CDL Doubles and Triples Practice Test 2026: Practice test 2

Practice test 2 of 2 for the CDL Doubles and Triples Practice Test: 25 more questions with answers and explanations.

Commercial vehicle
United States
50 questions
Checked October 10, 2026

Question 1 of 25
After charging the trailer brakes, how do you check that air reaches the last trailer?
- Drive off and see whether the last trailer stops
- Look only at the tractor's air pressure gauge
- Open the rear emergency line shut-off and listen
- Check the tire pressure on the last trailer
Show answer
Answer: C. Open the rear emergency line shut-off and listen
Open the emergency shut-off at the back of the last trailer. If there is no air, the brakes won't work.
Question 2 of 25
You open the shut-off at the rear of the last trailer and hear no air. What is the most likely cause?
- The fifth wheel has too much grease
- The trailer lights are turned off
- A shut-off valve upstream is closed
- The tires on the last trailer are low
Show answer
Answer: C. A shut-off valve upstream is closed
If air does not reach the back, check that the shut-off valves on all trailers and the dolly are open.
Question 3 of 25
When uncoupling the rear trailer, where should you park the rig?
- On a curve
- On a slope so the trailer rolls free
- In a straight line on firm, level ground
- On soft ground
Show answer
Answer: C. In a straight line on firm, level ground
Park in a straight line on firm, level ground and apply the parking brakes before uncoupling.
Question 4 of 25
When uncoupling the rear trailer, why lower its landing gear first?
- To raise the trailer brakes
- To release the pintle hook
- To take some weight off the dolly
- To drain the air tanks
Show answer
Answer: C. To take some weight off the dolly
Lower the second trailer's landing gear enough to remove some weight from the dolly.
Question 5 of 25
When uncoupling, which shut-offs do you close before disconnecting the dolly lines?
- None; leave every shut-off open
- Only the shut-offs on the tractor
- The drain valves on the rear trailer
- Those at the rear of the first trailer
Show answer
Answer: D. Those at the rear of the first trailer
Close the air shut-offs at the rear of the first semitrailer, and on the dolly if it has them.
Question 6 of 25
How do you get the dolly out from under the rear trailer?
- Back the tractor and first trailer into the dolly
- Release the dolly fifth wheel latch and pull slowly forward
- Lift the rear trailer with a jack and roll the dolly out
- Unlock the pintle hook first and then drive away
Show answer
Answer: B. Release the dolly fifth wheel latch and pull slowly forward
Release the converter dolly fifth wheel latch, then slowly pull forward to draw the dolly out.
Question 7 of 25
Why must you never unlock the pintle hook with the dolly still under the rear trailer?
- The trailer lights may fail
- The dolly tow bar may fly up
- The air lines may freeze up
- The trailer may roll forward
Show answer
Answer: B. The dolly tow bar may fly up
The tow bar can fly up, causing injury and making it very hard to couple again.
Question 8 of 25
When unhooking the converter dolly from the first trailer, what do you do before releasing the pintle hook?
- Lower its gear, unhook the chains, and secure it
- Open all the shut-off valves on both trailers
- Raise the dolly landing gear all the way up
- Connect the light cord to the rear trailer
Show answer
Answer: A. Lower its gear, unhook the chains, and secure it
Lower the dolly's support, unhook the chains, and secure the dolly before releasing the pintle hook and pulling clear.
Question 9 of 25
How do you couple a set of triples?
- Hook the third trailer to the tractor first
- Use a fifth wheel between trailers and no dollies
- Couple the first trailer, then add the rest like doubles
- Couple all three trailers first, then back under them
Show answer
Answer: C. Couple the first trailer, then add the rest like doubles
Couple the tractor to the first trailer as for any semitrailer, then use the converter dolly method for the rest.
Question 10 of 25
When uncoupling triples, which trailer do you uncouple first?
- The third (last) trailer
- Any of the three
- The middle trailer
- The first trailer
Show answer
Answer: A. The third (last) trailer
Uncouple the third trailer by pulling the dolly out, then handle the rest like a double.
Question 11 of 25
You drive a combination type not covered in your manual. How should you couple it?
- Use the triples method for every rig
- Follow the maker's or owner's instructions
- Ask another driver to guess the steps
- Couple it any way that seems to work
Show answer
Answer: B. Follow the maker's or owner's instructions
There are many other combinations. Know the manufacturer and owner specifications for the vehicles you drive.
Question 12 of 25
During inspection of doubles, what position should the shut-off valves at the rear of the front trailer be in?
