CDL COMBINATION VEHICLE PRACTICE TEST
ASSESSMENT SCRIPT 2026 VERIFIED
ANSWERS COMPREHENSIVE REVIEW
◉ When uncoupling a trailer, after you have shut off the trailer air
supply and locked the trailer brakes, you should:
Answer: Back up gently to ease pressure on the fifth wheel locking
jaws
◉ Semi-trailers made before 1975 that are equipped with air brakes:
Answer: Often do not have spring brakes
◉ Why should you be sure that the fifth wheel plate is greased as
required?
Answer: To prevent steering problems
◉ The trailer air supply control (also called the tractor protection
valve control) should automatically close when the air pressure falls
between:
Answer: 20 to 45 psi
◉ Your emergency air line breaks or gets pulled apart while you are
driving. The loss of air pressure will cause the:
, Answer: Emergency trailer brakes to come on
◉ A tractor-trailer vehicle combination is most likely to roll over in a
turn when the configuration includes:
Answer: Triple 27 ft. trailers
◉ Air lines on a combination vehicle are often to keep from getting
them mixed up. The emergency line is:
Answer: Red; the service line is blue
◉ Which of these statements is true?
Answer: Bobtail tractors can take longer to stop than a combination
vehicle loaded to maximum gross weight
◉ When checking that the trailer is securely coupled to the tractor,
the landing gear should be:
Answer: Slightly raised
◉ The safety latch for the fifth wheel locking lever must be:
Answer: Over the locking lever for coupling to be completed
◉ What will happen if the air lines are crossed when you hook up to
an old trailer?
ASSESSMENT SCRIPT 2026 VERIFIED
ANSWERS COMPREHENSIVE REVIEW
◉ When uncoupling a trailer, after you have shut off the trailer air
supply and locked the trailer brakes, you should:
Answer: Back up gently to ease pressure on the fifth wheel locking
jaws
◉ Semi-trailers made before 1975 that are equipped with air brakes:
Answer: Often do not have spring brakes
◉ Why should you be sure that the fifth wheel plate is greased as
required?
Answer: To prevent steering problems
◉ The trailer air supply control (also called the tractor protection
valve control) should automatically close when the air pressure falls
between:
Answer: 20 to 45 psi
◉ Your emergency air line breaks or gets pulled apart while you are
driving. The loss of air pressure will cause the:
, Answer: Emergency trailer brakes to come on
◉ A tractor-trailer vehicle combination is most likely to roll over in a
turn when the configuration includes:
Answer: Triple 27 ft. trailers
◉ Air lines on a combination vehicle are often to keep from getting
them mixed up. The emergency line is:
Answer: Red; the service line is blue
◉ Which of these statements is true?
Answer: Bobtail tractors can take longer to stop than a combination
vehicle loaded to maximum gross weight
◉ When checking that the trailer is securely coupled to the tractor,
the landing gear should be:
Answer: Slightly raised
◉ The safety latch for the fifth wheel locking lever must be:
Answer: Over the locking lever for coupling to be completed
◉ What will happen if the air lines are crossed when you hook up to
an old trailer?
