The CDL written test is the multiple-choice knowledge exam you have to pass before your state will issue a Commercial Learner’s Permit, the first step toward a full Commercial Driver’s License. You need at least 80% on every section you take, and depending on the class of CDL you want and any endorsements you plan to add, you may sit for several separate knowledge tests in one visit.1eCFR. 49 CFR Part 383 Subpart H – Tests The exam is computer-based in most states, and the questions come from federal standards, though each state writes and administers its own version.
What the General Knowledge Test Covers
Every CDL applicant, regardless of vehicle class, takes the General Knowledge test. It typically runs about 50 questions on the foundational rules of commercial driving: safe driving techniques like managing speed and following distance, pre-trip and post-trip vehicle inspections, basic vehicle control such as shifting and backing, cargo securement and weight distribution, and federal regulations including hours-of-service and drug and alcohol policies.
Most questions ask for practical judgment. What to do when your brakes fade on a downhill grade. How to check tire pressure during an inspection. How much space to leave between your vehicle and the one ahead at highway speed. You also need to know specific numbers, though: stopping distances, weight limits, required inspection intervals. The state CDL manual spells all of them out.
Which Tests You Actually Have to Take
Which written tests apply to you depends on the CDL class you need and whether you’ll haul specialized cargo or carry passengers. Federal regulations define three CDL classes by vehicle weight:
- Class A covers vehicle combinations with a gross combined weight rating over 26,001 pounds where the towed vehicle weighs more than 10,000 pounds. Tractor-trailers and most big rigs fall here.
- Class B covers single vehicles with a gross vehicle weight rating over 26,000 pounds, or any such vehicle towing something under 10,000 pounds. Dump trucks, large buses, and delivery trucks fall here.
- Class C covers vehicles that don’t hit the Class A or B weight thresholds but carry hazardous materials or are designed for 16 or more people including the driver.2Federal Motor Carrier Safety Administration. Passenger Carrier Guidance Fact Sheet
Class A applicants pass both the General Knowledge test and the Combination Vehicles test. Class B applicants take General Knowledge alone unless they need endorsements. Class C applicants take General Knowledge plus the endorsement knowledge test for whatever specialized operation they’ll perform.
Endorsement Knowledge Tests
Endorsements authorize you to operate specific types of commercial vehicles or haul certain cargo, and each one requires its own written test on top of General Knowledge:
- Air Brakes, required if your vehicle uses air brakes. Failing or skipping this test places an air brake restriction on your CDL.
- Hazardous Materials (H), required to haul hazardous cargo. This endorsement also requires a security threat assessment through TSA, and processing can take 45 days or longer.3Transportation Security Administration. HAZMAT Endorsement
- Tanker (N), required to drive tank vehicles carrying liquid or gaseous cargo.
- Passenger (P), required for vehicles designed to carry 16 or more people including the driver.2Federal Motor Carrier Safety Administration. Passenger Carrier Guidance Fact Sheet
- School Bus (S), required for school bus operations in addition to the Passenger endorsement.
- Doubles/Triples (T), required to pull two or three trailers.
You can combine endorsements on one CDL. A driver hauling liquid hazardous materials, for instance, needs both Tanker and HazMat, and takes both written tests.
One training rule attaches to the written test specifically: if you’re seeking a HazMat endorsement for the first time, you must complete Entry-Level Driver Training theory instruction through a provider on FMCSA’s Training Provider Registry before the state will let you sit for the HazMat knowledge test.4eCFR. 49 CFR Part 380 Subpart F – Entry-Level Driver Training Requirements Your provider submits your completion record to the federal registry, and your state agency checks it before allowing you to test.5FMCSA Training Provider Registry. Training Provider Registry If the record hasn’t been uploaded, you’ll be turned away, so confirm it’s been reported before scheduling. Drivers who held the relevant endorsement before February 7, 2022, are grandfathered, and veterans with military commercial vehicle experience may qualify for a waiver.
