Doubles & Triples Endorsement Practice Test 2026
Free doubles and triples endorsement practice test for 2026: 20 questions with answers on hookup, trailer placement and stability, plus how to add the T.
What's on the Doubles & Triples 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 Doubles & Triples CDL knowledge test.
- Official test
- 20
- Practice questions here
- 20
- To pass
- 16/20 correct (80%)
- Updated
- September 2026
- 100% free
Doubles & Triples (T) endorsement at a glance
- Endorsement code
- T — double/triple trailers
- Test type
- Knowledge test only — no skills (driving) test
- Allowed on a learner’s permit
- No — T is not one of the three endorsements a CLP may carry; it goes on the full Class A
- Entry-level driver training
- Not required for the T endorsement
- Where to study
- The “Doubles and Triples” section of your state CDL manual (Section 7 in the model manual)
- 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
To ensure proper air flow to all trailers in double and triple rigs, what should you do after applying air to the service line?
- Go to the rear trailer, open the emergency line shut-off valve and listen for air escaping.
- Check the tire pressure on the second trailer.
- Disconnect the service line and observe for air pressure loss.
Correct answer: Go to the rear trailer, open the emergency line shut-off valve and listen for air escaping.
To make sure air gets to the brakes on all trailers in big trucks with more than one trailer, you should turn on the air to the brakes and then go to the last trailer. Open the valve that stops emergencies and listen for air hissing out. This tells you air is reaching all the way back.
When coupling a second trailer to your combination vehicle, what should you use to secure it?
- Both answers are correct
- The trailer's spring brakes and emergency air brakes
- Wheel chocks
Correct answer: Both answers are correct
When you are attaching a second trailer to your combination vehicle, you can use either the trailer's spring brakes and emergency air brakes or wheel chocks to secure it. Both methods are acceptable for keeping the trailer in place and ensuring safety.
While driving a 100-foot twin trailer combination at 50 mph under dry road conditions and good visibility, what is the recommended minimum amount of space you should maintain ahead of you, measured in seconds?
- 12
- 11
- 10
Correct answer: 11
If you're driving a big truck with two trailers at 50 mph on a dry road with clear weather, you should keep a space of at least 11 seconds ahead of you. This means you should be far enough behind the car in front of you so it takes you 11 seconds to reach where they are now. This gives you enough time to stop safely if you need to.
The most effective method to prevent brakes from overheating while descending a steep grade is to ___?
- Go 5 m.p.h. below your safe speed
- Use stab braking
- Use countersteering practices
- Use only the trailer brakes
Correct answer: Go 5 m.p.h. below your safe speed
The best way to keep your brakes from getting too hot when going down a steep hill is to go 5 miles per hour (mph) slower than the speed you feel is safe. This helps because it reduces how much you need to use your brakes, so they won't overheat as quickly.
Which of the following statements regarding the converter dolly uncoupling is true?
- Lower the landing gear before disconnecting the air lines.
- Ensure the dolly wheels are fully inflated before uncoupling.
- Do not unlock the pintle hook while the dolly is still under the rear trailer.
Correct answer: Do not unlock the pintle hook while the dolly is still under the rear trailer.
When dealing with a converter dolly, it's important to ensure safety by following certain procedures. One crucial step is to avoid unlocking the pintle hook while the dolly is still positioned under the rear trailer. This prevents the dolly from moving unexpectedly and causing accidents or damage.
In the “crack-the-whip” (rearward amplification) effect with trucks pulling multiple trailers, which unit is most likely to roll over?
- the first (front) trailer in a triple combination.
- the rear trailer of a triple.
- the tractor (power unit) at the front of the combination.
Correct answer: the rear trailer of a triple.
With double or triple combinations, each successive trailer is more prone to rolling over than the one ahead of it. In fact, the rear trailer of a triple is about 3.5 times more likely to roll over than a five-axle tractor-trailer. This increasing risk toward the back is called rearward amplification or the “crack-the-whip effect.” To reduce risk, put the heaviest trailer in front and the lightest in the rear.
