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Free CDL practice · Motion

CDL practice questions, and why the air brake section is not just a section

CDL knowledge tests are written by your state, but federal rule fixes the standard: you must correctly answer at least 80 percent of each test, across 20 required areas of knowledge. You must be 18 to hold a commercial learner’s permit and 21 to drive in interstate commerce. Our free bank runs 5,471 questions across eight areas.

Formally the Commercial Driver’s License knowledge tests. Awarding body: Federal Motor Carrier Safety Administration, with tests administered by state licensing agencies. Neuron Trainer is an independent study app and is not affiliated with, endorsed by or sponsored by the organization that owns this exam.

Get the CDL app free Jump to the practice questions

CDL at a glance, with the source for every line

Every row below is quoted from a document published by FMCSA and carries the date we checked it. Where FMCSA publishes nothing, the row says so instead of quoting a number from somewhere else.

Passing score
A driver applicant must correctly answer at least 80 percent of the questions on each knowledge testSource: 49 CFR 383.135(a)(1), Passing knowledge and skills tests, verified 7 August 2026
If you fail air brakes
An applicant who fails the air brake portion (scores less than 80 percent correct) has an air brake restriction added to the CLP or CDLSource: 49 CFR 383.135(a)(2), verified 7 August 2026
If you fail combination vehicles
An applicant who fails the combination vehicle portion must not be issued a Group A CLP or CDLSource: 49 CFR 383.135(a)(3), verified 7 August 2026
Minimum age, permit
18 years of age or older to hold a commercial learner’s permitSource: 49 CFR 383.71(a)(1), Driver application and certification procedures, verified 7 August 2026
Minimum age, interstate
At least 21 years old to be qualified to drive a commercial motor vehicle in interstate commerceSource: 49 CFR 391.11(b)(1), General qualifications of drivers, verified 7 August 2026
Permit waiting period
A CLP holder is not eligible to take the CDL skills test in the first 14 days after initial issuance of the CLPSource: 49 CFR 383.25(e), Commercial learner’s permit, verified 7 August 2026
Training prerequisite
Beginning 7 February 2022, entry-level driver training must be completed before taking the skills test for a Class A or B CDLSource: 49 CFR 383.71(a)(10) and 49 CFR 380.603, Entry-Level Driver Training applicability, verified 7 August 2026
Required knowledge
20 general areas that all commercial motor vehicle operators must have knowledge ofSource: 49 CFR 383.111(a), Required knowledge, verified 7 August 2026
Questions
Not published by FMCSA. Federal rule fixes the 80 percent pass mark and the required knowledge areas but not the number of questions. Your state licensing agency writes the test, so the count you sit depends on where you apply.Checked against: 49 CFR part 383, subparts G and H, verified 7 August 2026
Time limit
Not published by FMCSA. No federal time limit exists for the CDL knowledge tests. Part 383 sets content and scoring standards only, and the time allowed is set by your state.Checked against: 49 CFR part 383, subparts G and H, verified 7 August 2026
Cost
Not published by FMCSA. The FMCSA does not set CDL testing or licensing fees. They are charged by your state licensing agency and vary widely between states.Checked against: 49 CFR part 383, verified 7 August 2026
How long a CDL lasts
Not published by FMCSA. 49 CFR 383.73 governs how a State issues a CDL and caps the commercial learner’s permit at one year, but sets no term for how long a CDL itself stays valid.Checked against: eCFR, 49 CFR 383.73, verified 7 August 2026

Check your state: the FMCSA sets the 80 percent standard and the required knowledge areas, but question counts, time limits and fees come from your state licensing agency, so confirm those before you book.

What our CDL question bank covers

What this app's question bank covers — our own category shares across 5,471 questions, not FMCSA's published blueprint.
CategoryQuestions in our bankShare of our bank
General Knowledge
Fundamental CDL concepts and regulations
94317.2%
HazMat
Hazardous materials transportation regulations
65011.9%
Air Brakes
Air brake systems and safety procedures
64111.7%
Combination Vehicles
Tractor-trailer and combination vehicle operation
64711.8%
School Bus
School bus operation and student safety
64711.8%
Passenger
Passenger vehicle operation and safety
64511.8%
Doubles & Triples
Multiple trailer vehicle operation
65011.9%
Tanker
Liquid cargo transportation safety
64811.8%

Scroll the table sideways to see every column.

Try it

5 questions from our CDL bank

Five questions drawn straight from the shipped bank, covering general knowledge, air brakes, combination vehicles, tankers and school buses.

CDL · Free practice Every answer explained. No signup, no email wall.

  1. Question 1 of 5

    If your drive wheels begin to spin when starting from a stop, what should you do?
    Answer and explanation

    Correct answer: Take your foot off the accelerator to regain traction

    If your drive wheels start to spin on a slick surface when you are accelerating from a stop, you should ease off the accelerator. Reducing power helps the tires regain traction. Spinning the wheels faster will only make traction worse.

