The CDL written test covers vehicle control, safety rules, and hazard recognition specific to commercial trucks

The Commercial Driver's License (CDL) written test is not one exam — it's a series of tests, each covering a different endorsement or vehicle class. Every CDL applicant takes the General Knowledge test, which covers federal trucking regulations, vehicle inspection, and safe driving practices. Depending on what you plan to drive, you'll also take tests for Passenger (P), Tanker (N), Hazardous Materials (H), or other endorsements. Each test is separate, and you can pass some and fail others.

The General Knowledge test typically has 50 questions, and you need to answer at least 40 correctly to pass — that's 80 percent. Endorsement tests are shorter, usually 20 to 30 questions, with the same 80 percent passing threshold. You take these tests at your state's Department of Motor Vehicles (DMV) or an approved testing location. Most states let you retake a failed test after a waiting period, usually 7 to 14 days.

Key Takeaways

  • The General Knowledge test covers 50 questions on vehicle inspection, braking systems, cargo security, and federal safety rules, with an 80 percent passing score required.
  • Endorsement tests (Hazmat, Tanker, Passenger, or others) are separate exams you take only if your job requires them, each with its own 80 percent threshold.
  • Questions are multiple-choice with four answer options, and you answer them on a computer or paper depending on your state's testing system.
  • Most states allow you to retake a failed test after 7 to 14 days, but some charge a retest fee each time you take the exam.

What the General Knowledge test covers

The General Knowledge test focuses on the rules and mechanics of operating a commercial vehicle safely. You'll see questions about pre-trip vehicle inspection — checking your brakes, lights, tires, mirrors, and coupling devices before you drive. The test asks you to identify what makes a vehicle unsafe and what you should do if you find a problem. You need to know the difference between service brakes and parking brakes, and how to recognize brake failure.

The test also covers cargo security and weight distribution. You'll answer questions about how to load a truck safely, what happens when cargo shifts, and how overweight vehicles affect braking and handling. Federal Hours of Service rules appear on nearly every test — how long you can drive before you must rest, how to log your time, and what happens if you violate these rules. You'll also see questions on hazardous materials basics, even if you don't plan to haul hazmat, because all CDL holders need to know the fundamentals.

Road safety and hazard recognition make up a large portion of the test. Questions ask you to identify dangerous situations — a car merging into your lane, a child running into the road, a vehicle with brake lights out ahead of you — and choose the safest response. You need to know how to handle skids, what to do if your brakes fail on a downhill grade, and how to drive safely in rain or fog. The test also covers passenger safety if you're driving a bus, including evacuation procedures and how to handle disruptive passengers.

Endorsement tests and what they ask

If your job requires you to haul passengers, tanker cargo, or hazardous materials, you'll take an endorsement test in addition to General Knowledge. The Passenger (P) endorsement test covers bus operation, passenger safety, and emergency procedures. You'll answer questions about seating arrangements, how to help elderly or disabled passengers, and what to do if a passenger becomes ill or violent. The test also covers evacuation routes and how to use emergency exits.

The Tanker (N) endorsement test focuses on the unique challenges of hauling liquids. Questions cover how liquid shifts inside a tank during braking and turning, why tanker vehicles are harder to control than box trucks, and how to inspect a tanker before driving. You'll learn about surge and slosh — the movement of liquid that can cause the truck to tip or jackknife — and how to drive differently to prevent it.

The Hazardous Materials (H) endorsement test is often the most detailed. It covers how to identify hazmat shipments, what the placard system means, how to load and find hazmat cargo, and what to do if there's a spill or accident. You'll answer questions about which materials can be loaded together, how to communicate hazmat information to emergency responders, and what paperwork you need to carry. This test is required if you haul any hazardous cargo, even small quantities.

Question format and how to prepare

All CDL test questions are multiple-choice with four answer options. You select one answer per question. Most states now use computer-based testing, where you read the question on a screen and click your answer. Some states still offer paper tests, though these are becoming less common. The computer system shows you one question at a time and doesn't let you go back to change an earlier answer, so you need to read carefully before you select.

