CDL Combination Practice Test 2026 — Free
Free CDL combination practice test for 2026: 20 questions with answers on coupling, air lines and inspection — the knowledge test every Class A permit requires.
What's on the Combination Vehicles CDL test
Answering from memory beats re-reading — retrieval practice roughly doubles what you remember a week later. These free questions are modeled on the official Combination Vehicles CDL knowledge test.
- Official test
- 20
- Practice questions here
- 20
- To pass
- 16/20 correct (80%)
- Updated
- September 2026
- 100% free
CDL combination vehicles test at a glance
- What it is
- A knowledge test, not an endorsement — mandatory for every Class A (tractor-trailer) permit and license
- Test type
- Knowledge test; fail it and no Group A learner’s permit or CDL may be issued
- Who needs it
- Every Class A applicant, including Class B holders upgrading — not required for Class B or C
- Where to study
- The “Combination Vehicles” section of your state CDL manual (Section 6 in the model manual), with Section 5 (Air Brakes)
- Official test
- 20 questions under the AAMVA model most states use — your state may differ
- Pass mark
- 80% — 16 of 20 correct (federal, 49 CFR 383.135)
- This practice set
- 20 questions with explanations, free, no sign-up
Show all 20 practice questions with answers
If you are not pulling a trailer, why should you lock the truck gladhands together (or use dummy couplers)?
- To make it easier to attach to a trailer later.
- It helps balance the air pressure between the tractor and trailer.
- It will keep dirt or water out of the lines.
Correct answer: It will keep dirt or water out of the lines.
When you're not pulling a trailer, connecting the glad hands together or to dummy couplers helps keep dirt and water out of the air lines. This keeps the lines clean and ready for when you need to hook up to a trailer again.
For a coupling to be properly done, the safety latch on the fifth wheel locking lever must be _____.
- In front of the locking lever.
- Over the locking lever
- Beside the locking lever
Correct answer: Over the locking lever
The right way to hook up the fifth wheel locking lever for it to be safe and right is for the safety latch to be over the locking lever.
What is the proper position for the fifth wheel when coupling with a trailer?
- Tilted down toward the end of the trailer.
- Slanted sideways towards the driver's side
- Above the roof of the truck
Correct answer: Tilted down toward the end of the trailer.
When connecting the trailer to the truck, the fifth wheel (the part that connects them) should be tilted down towards the end of the trailer. This position helps hook up the trailer securely.
After coupling the trailer with the truck, in what position should the truck protection control valve be set?
- Horizontal position
- Normal position
- Left position
Correct answer: Normal position
After hooking up a trailer to a truck, the valve that helps control the brakes should be set to the 'normal' position. This makes sure the brakes work right when needed.
What is correct out of the following?
- The brakes work more efficiently when the road is wet.
- Braking efficiency increases as vehicle weight decreases.
- Bobtail tractors can take longer to stop than a combination vehicle loaded to maximum gross weight.
Correct answer: Bobtail tractors can take longer to stop than a combination vehicle loaded to maximum gross weight.
Bobtail tractors without a trailer can actually take longer to stop compared to when they are pulling a fully loaded trailer. This is because the weight helps push the brakes down more effectively.
Where should the truck be when you uncouple the trailer and inspect the landing gear?
- Parked at a 45-degree angle to the trailer.
- Next to the trailer, but not aligned with it.
- With the tractor frame under the trailer.
Correct answer: With the tractor frame under the trailer.
After you disconnect the trailer, park your truck straight under the trailer, not to the side or at an angle. This way, you're in the right spot to check the landing gear safely and properly.
After you hook up the air lines, but before you back up under the trailer, you should:
- Disconnect the electrical line.
- Supply air to the trailer system, then pull out the air supply knob.
- Check the tire pressure on the trailer.
Correct answer: Supply air to the trailer system, then pull out the air supply knob.
After you connect the air lines, before you move your truck under the trailer, you need to make sure the trailer's air system is working. Do this by sending air into the trailer's system and then pulling the knob that controls the air supply. This ensures the brakes and other systems are ready to safely operate.
