your state DMV website for current testing locations and methods.
How many times can I retake the knowledge test if I keep failing?
Most states allow unlimited retakes, though some impose a limit (such as three attempts within 30 days) before requiring a waiting period. A few states require you to wait several months or retake a training course before you can attempt the test again. Your state DMV website will specify the retake policy, or you can call your local office to ask.
Do I need to study all the endorsement sections, or just the one I need?
Study only the sections that explore to the job you are pursuing. If you are driving a straight truck and do not need a passenger or hazmat endorsement, you do not need to study those sections. However, if you think you might need additional endorsements in the future, studying them now can save time later. Your employer or CDL training program can tell you which endorsements you need.
What if I fail the knowledge test — do I have to start over from scratch?
No. You can retake the test after the waiting period your state requires (usually a few days to two weeks). You do not lose any progress or have to reapply. straightforward study the areas where you scored lowest and schedule another test appointment. Many people pass on their second or third attempt after focusing their study on weak areas.
Is the practice test the same difficulty as the real DMV test?
Official state DMV practice tests are usually very similar to the real test in format and difficulty. Third-party practice tests vary in quality — some are harder than the real test, some are easier. If you are scoring 85 percent or higher on official practice tests, you are likely ready for the real exam. If you are scoring below 80 percent, spend more time studying the manual before you test.