- Closed
- Open
- Removed
- Halfway
Show answer
Answer: B. Open
Shut-offs at the rear of front trailers must be open so air flows back. Only those at the rear of the last trailer are closed.
Question 13 of 25
During inspection, what position should the converter dolly air tank drain valve be in?
- Removed
- Closed
- Open
- It does not matter
Show answer
Answer: B. Closed
The converter dolly air tank drain valve should be closed.
Question 14 of 25
What should you check on the pintle hook during inspection?
- The hook is freshly painted and clean
- The pintle eye is in the hook and it is latched
- The hook is mounted under the last trailer
- The hook is open so it releases easily
Show answer
Answer: B. The pintle eye is in the hook and it is latched
The dolly pintle eye must be in the trailer's pintle hook, and the hook must be latched.
Question 15 of 25
Which of these should you check on a double during the walkaround?
- Safety chains removed so they don't drag
- Light cords left loose for easy unplugging
- Safety chains secured and light cords firmly plugged in
- Air lines resting on the ground between trailers
Show answer
Answer: C. Safety chains secured and light cords firmly plugged in
Check that safety chains are secured, light cords are firmly in place, and air lines are supported.
Question 16 of 25
Your converter dolly carries a spare tire. What should you check?
- That it is chained to the pintle hook
- That it is removed for the trip
- That it is secured
- That it is flat
Show answer
Answer: C. That it is secured
Any spare tire on the converter dolly must be secured.
Question 17 of 25
For the air flow check on doubles, what do you do after pressure is normal?
- Pull out the yellow parking brake knob
- Turn off the battery switch in the cab
- Open all the drain valves on the trailers
- Push in the red knob, then use the hand brake
Show answer
Answer: D. Push in the red knob, then use the hand brake
Push in the red knob to supply the trailers, use the trailer hand brake to send air to the service line, then check at the rear.
Question 18 of 25
After checking the emergency line at the rear of the last trailer, what else should you check there?
- That service air reaches the last trailer
- That the tank drain valve is open
- That the trailer lights are switched off
- That the landing gear is lowered
Show answer
Answer: A. That service air reaches the last trailer
Open the service line valve at the rear to check that service pressure reaches all trailers, then close it.
Question 19 of 25
When testing the tractor protection valve on doubles, the control should pop out at about what pressure?
- About 150 psi
- About 20 to 45 psi
- About 125 psi
- About 100 psi
Show answer
Answer: B. About 20 to 45 psi
Lower the pressure by stepping on and off the brake. The control should pop out, usually between 20 and 45 psi.
Question 20 of 25
What could happen if the tractor protection valve does not work?
- The engine would overheat on long climbs
- The trailers would uncouple on their own
- A leak could drain the tractor's air supply
- The trailer lights would stay on all night
Show answer
Answer: C. A leak could drain the tractor's air supply
If the valve fails, a leak could drain all the tractor's air, applying the emergency brakes and possibly causing loss of control.
Question 21 of 25
How do you test the trailer emergency brakes on doubles?
- Pull out the trailer air supply, then pull gently
- Press the brake pedal hard at highway speed
- Unlock the pintle hook and drive forward
- Open the converter dolly's drain valve
Show answer
Answer: A. Pull out the trailer air supply, then pull gently
First make sure the trailers roll freely, then pull out the supply control and pull gently against the brakes.
Question 22 of 25
Which letter on a CDL shows the double/triple trailers endorsement?
- N
- S
- T
- X
Show answer
Answer: C. T
The T endorsement covers double and triple trailers.
Question 23 of 25
What kind of test is needed for the doubles/triples endorsement?
- A knowledge test and a skills test
- A skills test only
- No test
- A knowledge test only
Show answer
Answer: D. A knowledge test only
The double/triple trailer endorsement requires a knowledge test.
Question 24 of 25
Can a commercial learner's permit (CLP) carry a doubles/triples (T) endorsement?
- Only for empty trailers
- Yes, if you are over 21
- No
- Yes, always
Show answer
Answer: C. No
Only passenger, school bus and tank endorsements are allowed on a CLP.
Question 25 of 25
Your double rig is 70 feet long and you are traveling at 50 mph. What following distance should you keep?
- At least 8 seconds
- At least 7 seconds
- At least 3 seconds
- At least 5 seconds
Show answer
Answer: A. At least 8 seconds
Allow 1 second for each 10 feet (7 seconds), plus 1 second because you are above 40 mph.

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