What does the term “off-tracking” mean?
- A mechanical condition where the steering is misaligned and the vehicle pulls to one side on a straight road.
- How the rear wheels follow a different path from the front wheels in a turn
- When the trailer swings wide and the rear wheels follow the exact same track as the front wheels.
Correct answer: How the rear wheels follow a different path from the front wheels in a turn
Off-tracking refers to the fact that, during a turn, the front and rear wheels do not travel along the same path. The longer the vehicle, the more the rear wheels cut a different line. This means the tractor’s path is wider than the trailer/rig’s path, so you must steer wider to prevent the rig from riding over a curb or striking an object.
At what air pressure range does a truck protection valve automatically close to prevent air from escaping the truck?
- 20 PSI to 45 PSI
- 70 PSI to 80 PSI
- 30 PSI to 70 PSI
Correct answer: 20 PSI to 45 PSI
A truck protection valve stops air from leaking out of the truck. It does this by closing on its own if the air pressure falls between 20 to 45 PSI. This helps keep the brakes working right.
Is it true that the dolly tow bar might rise up if the pintle hook is unlocked while the converter dolly remains under the rear trailer?
- FALSE
- TRUE
Correct answer: TRUE
If you unlock the pintle hook while the converter dolly is still under the trailer, the tow bar can suddenly shoot up. This is dangerous. So, the correct answer is TRUE.
What precautions should be taken when connecting the converter dolly to the rear trailer?
- Raise the landing gear slightly off the ground
- Make sure trailer brakes are locked
- Make sure trailer height is correct
- All of the above
Correct answer: All of the above
When hooking up the converter dolly to the back trailer, check these: 1. The trailer's brakes must be set so it doesn't move. 2. Adjust the trailer so it's at the right height. 3. Lift the support legs just a bit off the ground. You need to do all these steps.
Some big trucks use convex or "spot" mirrors which:
- Reflect light to make driving at night easier
- Can be folded in when driving on highways to reduce wind resistance.
- Make things look larger and closer than the really are
- Make things look smaller and farther away than they really are
Correct answer: Make things look smaller and farther away than they really are
Some big trucks have special curved mirrors. These mirrors make stuff look smaller and further away than they actually are. This helps the driver see more around the truck.
When coupling twin/double trailers, if the rear trailer does not have spring brakes, ___.
- Ensure the service line is blocked before coupling.
- Make sure the service line is empty before coupling.
- The emergency line should be connected and disconnected to set the emergency brakes.
Correct answer: The emergency line should be connected and disconnected to set the emergency brakes.
If the second trailer lacks spring brakes, position the tractor near the trailer, attach the emergency line, pressurize the trailer's air tank, and then detach the emergency line. This process will activate the trailer's emergency brakes, provided the slack adjusters are properly adjusted.
You’re pulling doubles and one set of trailer wheels starts skidding. What is most likely to happen?
- The skid will quickly correct itself and the trailers will realign without any risk of jackknifing.
- You may jackknife.
- The only likely result is a tire blowout on the skidding trailer.
Correct answer: You may jackknife.
Use your mirrors to watch your trailers, especially after hard braking, to spot a skid early. When a trailer’s wheels begin to skid, the chance of a jackknife becomes high. If the trailer swings fully out of your lane, you may no longer be able to stop a jackknife.
When coupling a set of doubles, which method can you use to secure the second trailer before you couple it?
- Leave the second trailer unsecured and rely on the landing gear to keep it from moving.
- Lower the dolly legs and do not use any brakes or chocks.
- Hook up only the service line to secure the second trailer before coupling.
- Use wheel chocks.
Correct answer: Use wheel chocks.
If the second trailer has no spring brakes, you can pull the tractor close, connect the emergency line, charge the trailer’s air tank, then disconnect the emergency line to set the trailer’s emergency brakes (assuming the slack adjusters are properly adjusted). If you’re not sure the trailer’s brakes will hold, chock the wheels.
You are operating a triple trailer, and suddenly the emergency brakes for all three trailers engage. What caused it?