When operating a combination vehicle, the trailer unexpectedly disconnects, causing both air lines to separate. In addition to the trailer brakes coming on, you expect:
- The emergency brakes to release.
- The tractor protection valve to close.
- The trailer lights to go out.
Correct answer: The tractor protection valve to close.
When the trailer comes off and air lines break, special valve shuts to keep air in the truck's brakes, ensuring it can still be controlled.
You're getting ready to reverse your truck under a semitrailer. The semitrailer is at the correct height when the:
- Fifth wheel is completely visible below the trailer.
- Trailer will be lifted slightly when the tractor backs under it.
- Kingpin locks into place without any adjustment needed.
Correct answer: Trailer will be lifted slightly when the tractor backs under it.
The trailer is at the right height for connecting if it slightly lifts when the tractor backs under it. This means the tractor fits just right, not too high or low, making a secure connection.
The higher the center of gravity of your truck, the:
- Less control over the brakes
- Easier to turn over.
- Harder to accelerate.
Correct answer: Easier to turn over.
When your truck's center of gravity is high, it means the truck is more likely to tip over, especially when turning. This doesn't really affect how the brakes work or how fast the truck can speed up.
Why is it necessary to put grease on the fifth wheel plate?
- To enhance tire traction.
- To prevent steering problems.
- To improve fuel efficiency.
Correct answer: To prevent steering problems.
Greasing the fifth wheel plate is crucial because it helps prevent steering problems. Without proper lubrication, the friction between the tractor and the trailer can make steering harder and less smooth. This can lead to difficulties in controlling the vehicle, especially when turning.
When uncoupling the trailer, after you turn off the trailer air supply and make sure the trailer's brakes are set, you should:
- Check the trailer's tire pressure.
- Back up gently to ease pressure on the fifth wheel.
- Check the engine oil level.
Correct answer: Back up gently to ease pressure on the fifth wheel.
After turning off the trailer's air supply and making sure its brakes are locked, you should back up a little bit. This helps reduce pressure on the connection point (fifth wheel) between your truck and the trailer, making it easier to separate them.
A truck pulling a _______ trailer needs the longest distance to stop.
- Heavy
- Slightly damaged
- Empty
Correct answer: Empty
An empty trailer requires more stopping distance because it lacks the weight that typically provides traction during braking. As a result, it takes longer to come to a complete stop compared to a heavily loaded trailer.
When you're driving behind another car in good weather, make sure there's at least one second of space for every ____ feet of your vehicle's length.
- 30
- 20
- 10
Correct answer: 10
When following another vehicle, keep at least 1 second of space for every 10 feet of your vehicle's length. This gives you enough room to stop safely if needed.
When driving a truck with two trailers, which shut-off valve do you have to close on the last trailer?
- Side valve
- Front valve.
- Back valve.
Correct answer: Back valve.
When driving a truck with two trailers, make sure to close the back valve on the last trailer. This helps keep the air pressure right so your brakes work properly.
When testing a combination vehicle, with the engine turned off and the brakes applied, the air shouldn't leak out faster than _____ psi every minute.
- 4
- 3
- 2
Correct answer: 4
For a big vehicle with multiple parts, like a truck pulling a trailer, when it's not running and the brakes are applied, the air pressure in the brakes shouldn't drop more than 4 psi in a minute. This ensures the brakes stay strong and can stop the vehicle safely.
Trailers with air brakes made before 1975:
- Are not required to have spring brakes.
- Usually need a glad hand converter.
- Cannot be legally operated on interstate highways.
Correct answer: Are not required to have spring brakes.
Trailers with air brakes made before 1975 don't need to have a special system (ABS) to stop wheels from locking when braking. They also don't have to have spring brakes, which can automatically apply brakes if there's a problem. These trailers need their brakes adjusted by hand.
For a combination vehicle that uses air brakes, when the engine is off and the brakes are off, the air brake leakage rate should not be more than ____ psi every minute.
