Written Knowledge Exam Practice

CDL Combination Vehicle (Class A) Written Knowledge Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is a combination vehicle?
• A vehicle with more than one axle
• A vehicle pulling one or more trailers
• A bus with passengers
• A vehicle that only drives in urban areas
• A vehicle pulling one or more trailers

Rationale: Combination vehicles are trucks that tow one or more

trailers, requiring special handling and knowledge of coupling and braking.

• Which part of a combination vehicle prevents the trailer from hitting

the cab during turns? 1 / 4

• Landing gear
• Fifth wheel
• Drive axle
• Kingpin
• Fifth wheel

Rationale: The fifth wheel allows pivoting of the trailer while keeping

it properly aligned behind the tractor, preventing contact with the cab.

3. When backing a trailer to the right, you should:

• Turn the steering wheel right
• Turn the steering wheel left
• Keep the wheels straight
• Use only mirrors without steering
• Turn the steering wheel left

Rationale: The trailer moves in the opposite direction of the tractor’s

turn; turning left moves the trailer to the right.

• What is the primary purpose of the trailer air supply control (yellow

knob)?

• Apply parking brakes
• Control air to the service brakes
• Supply air to the trailer brakes
• Operate the ABS system
• Supply air to the trailer brakes 2 / 4

Rationale: The yellow knob controls air pressure to the trailer brake

system, enabling safe connection and emergency braking.

• What is the main function of the tractor protection valve?
• Prevents air loss if the trailer breaks away
• Maintains engine temperature
• Locks the trailer in place
• Activates turn signals automatically
• Prevents air loss if the trailer breaks away

Rationale: The tractor protection valve closes if the trailer loses air,

preventing total brake failure in the tractor.

• When checking coupling, the tractor and trailer are properly

connected if:

• The fifth wheel is loose
• The kingpin is locked into the fifth wheel
• The trailer is leaning
• The landing gear is fully extended
• The kingpin is locked into the fifth wheel

Rationale: Proper coupling requires the kingpin to be fully engaged in

the fifth wheel to ensure a secure connection.

• Which system must be checked during a pre-trip inspection of a

combination vehicle?

• Air brakes on both tractor and trailer
• Fuel system only 3 / 4

• Windshield wipers only
• Horn and radio
• Air brakes on both tractor and trailer

Rationale: Both tractor and trailer air brakes are critical for safe

operation, especially on combination vehicles.

• What is “jackknife” in combination vehicles?
• Trailer swaying while parked
• Trailer and tractor folding at a sharp angle
• Tractor engine overheating
• Tire blowout
• Trailer and tractor folding at a sharp angle

Rationale: Jackknifing occurs when the trailer swings out during

braking or loss of traction, forming a sharp angle with the tractor.

• What is the main purpose of the emergency air line (red)?
• Operates the parking brakes
• Supplies air to the tractor
• Supplies air to the trailer in emergencies
• Controls engine braking
• Supplies air to the trailer in emergencies

Rationale: The red emergency line ensures the trailer brakes apply if

air supply is lost.

• When should you use the trailer hand brake?
• While driving downhill
• / 4