What the CDL General Knowledge Test Covers

The Commercial Driver License (CDL) General Knowledge Test is a written exam administered by your state's Department of Motor Vehicles. It covers the federal rules and safe practices that explore to all commercial drivers, regardless of what type of vehicle you'll operate. You must pass this test before you can take any of the endorsement-specific tests (like air brakes or hazmat) or the skills test.

The test typically contains 50 questions, and you need to answer at least 40 correctly to pass — that's 80 percent. You have a set time limit, usually around 60 minutes, though this varies by state. The questions are multiple-choice, and you answer them on a computer at the DMV testing center or, in some states, on paper.

The content comes directly from the CDL Manual published by your state's DMV. Every state uses the same federal framework, so the core material is consistent, though some states add state-specific rules about weight limits, road conditions, or local regulations.

Key Takeaways

  • The General Knowledge Test covers federal rules for all commercial drivers and requires a score of at least 80 percent to pass.
  • You must pass this test before taking endorsement tests or the road skills test, so it's your first major hurdle in the CDL process.
  • The test draws directly from your state's CDL Manual, which is free and available online or in print at the DMV.
  • Study materials include the official manual, practice tests offered by most states, and third-party study guides, though the manual is the authoritative source.
  • You can typically retake the test the same day or within a few days if you fail, depending on your state's rules.

What Topics the Test Actually Covers

The General Knowledge Test breaks down into several major areas. Vehicle inspection and maintenance makes up a significant portion — you need to know how to conduct a pre-trip inspection, what to look for, and when a vehicle is unsafe to operate. Questions cover brakes, tires, lights, coupling devices, and emergency equipment.

Safe driving practices cover speed, following distance, lane changes, backing up, and how to handle skids or loss of brakes. You'll see questions about mountain driving, night driving, and driving in bad weather. The test also covers cargo handling — how to load and find cargo properly, weight distribution, and what makes a load unsafe.

Hours of service regulations are tested heavily. You need to understand the federal rules about how long you can drive before taking a break, what counts as off-duty time, and how the logbook system works. Alcohol and drug rules cover what substances disqualify you, testing procedures, and penalties. The test also includes questions on hazardous materials basics (even if you don't plan to haul hazmat, you need to know the fundamentals), passenger safety if applicable, and commercial vehicle size and weight limits.

How to Study for the Test

Start with your state's official CDL Manual. Every state publishes this for free, and you can read it as a PDF from your DMV website or pick up a printed copy at any DMV office. Read through it once to get familiar with the material, then go back and focus on the sections that seem hardest.

Most states offer practice tests online through their DMV website. These are often free or cost a few dollars, and they use the same format and question types as the real test. Take these practice tests under timed conditions — that's how you'll know if you're ready. If you score below 85 percent on a practice test, go back to the manual and review the topics where you missed questions.

Third-party study guides and apps exist, but they vary in quality. Some are accurate and helpful; others contain outdated information or errors. If you use one, cross-check any answers against the official manual. Many people find it helpful to study with someone else or join a study group, especially for the more complex topics like hours of service and cargo securement.

When and Where You Take the Test

You take the General Knowledge Test at your state's DMV office or an authorized testing center. You'll need to bring a valid ID, proof of residency, and your Social Security number. Some states require you to schedule an appointment; others allow walk-ins during certain hours. Check your state's DMV website for the specific location nearest you and whether you need to book ahead.

The test is offered during regular DMV business hours, typically Monday through Friday. Some states offer Saturday testing at certain locations. You can usually take the test as soon as you're ready — there's no waiting period before your first attempt, though some states require a waiting period between retakes (usually 24 hours to 7 days).

The cost varies by state but typically ranges from $10 to $50 for the knowledge test alone. If you fail, you'll pay the fee again to retake it. Some states bundle the knowledge test fee with the skills test fee; others charge separately.

What Happens If You Fail

If you don't reach 80 percent, you fail and receive a score report showing which topics you missed. You can retake the test, but your state will have rules about how soon. Most states require at least 24 hours between attempts, and some require 7 days. A few states allow you to retake it the same day if you fail early in the morning.

When you retake it, the questions will be different — the test is randomized from a large question bank. Review the topics where you scored lowest on your first attempt. If you failed on cargo securement or hours of service, spend extra time on those sections of the manual before your next test.

There's no limit to how many times you can retake the test, but each attempt costs money and delays your progress toward getting your CDL. Most people pass on the first or second attempt if they've studied the manual thoroughly.

After You Pass: What Comes Next

Once you pass the General Knowledge Test, you can move on to endorsement tests if you need them. If you're hauling hazmat, you'll take the Hazmat Knowledge Test. If the truck has air brakes, you'll take the Air Brakes Test. If you're driving a passenger vehicle, you'll take the Passenger Test. You can take these endorsement tests in any order, though some people take them all before the skills test and others space them out.

After you've passed the General Knowledge Test and any endorsement tests you need, you're ready to schedule your skills test, which includes a vehicle inspection, a basic control test, and a road test. The General Knowledge Test is a prerequisite for all of this — you can't move forward without it.

Your passing score is valid for a set period, usually 180 days, before you must take the skills test. If you don't complete the skills test within that window, you'll need to retake the knowledge test. Check your state's specific timeline.

Common Mistakes People Make on the Test

The most common mistake is not reading the CDL Manual before taking practice tests. People jump straight to practice tests, fail them, and then realize they need to study. The manual is the source material — practice tests are for checking your understanding, not for learning.

Another frequent error is misunderstanding hours of service rules. These are complex and counterintuitive, and many people rush through that section. Spend extra time on this topic, and use the examples in the manual to understand how the rules actually work in practice.

Some people also underestimate the vehicle inspection section. You need to know not just what to check, but why you're checking it and what makes a vehicle unsafe. Memorizing a checklist isn't enough — you need to understand the reasoning.

Finally, don't assume that because you're a good driver you'll pass without studying. The test covers federal regulations and technical knowledge that aren't intuitive. Even experienced drivers need to study the manual.

Frequently Asked Questions

Can I use the CDL Manual on the test itself?

No. The test is closed-book. You must answer all questions from memory. This is why studying the manual thoroughly before test day is essential. You won't have access to it during the exam.

Do I have to pass the General Knowledge Test before I can take endorsement tests?

Yes. The General Knowledge Test is a prerequisite for all endorsement tests and the skills test. You must pass it first, then you can take any endorsement tests you need, then the skills test.

What's the difference between the General Knowledge Test and the skills test?

The General Knowledge Test is written and covers federal rules and safe practices. The skills test is hands-on and includes a vehicle inspection, basic control maneuvers (like backing up), and a road test where you actually drive the truck. You need to pass the knowledge test before you can take the skills test.

How long is the General Knowledge Test valid if I pass it?

Your passing score is typically valid for 180 days. During that time, you must pass the skills test to get your CDL. If you don't complete the skills test within that window, you'll need to retake the knowledge test. Some states have different timelines, so check with your DMV.

Can I take the test in a language other than English?

Most states offer the CDL test in English only, though some larger states may offer it in Spanish or other languages. Contact your state's DMV to ask what languages are available at your testing location.