CDL Doubles Triples practice questions and answers 2026. Tap an option to test yourself — you'll see the correct answer and a plain-English explanation for every question. Free, no login.
Q11A driver is uncoupling a doubles set at a yard that has no level surface available. After setting the second trailer's parking brake and lowering the landing gear, the driver notices the landing gear pad is on soft ground. What must be done before disconnecting the dolly?
✓ Correct answer: B. Place wood blocking or cribbing under the landing gear pads to prevent them from sinking and destabilizing the trailer
The CDL manual states that when landing gear is on soft ground, wood or blocking must be placed under the landing gear pads to prevent sinking, which could cause the trailer to tip or the kingpin to bind when later attempting to recouple.
Q12When is it permissible to use the service brake hand valve to hold a doubles combination stationary during the coupling process?
✓ Correct answer: B. It is not permissible; the parking brakes of each trailer must be used to hold units stationary during coupling
The CDL manual requires each trailer's parking brakes to be set individually to hold that unit stationary during coupling procedures; the hand valve applies service brakes on moving vehicles and should not be relied upon as a stationary hold.
Q13After completing the full coupling of a triple combination and before departing, you perform a tug test by attempting to pull forward with the tractor while all trailer brakes are set. The tractor moves forward 18 inches before resistance is felt at the second coupling. What does this indicate?
✓ Correct answer: D. The converter dolly's pintle hook or the second trailer's kingpin coupling may not be fully engaged and must be re-inspected
The CDL manual states that a tug test should result in immediate resistance at all coupling points; movement at any coupling point before resistance indicates the coupling device is not fully engaged and must be reinspected and re-coupled.
Q14You are inspecting a triple combination and discover that the shut-off valve on the rear of the second trailer is in the closed position. What is the direct consequence if you depart without correcting this?
✓ Correct answer: B. Air will not reach the third trailer, leaving it without brakes
Shut-off valves on the rear of intermediate trailers must be open so air can pass through to supply the brakes on trailing units; a closed valve starves all rearward trailers of air pressure.
Q15On a set of doubles, how many shut-off (cut-out) valves does the FIRST trailer typically have on its rear for air-line connections to the converter dolly?
✓ Correct answer: A. Two — one for the service line and one for the emergency line
The CDL manual explains that each trailer in a combination has two rear shut-off valves — one for the service (control) line and one for the emergency (supply) line — so air can continue to rearward units.
Q16After connecting the gladhands between the first trailer and the converter dolly, a driver notices a continuous hissing sound at the connection point. What is the MOST LIKELY cause and the correct action?
✓ Correct answer: A. The gladhand seals are missing or damaged; replace the seals before departing
Hissing at gladhand connections indicates an air leak, most commonly caused by worn, missing, or improperly seated rubber seals; the CDL manual requires all air lines to be free of leaks before operation.
Q17During a pre-trip of a B-train doubles configuration, you find the converter dolly's pintle hook is visibly cracked. According to FMCSA inspection standards, which best describes the required action?
✓ Correct answer: D. The vehicle is out of service; the cracked pintle hook must be repaired or replaced before the combination moves
FMCSA regulations place a cracked coupling device in the out-of-service category because a failed pintle hook can cause a complete separation of the rear unit while in motion.
Q18When inspecting the electrical cable connecting the converter dolly to the second trailer, what condition makes the cable unacceptable for operation?
✓ Correct answer: D. The cable insulation is cracked and the bare wire is exposed
The CDL manual requires all electrical lines to have intact insulation; exposed bare wire creates a short-circuit hazard and can cause brake light or marker light failure on trailing units.
Q19When should shut-off valves on the rear of the LAST trailer in a triple combination be positioned?
✓ Correct answer: D. Closed, because no air lines connect behind the last trailer
The CDL manual states that shut-off valves on the rear of the rearmost trailer must be CLOSED because there are no further trailers to supply; leaving them open would bleed the entire system.
Q20A driver is inspecting a triple combination and finds that the safety chains between the converter dolly and the second trailer form a pronounced upward arc with 18 inches of slack. What is the correct assessment?
✓ Correct answer: B. Excessive slack is a defect; safety chains must be crossed under the tongue and have only enough slack to permit turns without binding
The CDL manual requires safety chains to be crossed under the converter dolly tongue and have limited slack so they can catch the tongue if the pintle hook fails, but not so tight they bind during turns — excessive slack defeats their purpose.
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