- 1/2
- 3
- 2
Correct answer: 3
When checking if the air brakes on a big truck and trailer are leaking too much (with the engine off and not using the brakes), it's okay if the air pressure drops a little, but not more than 3 pounds per square inch (psi) every minute.
How can you stop a trailer from skidding?
- Release the brakes.
- Apply the brakes
- Tap the brakes lightly.
Correct answer: Release the brakes.
If your trailer starts to skid, quickly let go of the brakes. This helps your wheels start rolling again and gets the trailer back under control.
There are two ways a driver can stop a truck from rolling over. They are: (1) put the load as low as possible and (2):
- Keep both hands firmly on the steering wheel.
- Go slow around turns.
- Drive with windows open.
Correct answer: Go slow around turns.
To stop a truck from tipping over, do two things: 1) Load stuff low down to keep it stable. 2) Take corners slowly. This way, the truck is more balanced and less likely to fall over.
What the CDL combination vehicles test is — and who needs it
The combination vehicles test is the knowledge test that separates a Class A from a Class B CDL. It is not an endorsement — no letter is printed on the license — but federal rule makes it a hard gate: an applicant who fails the combination vehicle portion of the knowledge test must not be issued a Group A (Class A) learner’s permit or CDL.
Group A is any combination of vehicles with a gross combination weight rating of 26,001 pounds or more where the vehicle or vehicles being towed are rated over 10,000 pounds — the tractor-trailer class. That is exactly what the test is about: coupling and uncoupling a tractor and semi-trailer, inspecting a combination, and the handling and air-brake behavior that only show up when you pull a trailer.
Pulling two or three trailers is a further step — that requires the doubles/triples (T) endorsement, whose knowledge test builds on this material. And because nearly every combination vehicle is air-braked, plan on the air brakes test alongside this one: the federal combination knowledge areas explicitly include air brakes.
49 CFR 383.135(a)(3), 383.91(a)(1), 383.111(c), 383.93(b)(1)
Drivers who need to pass the combination vehicles test
Take the combination test with your permit tests if any of these describe you:
- Every first-time Class A applicant — dry van, reefer, flatbed, tank trailer, car hauler, intermodal.
- Class B or Class C holders upgrading to Class A: an upgrade requires passing all the knowledge tests for the new vehicle group.
- Drivers who will pull doubles or triples — the T endorsement test assumes you already know the combination material.
- Not required for a Class B or Class C license: the combination gate applies only to Group A.
49 CFR 383.135(a)(3), 383.71(e)(2), 383.93(b)(1)
What is on the combination vehicles knowledge test
Federal rule names three knowledge areas every combination vehicles test must cover; the model manual’s Section 6 fills them in. Expect questions on:
- Coupling and uncoupling — the step-by-step procedure for connecting a tractor to a semi-trailer and separating them safely.
- Vehicle inspection — the inspection points unique to combinations: fifth wheel and kingpin, locking jaws, landing gear, glad hands and air and electrical lines.
- Safely operating combination vehicles — rollover risk, off-tracking, trailer skids and jackknifing, turning and backing with a trailer.
- Air brakes on combinations — the trailer hand valve, tractor protection valve, trailer air supply control and what happens when the air lines are severed.
49 CFR 383.111(c)
How to pass the combination test and earn a Class A
Pass general knowledge, then combination and air brakes, for a Class A permit
A commercial learner’s permit requires a passing general knowledge test, and a Group A permit additionally requires passing the combination vehicle portion. Take air brakes in the same sitting: skip or fail it and the permit carries an air brake restriction that rules out virtually every tractor-trailer.
CDL Class A practice test49 CFR 383.25(a)(3), 383.135(a)(2)–(3)
Study Section 6 (Combination Vehicles) and Section 5 (Air Brakes) of your state’s CDL manual
In the AAMVA model manual most states publish, combination vehicles is Section 6: driving combinations, coupling and uncoupling, and inspecting a combination vehicle. The three federal knowledge areas above are what the questions are built from; drill the practice set on this page until you are consistently above 80%.