How to Prepare
Your state’s official CDL manual is the single most important study resource. Every question on the test comes from the material in that manual, and most states offer it as a free download from their licensing agency website. If you only use one resource, make it this one.
Online practice tests are genuinely useful, not as a substitute for reading the manual but as a way to find out what you don’t actually know yet. Most people discover they’re weaker on specific numbers (stopping distances, inspection intervals, weight limits) than on the conceptual material. Taking practice tests before you feel ready is the point; they show you where to focus.
A few study habits make a real difference. Break the manual into sections and work one topic per session rather than trying to absorb everything at once. Pay special attention to the air brakes section if you need that endorsement, because it has the highest failure rate among endorsement tests. The material is technical and unfamiliar to most new drivers. Write down every number you need to memorize: following distance formulas, maximum air pressure loss rates, minimum tread depths. Those are the questions people miss.
Some CDL training programs include dedicated test preparation modules alongside behind-the-wheel instruction. If you’re enrolled in a program listed on the Training Provider Registry, the theory portion of your course will overlap heavily with the written test content.
Test Day
CDL knowledge tests are administered at state DMV offices or authorized licensing centers. Bring valid photo identification, proof of residency or domicile, proof of citizenship or lawful permanent residency, and your Social Security card or documentation of your Social Security number.6eCFR. 49 CFR 383.71 – CLP Application Requirements If your self-certification category requires a medical examiner’s certificate, bring that too. Missing a single document can mean a wasted trip.
Expect to pay application and testing fees. These vary by state, generally ranging from around $10 to $100 depending on the state and how many endorsement tests you take. Some states charge a flat CLP fee that covers all knowledge tests; others charge per section.
The testing environment is straightforward. You’ll sit at a computer terminal and answer multiple-choice questions. Electronic devices, notes, and study materials are not allowed in the testing area. Each section is scored independently, and you need at least 80% on each one to pass.1eCFR. 49 CFR Part 383 Subpart H – Tests If you pass some sections and fail others, most states let you keep the ones you passed and retake only what you missed.
Under current federal law, the knowledge test can be administered in languages other than English. Only the skills test is required to be in English. Availability of non-English testing varies by state, so check with your local licensing agency in advance if you need a translation.
If You Fail a Section
Failing a section is not unusual, and it isn’t the end of the process. Most states allow you to retake a failed section after a short waiting period, often the next business day. Retake policies, including waiting periods, fees, and limits on the number of attempts, vary by state. Some states allow unlimited retakes within a set timeframe, while others require you to wait weeks or reapply after a certain number of failures.
Resist the urge to rebook and retake the same test immediately without more study. Questions are drawn from a pool, so you won’t see the exact same exam, but the weak areas that tripped you up will still be there. Go back to the manual, focus on the topics where you struggled, and take practice tests until you’re consistently scoring above 90% before trying again. The $10 or $20 retake fee adds up, and repeated failures push back the day you actually get behind the wheel.
What Passing Gets You
Passing all required knowledge tests earns you a Commercial Learner’s Permit. The CLP lets you practice driving a commercial vehicle on public roads, but only under direct supervision: a licensed CDL holder with the correct class and endorsements must be physically present in the front seat next to you at all times.7eCFR. 49 CFR 383.25 – Commercial Learner’s Permit (CLP)
The CLP comes with restrictions and a tight clock. You cannot take the CDL skills (road) test until at least 14 days after the CLP was issued.7eCFR. 49 CFR 383.25 – Commercial Learner’s Permit (CLP) The permit is valid for no more than one year from its issue date, and if it expires before you pass the skills test, you’ll need to retake the knowledge tests to get a new one.8Federal Register. Commercial Learner’s Permit Validity Don’t let it sit unused for months.
CLP holders with a Passenger or School Bus endorsement cannot carry actual passengers during training, only examiners, inspectors, other trainees, and the supervising CDL holder. A CLP holder with a Tanker endorsement may only operate an empty tank vehicle. HazMat endorsements are not permitted on a CLP at all.7eCFR. 49 CFR 383.25 – Commercial Learner’s Permit (CLP)