CDL - COMBINATION VEHICLE PRACTICE TEST EXAM 200
ACTUAL QUESTIONS AND CORRECT ANSWERS WITH
RATIONALE ALREADY GRADED A+ LATEST 2026
This comprehensive 200-question CDL Combination Vehicle practice exam
covers all essential knowledge areas required for the commercial driver's
license endorsement test. The questions address coupling and uncoupling
procedures, air brake systems, fifth wheel operations, trailer types, doubles
and triples combinations, off-tracking, crack-the-whip effect, rollover
prevention, jackknife avoidance, and proper cargo loading. Critical safety
topics include pre-trip inspections, tractor protection valves, glad hand
connections, landing gear operations, and brake testing procedures. Each
question provides practical, real-world scenarios with detailed rationales to
reinforce understanding. This resource emphasizes the safe operation,
inspection, and emergency response skills necessary for professional
combination vehicle drivers.
1. What part of the kingpin should the fifth wheel locking jaws close around?
A) The head
B) The shank
C) The base
D) The safety latch
Answer: B
Explanation: The locking jaws of the fifth wheel are designed to close securely
around the shank of the kingpin, which is the smooth, cylindrical middle section.
This ensures a safe and secure connection between the tractor and trailer.
2. When inspecting the landing gear after uncoupling the trailer, where should the
tractor be positioned?
A) With the fifth wheel directly beneath the kingpin
B) Completely cleared from the trailer
C) With the tractor frame under the trailer
D) At a 45-degree angle to the trailer
Answer: C
Explanation: The tractor should be positioned with its frame under the trailer
during this inspection to provide support and ensure the landing gear is properly
assessed before the tractor is completely pulled away.
,3. How much space should there be between the upper and lower fifth wheel after
coupling?
A) Just enough to see light through it
B) About 1/4 inch
C) None
D) Approximately 1/2 inch
Answer: C
Explanation: After proper coupling, there should be no gap between the upper and
lower fifth wheel plates. The trailer apron should rest firmly on the fifth wheel
plate without any visible space.
4. When checking the trailer emergency brakes, how should the tractor protection
control valve be positioned?
A) Normal
B) Emergency
C) Neutral
D) Off
Answer: B
Explanation: To properly test the trailer emergency brakes, the tractor protection
control valve must be placed in the "emergency" position. This activates the
trailer's emergency brake system for inspection.
5. What is the primary purpose of the trailer hand valve?
A) To park the vehicle on a grade
B) To test the trailer brakes
C) To control the trailer brakes while driving
D) To activate the trailer's emergency brakes
Answer: B
Explanation: The trailer hand valve should be used only to test the trailer brakes. It
should not be used for parking or as a primary braking method while driving.
6. After coupling the trailer, how should you begin raising the landing gear?
A) Using high gear
B) Using low gear
C) Using intermediate gear
D) Using neutral
Answer: B
,Explanation: Low gear should be used when initially raising the landing gear after
coupling. This provides the necessary mechanical advantage to lift the heavy trailer
weight safely.
7. What is the consequence of crossing the air lines when hooking up to an old
trailer?
A) The trailer brakes will not release
B) The tractor brakes will lock up
C) The emergency and service functions will be reversed
D) The air pressure will drop to zero
Answer: C
Explanation: Crossing the air lines on an older trailer will reverse the emergency
and service line functions. This can cause improper brake operation and create a
serious safety hazard.
8. Which type of truck-trailer combination has the greatest chance of a "crack-the-
whip" rollover?
A) A single tractor trailer
B) A tractor pulling two trailers
C) A tractor pulling three trailers
D) A tractor pulling a single flatbed
Answer: C
Explanation: A tractor pulling three trailers has the greatest chance of a "crack-the-
whip" rollover. The more trailers in the combination, the greater the amplification
of the lateral forces that can cause this dangerous effect.
9. How should air and electrical lines from the tractor to the trailer be arranged?
A) Pulled tight with very little slack
B) Secured but with enough slack for turns
C) Resting on the frame of the tractor
D) Tied together with rubber bands
Answer: B
Explanation: Air and electrical lines must be secured but have enough slack to
allow for turns. This prevents the lines from pulling tight or becoming damaged
during normal driving maneuvers.