- The emergency line has lost air pressure.
- The service brake pedal is stuck.
- The trailers are not properly connected.
Correct answer: The emergency line has lost air pressure.
When the emergency brakes turn on by themselves in a triple trailer, it's probably because the emergency line has lost air pressure. This line carries air to the brakes, and if the pressure drops, the brakes automatically activate to stop the trailers.
The most effective method for resolving all skids is to ___.
- Counter steer and accelerate
- Restore traction to the tires
- Turn off the engine.
Correct answer: Restore traction to the tires
To stop a skid, make the tires grip the road again.
To prevent which potential issue should you assess your truck protection valve?
- The loss of air from the air hose
- All of the above
- The emergency brakes coming on due to loss of air
- The loss of air from your trailer brakes
Correct answer: All of the above
You should check your truck protection valve to stop your emergency brakes from suddenly working if you lose air, to prevent air from escaping your air hose, and to avoid losing air in your trailer brakes. So, the correct answer is to prevent all these issues.
What is the likely outcome if the pintle hook is unlocked while the converter dolly remains under the second trailer?
- The dolly wheels might detach.
- The dolly tow bar may fly up
- The lights on the trailer will go out.
- Nothing, the weight of the trailer will keep it in place
Correct answer: The dolly tow bar may fly up
If you unlock the pintle hook while the converter dolly is under the second trailer, the dolly tow bar may suddenly shoot upwards. This is because the pintle hook holds it in place, and removing that support without proper preparation can cause the tow bar to move unexpectedly.
Which statement regarding space management when operating double or triple trailers is incorrect?
- The trailers automatically adjust to traffic speed.
- Double trailers can be parked in compact car spaces.
- They do not need more space when turning or stopping.
Correct answer: They do not need more space when turning or stopping.
Double or triple trailers actually need more space when turning or stopping. These trailers are longer and more challenging to maneuver compared to a single trailer, so the statement saying they don't need more space is incorrect.
A converter dolly has a ______ wheel and ______ axles.
- fourth; one or two
- fifth; one or two
- third; one or two
Correct answer: fifth; one or two
A semitrailer can hook to a converter dolly because, like the back of a standard tractor, the dolly includes a fifth wheel and either one or two axles.
What the doubles/triples endorsement is — and who needs it
The doubles/triples endorsement — code T — is required to operate a commercial motor vehicle pulling double or triple trailers. It sits on top of a Class A CDL: a set of doubles is a combination over the Group A thresholds, so you need the Class A knowledge and skills tests — including the combination vehicles test, which is a hard gate for any Group A license — before the T means anything.
Federally, the T requires only a knowledge test; there is no separate skills test. It cannot be added at the permit stage, though: passenger, school bus and tank vehicle are the only endorsements a commercial learner’s permit may carry, so the T is added to the full CDL.
The endorsement certifies that you know how to assemble, place, brake and handle multi-trailer combinations. Where doubles and triples may actually run is governed by separate federal and state size-and-weight rules and by your carrier’s permits, not by the endorsement itself.
49 CFR 383.93(b)(1) and (c)(1), 383.153(a)(9)(i), 383.91(a)(1), 383.135(a)(3), 383.93(a)(2)
Drivers who need the T endorsement
Plan on the doubles/triples test if you will pull any of these:
- LTL linehaul sets — two 28-foot trailers behind a converter dolly, the most common doubles job in the country.
- Turnpike doubles and Rocky Mountain doubles where the route allows them.
- Triple-trailer combinations on the western routes that permit them.
- Any second trailer at all: the endorsement is about the number of trailers, not their length or weight.
- Not needed for a tractor with a single semi-trailer, however long — that is the Class A itself.
49 CFR 383.93(b)(1)
What is on the doubles/triples knowledge test
Federal rule fixes the subject matter every state’s doubles/triples test must cover. Expect questions on:
- Procedures for assembling and hooking up the units — converter dolly, pintle hook, safety chains, air and electrical lines.
