Doubles and triples practice test
The doubles and triples test earns the T endorsement. It builds on the combination vehicles test with the extra risks of multiple trailers: the crack-the-whip effect, coupling a converter dolly, and checking the air system across every trailer. The sample questions below come from Section 7 of the FMCSA CDL manual.
- 20questions on the real test
- 80%pass mark, 16 correct answers
- 40questions in the PassRig bank
- S7of the FMCSA CDL manual
Free doubles/triples practice quiz
Ten questions from the PassRig bank. Tap an answer to lock it in and read why it is right, with the manual section it comes from. The score keeps count; 80% is the pass mark. The full bank, timed mock exams and mistake review live in the app.
0 of 10 right0 of 10 answered
The "crack-the-whip" effect is most dangerous for which vehicle?
Answer: C. The rear trailer of a set of triplesDoubles and triples are more likely to turn over than other combination vehicles because of the crack-the-whip effect, and the last trailer in a combination is the one most likely to turn over. Steer gently when pulling trailers.
Source: FMCSA CDL Manual, Section 7.1.2 (Beware of the Crack-the-Whip Effect)
In a set of doubles, which trailer should be directly behind the tractor?
Answer: B. The heavier oneFor the safest handling on the road, the more heavily loaded semitrailer should be in first position behind the tractor, and the lighter trailer should be in the rear.
Source: FMCSA CDL Manual, Section 7.2.1 (Coupling Double Trailers: Secure the Second (Rear) Trailer)
If you cross the air lines between a tractor and an old trailer with no spring brakes, what happens?
Answer: B. You could drive away with no trailer brakes at allCrossed lines send supply air to the service line instead of charging the trailer air tanks. On a trailer with spring brakes the brakes will not release and you notice. On an older trailer without spring brakes you can drive away with no trailer brakes, which is very dangerous. Always test the trailer brakes before driving.
Source: FMCSA CDL Manual, Section 6.2.5 (Hose Couplers (Glad Hands))
When inspecting the air lines between the trailers of a set of doubles or triples, you should check that they are:
Answer: B. Supported, properly connected to the glad hands with no leaks, and secured with enough slack for turnsThe inspection checks that the air lines are supported and the glad hands are properly connected, with no air leaks, and that the lines are properly secured with enough slack for turns and free from damage. The light cords must be firmly connected in the trailer sockets.
Source: FMCSA CDL Manual, Section 7.3.1 (Additional Checks: Double and Triple Trailers)
A sudden movement of the steering wheel in a set of doubles or triples can:
Answer: D. Tip over a trailer, so you must steer gentlyIf you make a sudden movement with your steering wheel, your trailer could tip over because of the crack-the-whip effect. Steer gently and smoothly, and look far enough down the road to avoid being surprised into a sudden lane change.
Source: FMCSA CDL Manual, Section 7.1.2 (Beware of the Crack-the-Whip Effect) and 6.1.2 (Steer Gently)
To move a converter dolly into position by hand, you first release its brakes by:
Answer: D. Opening the air tank petcock, or using the dolly parking brake control if it has spring brakesThe dolly's brakes hold it still. Release them by opening the air tank petcock, or, if the dolly has spring brakes, use the dolly parking brake control. Then wheel the dolly into position by hand so it is in line with the kingpin.
Source: FMCSA CDL Manual, Section 7.2.1 (Coupling Double Trailers: Position the Converter Dolly in Front of the Second (Rear) Trailer)
After coupling the dolly to the second trailer, a visual check should show:
Answer: A. No space between the upper and lower fifth wheel, and the locking jaws closed around the kingpinA gap between the fifth wheel plates or open jaws means the trailer is not locked on. Pulling against the pin tests the coupling, but you must also make a visual check to confirm it.
Source: FMCSA CDL Manual, Section 7.2.1 (Coupling Double Trailers: Connect the Converter Dolly to the Rear Trailer)
Never unlock the pintle hook while the converter dolly is still under the rear trailer because:
Answer: D. The dolly tow bar may fly up, injuring you and making it very hard to re-coupleWith the trailer's weight on the dolly, the tow bar can fly up when the pintle hook is released. Pull the dolly out from under the rear trailer first, lower the dolly landing gear, disconnect the safety chains and set the dolly brakes or chock its wheels, and only then release the pintle hook.
Source: FMCSA CDL Manual, Section 7.2.2 (Uncoupling the Double Trailers: Uncouple the Converter Dolly)
During the inspection of doubles or triples, you should check that the pintle hook is:
Answer: A. Latched, with the safety chains securedBe sure the pintle eye of the dolly is in place in the pintle hook of the trailer, make sure the pintle hook is latched, and check that the safety chains are secured to the trailer. If the hook is not latched the trailer can break away.
Source: FMCSA CDL Manual, Section 7.3.1 (Additional Checks: Double and Triple Trailers)
To test the trailer service brakes, you:
Answer: D. Release the parking brakes, move forward slowly, and apply the trailer brakes with the hand control; you should feel them come onFeeling the brakes come on when you use the hand control (trolley valve) tells you the trailer brakes are connected and working. The trailer brakes are tested with the hand valve but controlled in normal driving with the foot pedal, which applies the service brakes at all wheels.
Source: FMCSA CDL Manual, Section 7.4.1 (Test the Trailer Service Brakes)
What the doubles/triples test covers
- Pulling double and triple trailers: rollover and crack-the-whip
- Coupling and uncoupling twin trailers and converter dollies
- Inspecting doubles and triples
- Checking the air brakes on multiple trailers
- Managing space and following distance with long combinations
Who needs it
Drivers who want the T endorsement to pull two or three trailers. You need a Class A CDL first.
The test has 20 multiple-choice questions and the passing score is 80%, so you can miss 4. Your state DMV or DOT administers it; the federal rules are on the FMCSA CDL page. Study Section 7 of the CDL manual alongside these questions.
More CDL practice tests
Guides for this test
Doubles/Triples test questions
How many questions are on the doubles and triples test?
20 questions. 16 correct answers reach the 80% pass mark.
Do I need the combination vehicles test before doubles and triples?
Yes. The T endorsement sits on top of a Class A CDL, and Class A already requires the combination vehicles knowledge test.
Are triples legal everywhere?
No. Several states do not allow triples at all, and routes are restricted. The endorsement test is the same, but check your state DMV or DOT and the carrier's route rules.