10. When uncoupling a loaded trailer, how far should you lower the landing gear?
A) Until it reaches the ground
B) Until it makes firm contact with the ground
C) Until the trailer is completely off the fifth wheel
, D) Until it just touches the ground
Answer: B
Explanation: The landing gear should make firm contact with the ground when
uncoupling a loaded trailer. This ensures the trailer is properly supported before the
tractor is pulled away.
11. If the fifth wheel locking lever is not locked after the jaws close around the
kingpin, what does this indicate?
A) The parking lock is off and you may drive away
B) The coupling is not right and should be fixed before driving
C) The trailer will not swivel on the fifth wheel
D) The brakes are engaged
Answer: B
Explanation: If the locking lever is not locked after coupling, the connection is not
secure and must be fixed before driving. This is a critical safety check that must be
verified before operation.
12. What is the purpose of glad hands on a combination vehicle?
A) To connect the kingpin to the locking jaws of the fifth wheel
B) To connect the electrical lines from the tractor to the trailer
C) To connect the service and emergency air lines from the tractor to the trailer
D) To connect the brake chambers to the slack adjusters
Answer: C
Explanation: Glad hands are the coupling devices used to connect the service and
emergency air lines between the tractor and the trailer. They are typically color-
coded (red for emergency, blue for service) to prevent connection errors.
13. When parking a trailer without spring brakes, why should you use wheel
chocks?
A) Because some states require chocking of trailer wheels
B) Because if the air supply leaks away, there will be no brakes
C) Because you don't want the trailer rolling down a hill
D) Because chocks are required by federal law
Answer: B
Explanation: A trailer without spring brakes relies on air pressure to keep its brakes
applied. If the air supply leaks away, the brakes will release. Wheel chocks provide
a mechanical means of keeping the trailer from moving.
14. While driving a combination vehicle, what happens if the service line
disconnects but the emergency line remains connected?
ACTUAL QUESTIONS AND CORRECT ANSWERS WITH
RATIONALE ALREADY GRADED A+ LATEST 2026
This comprehensive 200-question CDL Combination Vehicle practice exam
covers all essential knowledge areas required for the commercial driver's
license endorsement test. The questions address coupling and uncoupling
procedures, air brake systems, fifth wheel operations, trailer types, doubles
and triples combinations, off-tracking, crack-the-whip effect, rollover
prevention, jackknife avoidance, and proper cargo loading. Critical safety
topics include pre-trip inspections, tractor protection valves, glad hand
connections, landing gear operations, and brake testing procedures. Each
question provides practical, real-world scenarios with detailed rationales to
reinforce understanding. This resource emphasizes the safe operation,
inspection, and emergency response skills necessary for professional
combination vehicle drivers.
1. What part of the kingpin should the fifth wheel locking jaws close around?
A) The head
B) The shank
C) The base
D) The safety latch
Answer: B
Explanation: The locking jaws of the fifth wheel are designed to close securely
around the shank of the kingpin, which is the smooth, cylindrical middle section.
This ensures a safe and secure connection between the tractor and trailer.
2. When inspecting the landing gear after uncoupling the trailer, where should the
tractor be positioned?
A) With the fifth wheel directly beneath the kingpin
B) Completely cleared from the trailer
C) With the tractor frame under the trailer
D) At a 45-degree angle to the trailer
Answer: C
Explanation: The tractor should be positioned with its frame under the trailer
during this inspection to provide support and ensure the landing gear is properly
assessed before the tractor is completely pulled away.
,3. How much space should there be between the upper and lower fifth wheel after
coupling?
A) Just enough to see light through it
B) About 1/4 inch
C) None
D) Approximately 1/2 inch
Answer: C
Explanation: After proper coupling, there should be no gap between the upper and
lower fifth wheel plates. The trailer apron should rest firmly on the fifth wheel
plate without any visible space.