- Proper placement of the heaviest trailer in the combination.
- Handling and stability: off-tracking, response to steering, sensory feedback, braking, oscillatory sway (the “crack-the-whip” effect), rollover in steady turns and yaw stability.
- Problems multi-trailer rigs create in traffic: slower speeds on steep grades, longer passing times, blocking freeway entries, splash and spray, aerodynamic buffeting, view blockages and lane placement.
- Inspecting doubles and triples and checking the air brakes on a multi-trailer combination.
49 CFR 383.115
How to add the doubles/triples endorsement to your CDL
Hold a Class A CDL
Doubles and triples are Group A combinations, so the T is added to a Class A license — which itself requires passing the combination vehicles knowledge test. A learner’s permit cannot carry the T endorsement.
CDL Class A practice test49 CFR 383.91(a)(1), 383.135(a)(3), 383.93(a)(2)
Study the doubles and triples section of your state’s CDL manual
In the AAMVA model manual most states publish, doubles and triples is Section 7: pulling double and triple trailers, coupling and uncoupling with a converter dolly, inspecting the combination and checking its air brakes. The 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 doubles/triples knowledge test at your state licensing agency
Doubles/triples is a knowledge-only endorsement — no skills test. You need at least 80%, the federal pass mark for every CDL knowledge test; under the AAMVA model the test has 20 questions, so 16 correct, though your state can use a different count. Testing and endorsement fees vary by state — the state pages below name the agency that issues your license.
Find your state’s doubles/triples practice test and agency49 CFR 383.93(c)(1), 383.135(a)(1)
Get the T printed on your license
States issue an endorsement only to drivers who pass the specialized test, and every state prints the same code letters. No entry-level driver training is required for the T endorsement — the ELDT rule applies to a first Class A or B license and to the passenger, school bus and hazmat endorsements.
49 CFR 383.93(a)(1), 383.153(a)(9)(i), 383.71(a)(10)
Check where your combination may run
The endorsement says you are qualified; it does not open a route. Which doubles and triples configurations are legal, and on which highways, is set by separate size-and-weight rules and by the permits your carrier holds — confirm with your carrier before running a new lane.
Doubles/triples endorsement — questions and answers
Is there a driving test for the doubles/triples endorsement?
No. Federal rule requires only a knowledge test for the double/triple trailers endorsement — the same as tanker and hazmat, and unlike passenger and school bus, which also require a skills test.
49 CFR 383.93(c)
Can I add the T endorsement to my learner’s permit?
No. Passenger, school bus and tank vehicle are the only endorsements allowed on a commercial learner’s permit. The T is added once you hold the Class A CDL.
49 CFR 383.93(a)(2)
How many questions are on the doubles/triples test, and what score do I need?
Under the AAMVA model most states use, the doubles/triples 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)
Do I need a Class A to pull doubles?
Yes. A double-trailer combination has a gross combination weight rating of 26,001 pounds or more with towed units rated over 10,000 pounds, which is the Group A definition — and a Group A license cannot be issued without passing the combination vehicles knowledge test.
CDL Combination practice test49 CFR 383.91(a)(1), 383.135(a)(3)
Which trailer goes first in a set of doubles?
The heavier trailer goes in front, directly behind the tractor, and the lighter one at the rear — a light trailer up front with a heavy one behind is far more likely to roll over or whip. Proper placement of the heaviest trailer is one of the federal knowledge areas, so expect it on the test.
49 CFR 383.115(b)
Do I need entry-level driver training (ELDT) for the T endorsement?
No. ELDT is required before a first Class A or Class B skills test, a first passenger or school bus skills test, or a first hazmat knowledge test. The doubles/triples endorsement is not on that list.
49 CFR 383.71(a)(10), 380.603
Official sources
- 49 CFR 383.115 — Requirements for double/triple trailers endorsement
- 49 CFR 383.93 — Endorsements
- 49 CFR 383.91 — Commercial motor vehicle groups
- FMCSA — Commercial Driver’s License
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 Doubles & Triples test by state
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