  2. Question 2 of 5

    A driver is performing a pre-trip inspection on a vehicle equipped with air brakes. At what PSI should the low air pressure warning device activate?
    Answer and explanation

    Correct answer: Before air pressure drops below 60 PSI

    The low air pressure warning device must activate before air pressure drops below 60 PSI, as required by federal regulations. This early warning gives the driver time to safely stop before brake performance is compromised. 80 PSI is close but too high for the warning threshold. 100 PSI is the minimum pressure at which you should apply brakes after building air. 120 PSI is typically near the governor cut-out pressure, far too high for a low-pressure warning.

  3. Question 3 of 5

    During a pre-trip inspection of a combination vehicle, the driver finds the fifth wheel locking jaws are around the shank, not the head of the kingpin. The driver should:
    Answer and explanation

    Correct answer: Not operate the vehicle until the coupling is corrected

    When the fifth wheel locking jaws are around the shank instead of the head of the kingpin, the coupling is unsafe and can separate during operation, causing a catastrophic accident. The jaws must be securely locked around the head (the wider portion) of the kingpin to provide a safe connection. Driving slowly does not make an unsafe coupling safe; the appearance of security is irrelevant when the mechanical engagement is incorrect; and adding grease addresses friction, not the fundamental coupling failure. This defect must be corrected before any operation, as trailer separation is one of the most dangerous combination vehicle failures.

  4. Question 4 of 5

    What is the purpose of baffles inside a tank trailer?
    Answer and explanation

    Correct answer: To reduce the surge effect of liquid cargo

    Baffles are internal walls with holes that slow down the movement of liquid cargo, thereby reducing the surge effect during acceleration, braking, and turning. This makes the vehicle more stable and easier to control. Baffles do not separate different cargo types (that's the purpose of separate compartments with bulkheads), do not increase capacity (they actually slightly reduce usable space), and while they may incidentally affect cleaning, that is not their primary safety purpose. The key function is surge control.

  5. Question 5 of 5

    Which area represents the most dangerous zone around a school bus where children are most at risk of not being seen by the driver?
    Answer and explanation

    Correct answer: The area directly in front of the bus extending 10 feet

    The most dangerous zone is directly in front of the bus, extending approximately 10 feet from the front bumper, where the driver has virtually no visibility of small children. This area is considered the highest-risk danger zone because children who drop items or step in front of the bus completely disappear from the driver's view. While the right side mirror has a blind spot, it is less critical than the front zone due to crossover mirror coverage. The area behind the bus is dangerous but typically involves backing situations rather than loading/unloading. The left side has better visibility due to the driver's seating position. Drivers must always account for this front danger zone by waiting for children to move to the side door area before proceeding.

What actually trips people up

Air brakes, because failing it is not neutral

Score under 80 percent on the air brake portion and an air brake restriction goes onto your CLP or CDL. You do not simply lose a section, you lose the ability to drive an air-braked vehicle until you pass both the air brake knowledge test and the air brake pre-trip inspection. The number worth committing to memory: the low air pressure warning must activate before pressure drops below 60 psi.

The combination vehicle portion is a gate

Fail it and you must not be issued a Group A CLP or CDL at all. Off-tracking, crack-the-whip and fifth-wheel coupling questions are worth more of your evening than they look, because this section does not just cost you marks, it costs you the class of license.

Endorsements are separate tests, each at 80 percent

HazMat, Passenger, School Bus, Tanker and Doubles or Triples all have their own knowledge test. People book the general knowledge test, pass it, and then discover the job they wanted needs two more sittings.

The scheduling traps that have nothing to do with knowledge

You are not eligible to take the skills test in the first 14 days after your CLP is issued, and since 7 February 2022 you must finish entry-level driver training before the skills test for a Class A or B CDL. Both catch people who studied perfectly and booked too early.

Two different age rules

You need to be 18 to hold a commercial learner’s permit, and 21 to be qualified to drive a commercial motor vehicle in interstate commerce. Plenty of drivers under 21 hold a valid CDL and cannot legally cross a state line with it.

How long should I study for the CDL knowledge tests?

Four weeks, because there is genuinely more material here than in any other test on this site.

Week 1: General Knowledge

The largest single area and the base for everything else. Run a Smart Quiz to find your weak categories, then drill vehicle control, space management and hours-of-service basics until you are clearing 85 percent.

Week 2: Air Brakes and Pre-Trip

Air brakes first, because the restriction stays on your license until you retest. Then the combination vehicle material, because failing that portion means no Group A license at all. Our bank does not carve pre-trip inspection out as its own category, so take that from your state manual.

Week 3: Your endorsements

Pick only the ones your job needs. HazMat and Doubles and Triples carry 650 questions each in our bank, and Tanker 648, so there is plenty to drill without repeating yourself.

