Maryland CDL Combination Vehicles Exam
With Actual Questions & Verified
Answers,Explained Rationales/Expert Verified
For Guaranteed Pass 2026/Latest
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1. What is the main purpose of a tractor protection valve in
combination vehicles?
A. To increase trailer braking power
B. To protect the tractor air supply if the trailer breaks away
C. To reduce fuel consumption
D. To regulate engine RPM
Answer: B
Rationale: The tractor protection valve automatically shuts off
air loss from the tractor if the trailer becomes disconnected or
has a major air leak, preserving braking capability on the
tractor.
2. When inspecting a fifth wheel coupling, what is most important to
check?
A. Tire tread depth
B. Proper lubrication only
C. Secure locking of the kingpin
D. Headlight alignment
Answer: C
Rationale: Ensuring the kingpin is securely locked into the fifth
wheel is critical to prevent trailer separation while driving.
3. What does a “crack-the-whip” effect refer to in combination
vehicles?
, A. Increased fuel efficiency in turns
B. Trailer swing becoming more severe than tractor movement
C. Engine overheating
D. Brake fade in cold weather
Answer: B
Rationale: The rear of a combination vehicle can swing wider
than the tractor during turns, creating a whip-like motion that
must be controlled.
4. Why is air pressure important in combination vehicle braking
systems?
A. It powers the radio system
B. It controls suspension height only
C. It operates service and emergency brakes
D. It improves steering response
Answer: C
Rationale: Air pressure is essential for activating both service
and emergency braking systems in air-brake-equipped
combination vehicles.
5. What is a converter dolly used for?
A. Carrying passengers
B. Connecting multiple trailers
C. Increasing horsepower
D. Stabilizing engine temperature
Answer: B
Rationale: A converter dolly allows a tractor to tow multiple
trailers by providing a connection point between them.
6. What is the correct order for coupling a tractor to a trailer?
A. Connect air lines first
B. Back under trailer, lock fifth wheel, connect lines
, C. Remove trailer wheels
D. Release brakes before connection
Answer: B
Rationale: The tractor must be backed under the trailer, fifth
wheel locked, then air and electrical lines connected properly.
7. What is a major risk when driving combination vehicles on curves?
A. Engine stall
B. Trailer off-tracking
C. Fuel overflow
D. Headlight failure
Answer: B
Rationale: Trailer off-tracking occurs when the trailer wheels
follow a shorter path than the tractor, increasing collision risk on
curves.
8. What should you do before uncoupling a trailer?
A. Increase engine RPM
B. Set trailer brakes and lower landing gear
C. Turn on hazard lights only
D. Remove air lines first
Answer: B
Rationale: Setting trailer brakes and lowering landing gear
stabilizes the trailer before disconnecting.
9. What is a dolly air tank used for?
A. Fuel storage
B. Air supply for brakes
C. Cooling system
D. Tire inflation
Answer: B
With Actual Questions & Verified
Answers,Explained Rationales/Expert Verified
For Guaranteed Pass 2026/Latest
Update/Instant Download Pdf
1. What is the main purpose of a tractor protection valve in
combination vehicles?
A. To increase trailer braking power
B. To protect the tractor air supply if the trailer breaks away
C. To reduce fuel consumption
D. To regulate engine RPM
Answer: B
Rationale: The tractor protection valve automatically shuts off
air loss from the tractor if the trailer becomes disconnected or
has a major air leak, preserving braking capability on the
tractor.
2. When inspecting a fifth wheel coupling, what is most important to
check?
A. Tire tread depth
B. Proper lubrication only
C. Secure locking of the kingpin
D. Headlight alignment
Answer: C
Rationale: Ensuring the kingpin is securely locked into the fifth
wheel is critical to prevent trailer separation while driving.
3. What does a “crack-the-whip” effect refer to in combination
vehicles?
, A. Increased fuel efficiency in turns
B. Trailer swing becoming more severe than tractor movement
C. Engine overheating
D. Brake fade in cold weather
Answer: B
Rationale: The rear of a combination vehicle can swing wider
than the tractor during turns, creating a whip-like motion that
must be controlled.
4. Why is air pressure important in combination vehicle braking
systems?
A. It powers the radio system
B. It controls suspension height only
C. It operates service and emergency brakes
D. It improves steering response
Answer: C
Rationale: Air pressure is essential for activating both service
and emergency braking systems in air-brake-equipped
combination vehicles.
5. What is a converter dolly used for?
A. Carrying passengers
B. Connecting multiple trailers
C. Increasing horsepower
D. Stabilizing engine temperature
Answer: B
Rationale: A converter dolly allows a tractor to tow multiple
trailers by providing a connection point between them.
6. What is the correct order for coupling a tractor to a trailer?
A. Connect air lines first
B. Back under trailer, lock fifth wheel, connect lines
, C. Remove trailer wheels
D. Release brakes before connection
Answer: B
Rationale: The tractor must be backed under the trailer, fifth
wheel locked, then air and electrical lines connected properly.
7. What is a major risk when driving combination vehicles on curves?
A. Engine stall
B. Trailer off-tracking
C. Fuel overflow
D. Headlight failure
Answer: B
Rationale: Trailer off-tracking occurs when the trailer wheels
follow a shorter path than the tractor, increasing collision risk on
curves.
8. What should you do before uncoupling a trailer?
A. Increase engine RPM
B. Set trailer brakes and lower landing gear
C. Turn on hazard lights only
D. Remove air lines first
Answer: B
Rationale: Setting trailer brakes and lowering landing gear
stabilizes the trailer before disconnecting.
9. What is a dolly air tank used for?
A. Fuel storage
B. Air supply for brakes
C. Cooling system
D. Tire inflation
Answer: B