4. When checking the trailer emergency brakes, how should the tractor protection
control valve be positioned?
A) Normal
B) Emergency
C) Neutral
D) Off
Answer: B
Explanation: To properly test the trailer emergency brakes, the tractor protection
control valve must be placed in the "emergency" position. This activates the
trailer's emergency brake system for inspection.
5. What is the primary purpose of the trailer hand valve?
A) To park the vehicle on a grade
B) To test the trailer brakes
C) To control the trailer brakes while driving
D) To activate the trailer's emergency brakes
Answer: B
Explanation: The trailer hand valve should be used only to test the trailer brakes. It
should not be used for parking or as a primary braking method while driving.
6. After coupling the trailer, how should you begin raising the landing gear?
A) Using high gear
B) Using low gear
C) Using intermediate gear
D) Using neutral
Answer: B
,Explanation: Low gear should be used when initially raising the landing gear after
coupling. This provides the necessary mechanical advantage to lift the heavy trailer
weight safely.
7. What is the consequence of crossing the air lines when hooking up to an old
trailer?
A) The trailer brakes will not release
B) The tractor brakes will lock up
C) The emergency and service functions will be reversed
D) The air pressure will drop to zero
Answer: C
Explanation: Crossing the air lines on an older trailer will reverse the emergency
and service line functions. This can cause improper brake operation and create a
serious safety hazard.
8. Which type of truck-trailer combination has the greatest chance of a "crack-the-
whip" rollover?
A) A single tractor trailer
B) A tractor pulling two trailers
C) A tractor pulling three trailers
D) A tractor pulling a single flatbed
Answer: C
Explanation: A tractor pulling three trailers has the greatest chance of a "crack-the-
whip" rollover. The more trailers in the combination, the greater the amplification
of the lateral forces that can cause this dangerous effect.
9. How should air and electrical lines from the tractor to the trailer be arranged?
A) Pulled tight with very little slack
B) Secured but with enough slack for turns
C) Resting on the frame of the tractor
D) Tied together with rubber bands
Answer: B
Explanation: Air and electrical lines must be secured but have enough slack to
allow for turns. This prevents the lines from pulling tight or becoming damaged
during normal driving maneuvers.
10. When uncoupling a loaded trailer, how far should you lower the landing gear?
A) Until it reaches the ground
B) Until it makes firm contact with the ground
C) Until the trailer is completely off the fifth wheel
, D) Until it just touches the ground
Answer: B
Explanation: The landing gear should make firm contact with the ground when
uncoupling a loaded trailer. This ensures the trailer is properly supported before the
tractor is pulled away.
11. If the fifth wheel locking lever is not locked after the jaws close around the
kingpin, what does this indicate?
A) The parking lock is off and you may drive away
B) The coupling is not right and should be fixed before driving
C) The trailer will not swivel on the fifth wheel
D) The brakes are engaged
Answer: B
Explanation: If the locking lever is not locked after coupling, the connection is not
secure and must be fixed before driving. This is a critical safety check that must be
verified before operation.
12. What is the purpose of glad hands on a combination vehicle?
A) To connect the kingpin to the locking jaws of the fifth wheel
B) To connect the electrical lines from the tractor to the trailer
C) To connect the service and emergency air lines from the tractor to the trailer
D) To connect the brake chambers to the slack adjusters
Answer: C
Explanation: Glad hands are the coupling devices used to connect the service and
emergency air lines between the tractor and the trailer. They are typically color-
coded (red for emergency, blue for service) to prevent connection errors.
13. When parking a trailer without spring brakes, why should you use wheel
chocks?
A) Because some states require chocking of trailer wheels
B) Because if the air supply leaks away, there will be no brakes
C) Because you don't want the trailer rolling down a hill
D) Because chocks are required by federal law
Answer: B
Explanation: A trailer without spring brakes relies on air pressure to keep its brakes
applied. If the air supply leaks away, the brakes will release. Wheel chocks provide
a mechanical means of keeping the trailer from moving.
14. While driving a combination vehicle, what happens if the service line
disconnects but the emergency line remains connected?