The best preparation is to study the CDL manual for your state — every state publishes one free on its DMV website. The manual contains the exact rules and scenarios the test covers. Many people also use practice tests, which are available online and through CDL training schools. Practice tests follow the same format as the real exam and help you get used to the question style and time pressure. Some practice tests are free; others charge a small fee.

Study groups and CDL training schools offer classroom instruction, but you can also prepare on your own by reading the manual and taking practice tests repeatedly until you score 85 to 90 percent consistently. The test itself is not timed — you can take as long as you need to answer each question — so rushing is not the problem. The problem is usually not knowing the material well enough, so focus your study time on the areas where your practice test scores are lowest.

Common topics that trip up test-takers

Hours of Service rules confuse many applicants because the rules have specific numbers and exceptions. You need to memorize that you can drive a maximum of 11 hours after 10 consecutive hours off duty, and that you must take a 30-minute break after 8 hours of driving. The rules change slightly for different types of operations, and the test asks about these variations. Read the Hours of Service section of your manual multiple times and use flashcards if numbers don't stick easily.

Braking system questions also trip up many people because the terminology is specific. You need to know the difference between the service brake (the main brake you use to slow down), the parking brake (the brake you use when parked), and the emergency brake (a backup system). The test asks what happens if the service brake fails, how to recognize brake fade, and what to do on a long downhill grade. If you don't understand how air brakes work, spend extra time on this section.

Vehicle inspection questions require you to know what to look for and in what order. The test may ask you to identify which parts you should check first, or what to do if you find a problem during inspection. You don't need to memorize every bolt, but you do need to know the major systems: tires, lights, mirrors, coupling devices, brakes, and steering. Practice describing a pre-trip inspection out loud, as if you're explaining it to someone else — this helps the information stick.

Retesting and score requirements by state

If you fail a test, your state's DMV will tell you which sections you scored lowest on. Most states require you to wait 7 to 14 days before you can retake the same test, though a few states allow when ready retesting. Each retest usually costs money — typically $10 to $50 per test — so budget for this if you think you might need more than one attempt. Some states waive the retest fee if you fail by a small margin, so ask at your testing location.

You can take the General Knowledge test and endorsement tests in any order, and you don't have to pass them all on the same day. Many people take General Knowledge first, then come back for endorsements after they've studied more. Once you pass all required tests, you'll get your CDL permit, which lets you practice driving a commercial vehicle with a licensed CDL holder in the passenger seat. After that, you'll need to pass a road test to get your full CDL license.

Frequently Asked Questions

Can I use a calculator or notes during the test?

No. You cannot bring any materials into the testing room except your ID and any documents your state requires. The test is designed to measure what you know from memory, not what you can look up. If you struggle with math, practice weight and distance calculations while you study so you're comfortable doing them in your head.

What happens if I fail the General Knowledge test?

You can retake it after your state's waiting period, usually 7 to 14 days. You'll pay the test fee again. There's no limit to how many times you can retake it, but each attempt costs money and takes time. Focus your study on the sections where you scored lowest before your next attempt.

Do I have to take all the endorsement tests, or only the ones I need?

You only take endorsement tests for the endorsements you need for your job. If you only drive a straight truck with no passengers or hazmat, you only take General Knowledge. You can add endorsements later if your job changes, so you don't have to study everything at once.

How long does the test take?

The General Knowledge test usually takes 30 to 60 minutes, depending on how much time you spend on each question. Endorsement tests are shorter, typically 15 to 30 minutes. There's no time limit, so you can take as long as you need to think through each answer.

Can I study the CDL manual online, or do I need to buy a book?

Every state publishes its CDL manual free on the DMV website, and you can read it online or read it as a PDF. You don't need to buy anything. Many people print it out or use a tablet to study, while others use free practice test websites. Paid study materials and courses can help, but they're not required.