Pass the combination knowledge test at your state licensing agency
You need at least 80%, the federal pass mark for every CDL knowledge test. Under the AAMVA model the combination test has 20 questions — 16 correct to pass — though your state can use a different count. Testing fees, appointment rules and retake waits vary by state; the state pages below name the agency that issues your license.
Find your state’s combination practice test and agency49 CFR 383.135(a)(1)
Complete entry-level driver training before your first Class A skills test
If your learner’s permit was issued on or after February 7, 2022, you must complete Class A entry-level driver training — theory plus behind-the-wheel — from a provider listed on FMCSA’s Training Provider Registry before taking the Class A skills test for the first time. That includes Class B holders upgrading to Class A.
49 CFR 383.71(a)(10), 383.71(e)(5), 380.603
Take the skills test in a representative tractor-trailer with a fifth wheel
The skills test must be taken in a vehicle representative of the group you want. Test in a Group A combination connected by a pintle hook or other non-fifth-wheel hitch and your CDL gets the tractor-trailer restriction (code O); test without air brakes and you get the air brake restriction. You are not eligible for the skills test in the first 14 days after the permit is issued.
49 CFR 383.71(b)(2), 383.95(a) and (d), 383.135(b)(6), 383.153(a)(10), 383.25(e)
Pulling doubles or triples? Add the T endorsement
Double and triple trailers need their own endorsement — a knowledge test only, no skills test — covering hookup, trailer placement and the handling of multi-trailer combinations.
Doubles & Triples endorsement practice test49 CFR 383.93(b)(1) and (c)(1)
CDL combination vehicles test — questions and answers
Is the combination vehicles test required for a Class A CDL?
Yes. Federal rule is explicit: an applicant who fails the combination vehicle portion of the knowledge test must not be issued a Group A learner’s permit or CDL. It is not required for Class B or Class C.
49 CFR 383.135(a)(3)
How many questions are on the combination test, and what score do I need?
Under the AAMVA model most states use, the combination vehicles test has 20 questions; the federal pass mark of 80% means 16 correct. Your state can use a different count — check its CDL manual. The practice set on this page plays 20 questions with explanations.
49 CFR 383.135(a)(1)
Is combination vehicles an endorsement?
No — it is a required knowledge test for the Class A group, with no code printed on the license. Doubles/triples, by contrast, is an endorsement (code T) with its own knowledge test.
49 CFR 383.93(b)(1), 383.153(a)(9)(i)
Do I also need the air brakes test?
In practice, yes. The federal combination knowledge areas include air brakes, and if you fail the air brake component or test in a vehicle without air brakes, your CDL is restricted from any air-braked CMV — which is nearly every tractor-trailer.
CDL Air Brakes practice test49 CFR 383.111(c)(3), 383.95(a)
What is the tractor-trailer (O) restriction?
If you take the Class A skills test in a combination whose trailer is connected by a pintle hook or any other non-fifth-wheel connection, your CDL is restricted from operating a fifth-wheel tractor-trailer. Removing it means retaking all three skills tests in a representative tractor-trailer.
49 CFR 383.95(d), 383.135(b)(6) and (b)(8), 383.153(a)(10)
Do I need ELDT before the Class A skills test?
Yes, if your learner’s permit was issued on or after February 7, 2022 and this is your first Class A — including an upgrade from Class B. Training must come from a provider listed on FMCSA’s Training Provider Registry. Drivers issued a Class A before that date are exempt for that license.
49 CFR 383.71(a)(10), 380.603(b)–(c)
Official sources
- 49 CFR 383.111 — Required knowledge (combination vehicles, paragraph (c))
- 49 CFR 383.135 — Passing knowledge and skills tests
- 49 CFR 383.91 — Commercial motor vehicle groups
- FMCSA Training Provider Registry
Fees, the licensing agency and appointment rules vary by state — pick your state below for the agency that issues your license.
Federal rules on this page last reviewed against the eCFR on .
Practice the Combination Vehicles test by state
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