Week 4: Simulate and book

Full timed runs on each test you plan to sit. Check your CLP paperwork and your entry-level driver training record while you drill, because the 14-day clock starts the day the permit is issued, not the day you feel ready. Call your state licensing agency before you book rather than after: it sets the question count, the time allowed and the fee, and none of those three numbers is fixed federally. Ask what happens if you fail one endorsement test on a day you pass the others, because the answer varies and it changes how many trips you make.

Is the CDL knowledge test hard?

It is a volume problem more than a difficulty problem. Federal rule requires knowledge of twenty general areas, and depending on your endorsements you may sit up to six separate tests, every one of them held to the same 80 percent bar.

The federal rules do not set a question count or a time limit, so what you actually sit varies by state. That is the most common surprise on test day, and it is why there is no national question count printed anywhere on this page.

Our own bank splits by difficulty as 677, 1,605, 1,736 and 1,453 across four levels, so nearly six in ten sits above the midpoint. That is our number from our bank, and it is the only difficulty claim here.

How the CDL differs from the exams beside it

Every other test on this site is one exam that gets you one license. The CDL is a stack: a general knowledge test, a separate air brake test, a combination vehicle test, and an endorsement test for each thing you want to haul, all held to the same 80 percent bar. It is also the only one here with a skills test behind it, a mandatory training rule in front of it, and a license that is a job requirement rather than permission to drive your own car.

Questions people actually ask about the CDL

What score do you need to pass the CDL knowledge test?

At least 80 percent correct on each test. This is a federal standard in 49 CFR 383.135, so it is the same in every state, for the general knowledge test and for every endorsement test.

How many questions are on the CDL general knowledge test?

Federal rule does not set a number. Your state licensing agency writes the test and decides how long it is, so the count you sit depends on where you apply.

What happens if I fail the air brake section?

An air brake restriction goes onto your CLP or CDL, which means you cannot drive a vehicle with air brakes. It comes off only when you pass the air brake knowledge test and the air brake pre-trip inspection.

How old do I have to be to get a CDL?

You must be 18 or older to hold a commercial learner’s permit. To be qualified to drive a commercial motor vehicle in interstate commerce, federal rule requires you to be at least 21.

How long after getting my CLP can I take the skills test?

Not in the first 14 days. Federal rule makes a CLP holder ineligible for the CDL skills test for 14 days after the permit is first issued.

Do I need entry-level driver training first?

If you got your CLP on or after 7 February 2022, yes. You must complete the training in 49 CFR part 380 subpart F before taking the skills test for a Class A or B CDL.

How many endorsement tests will I need?

One for each endorsement, and each is a separate 80 percent hurdle. HazMat, Passenger, School Bus, Tanker and Doubles or Triples are the common ones. Take only what the job actually asks for.

Are these real questions from the state CDL test?

No. State exam banks are not public and copying them would be theft. These are original questions written to the federal knowledge requirements in 49 CFR 383.111 and the state CDL manuals.

Practice another Motion exam

Driving & aviation. Every one of these pages is built the same way: sourced facts, an honest admission where the sponsor publishes nothing, and free practice questions.

The app

Practice the CDL in the app

CDL Test Prep 2026 went live on the App Store on 7 August 2026, free to download. It has no ratings yet, so there is no star average to show you. The bank is 5,471 questions, the largest in the portfolio: General Knowledge 943 · HazMat 650 · Doubles and Triples 650 · Tanker 648 · Combination Vehicles 647 · School Bus 647 · Passenger 645 · Air Brakes 641. Every question carries a full explanation, and the Exam Simulator runs 50 questions in 120 minutes. Straight about the balance: General Knowledge is nearly half again the size of any other single category, and the endorsements sit within a few questions of each other, so the app cannot tell you which ones your state weights hardest. Pair it with your own state’s CDL manual and, for the pre-trip inspection, an actual walk around the vehicle.

  • Smart Quiz — keeps returning to the categories you keep missing
  • Topic Drill — one category at a time, on its own
  • Exam Simulator — a fixed-length timed paper (50 questions in 120 minutes, as this app sets it). It does not get harder as you go; the length and the mix are fixed.
  • AI tutor — re-explains any question in plain English
  • Progress tracking, reported per category
  • Study reminders
  • Light and dark themes

The app calls you ready at 80% on its own simulator. That is an in-app practice target we chose, not FMCSA's passing standard.

Get CDL Test Prep 2026 free on the App Store

Listed on the App Store as CDL Test Prep 2026. Free to download; Premium unlocks the full bank and unlimited tutor explanations.

Eight areas. One app. Free to start.

5,471 questions with an explanation on every one, covering the general knowledge test and every endorsement, plus a 50-question timed simulator and an AI tutor for the times a written explanation is not enough.

Download free on the App Store

Sources, and when we last checked them

This page was last reviewed on . The 8 facts quoted above were last checked against their sources on . Where FMCSA publishes nothing, the table above says so rather than guessing.

CDL standards are set by the Federal Motor Carrier Safety Administration and the tests are administered by state driver licensing agencies. Neuron Trainer is an independent study resource and is not affiliated with, endorsed by or sponsored by the FMCSA or any state agency.