CDL - Combination Vehicle Practice Test
actual exam questions and answers with
latest version and complete solutions 2026.
A tractor with a(n) ________ trailer requires the shortest amount of
stopping distance .
1. empty
2. fully loaded
3. lightly loaded - ANSWER: fully loaded
The air leakage rate for a combination vehicle ( engine off, brakes on)
should not be more than _____ psi per minute .
1. 4
2. 6
3. 2 - ANSWER: 4
If you do not do the final air brake check for air leaks and fix them
before driving,
1. you could lose your brakes while driving
2. your fuel usage will increase
3. tire pressure will drop - ANSWER: you could lose your brakes while
driving
Which part of the kingpin should the locking jaws close around? -
ANSWER: The shank
Glad hands are used to connect the ....
1|Page
,1. kingpin from the trailer to the locking jaws of the fifth wheel
2. electrical lines from the tractor to the trailer
3. service and emergency air lines from the truck or tractor to the
trailer - ANSWER: service and emergency air lines from the truck or
tractor to the trailer
Trucks roll over more easily when fully loaded and are
1. ten times more likely to roll over in a crash than empty rigs
2. five times more likely to roll over in a crash than empty rigs
3. two times more likely to roll over in a crash than empty rigs -
ANSWER: ten times more likely to roll over in a crash than empty rigs
In general, the higher your trucks center of gravity, the ...
1. easier it is to turn over
2. more stable it is when turning
3. easier it is to turn around corners - ANSWER: easier it is to turn over
You are driving a combination vehicle when the trailer breaks away,
pulling apart both air lines. You would expect the trailer brakes to come
on and ...
1. the tractor to lose all air pressure
2. the tractor protection valve to close
3. the trailer supply valve to stay open - ANSWER: the tractor protection
valve to close
When you drive a set of doubles, which shut-off valve must be closed in
the last trailer?
1. Middle section
2. front section
2|Page
,3. back section - ANSWER: back section
The fifth wheel locking lever is not locked after the jaws close around
the kingpin. This means that...
1. the parking lock is off and you may drive away
2. the trailer will not swivel on the fifth wheel
3. the coupling is not right and should be fixed before you drive the
coupled unit - ANSWER: the coupling is not right and should be fixed
before you drive the coupled unit
What gear should the tractor engine be in after you uncouple the trailer
and are inspecting the trailer?
1. neutral
2. low reverse
3. high reverse - ANSWER: neutral
After you supply air to the trailer, make sure the air lines are not
crossed and the trailer brakes are working. This is done by ..
1. lifting the brake pedal
2. applying and releasing the trailer brakes and listening for brake
sounds
3. turning on the parking brake from the cab - ANSWER: applying and
releasing the trailer brakes and listening for brake sounds
If the brakes did not release when you pushed the trailer air supply
valve, you should ...
1. cross the air lines,
2. check the air line connections
3. check the electrical cables - ANSWER: check the air line connections
3|Page
, You have a major leak in the service line, and you apply the brakes.
Service air pressure will escape and cause the
1. trailer tank pressure to be lost
2. trailer emergency brakes to come on
3. tractor spring brakes to lock on - ANSWER: trailer emergency brakes
to come on
You are uncoupling a trailer. After you shut off the trailer air supply and
lock the trailer brakes, you should
1. immediately apply your tractor parking brakes
2. begin to lower the trailer landing gear
3. back up gently and ease pressure on the fifth wheel locking jaws -
ANSWER: back up gently to ease pressure on the fifth wheel locking
jaws
When should you use the hand valve to park a combination vehicle?
1. To park at loading docks
2. To park on a grade
3. never - ANSWER: Never
The front trailer supports are up, and the trailer is resting on the
tractor. Make sure that
1. there is enough clearance between the upper and lower fifth wheel
2. there is enough clearance between the tractor frame and the landing
gear
3. the safety latch is in the unlocked position - ANSWER: there is
enough clearance between the tractor frame and the landing gear
4|Page
actual exam questions and answers with
latest version and complete solutions 2026.
A tractor with a(n) ________ trailer requires the shortest amount of
stopping distance .
1. empty
2. fully loaded
3. lightly loaded - ANSWER: fully loaded
The air leakage rate for a combination vehicle ( engine off, brakes on)
should not be more than _____ psi per minute .
1. 4
2. 6
3. 2 - ANSWER: 4
If you do not do the final air brake check for air leaks and fix them
before driving,
1. you could lose your brakes while driving
2. your fuel usage will increase
3. tire pressure will drop - ANSWER: you could lose your brakes while
driving
Which part of the kingpin should the locking jaws close around? -
ANSWER: The shank
Glad hands are used to connect the ....
1|Page
,1. kingpin from the trailer to the locking jaws of the fifth wheel
2. electrical lines from the tractor to the trailer
3. service and emergency air lines from the truck or tractor to the
trailer - ANSWER: service and emergency air lines from the truck or
tractor to the trailer
Trucks roll over more easily when fully loaded and are
1. ten times more likely to roll over in a crash than empty rigs
2. five times more likely to roll over in a crash than empty rigs
3. two times more likely to roll over in a crash than empty rigs -
ANSWER: ten times more likely to roll over in a crash than empty rigs
In general, the higher your trucks center of gravity, the ...
1. easier it is to turn over
2. more stable it is when turning
3. easier it is to turn around corners - ANSWER: easier it is to turn over
You are driving a combination vehicle when the trailer breaks away,
pulling apart both air lines. You would expect the trailer brakes to come
on and ...
1. the tractor to lose all air pressure
2. the tractor protection valve to close
3. the trailer supply valve to stay open - ANSWER: the tractor protection
valve to close
When you drive a set of doubles, which shut-off valve must be closed in
the last trailer?
1. Middle section
2. front section
2|Page
,3. back section - ANSWER: back section
The fifth wheel locking lever is not locked after the jaws close around
the kingpin. This means that...
1. the parking lock is off and you may drive away
2. the trailer will not swivel on the fifth wheel
3. the coupling is not right and should be fixed before you drive the
coupled unit - ANSWER: the coupling is not right and should be fixed
before you drive the coupled unit
What gear should the tractor engine be in after you uncouple the trailer
and are inspecting the trailer?
1. neutral
2. low reverse
3. high reverse - ANSWER: neutral
After you supply air to the trailer, make sure the air lines are not
crossed and the trailer brakes are working. This is done by ..
1. lifting the brake pedal
2. applying and releasing the trailer brakes and listening for brake
sounds
3. turning on the parking brake from the cab - ANSWER: applying and
releasing the trailer brakes and listening for brake sounds
If the brakes did not release when you pushed the trailer air supply
valve, you should ...
1. cross the air lines,
2. check the air line connections
3. check the electrical cables - ANSWER: check the air line connections
3|Page
, You have a major leak in the service line, and you apply the brakes.
Service air pressure will escape and cause the
1. trailer tank pressure to be lost
2. trailer emergency brakes to come on
3. tractor spring brakes to lock on - ANSWER: trailer emergency brakes
to come on
You are uncoupling a trailer. After you shut off the trailer air supply and
lock the trailer brakes, you should
1. immediately apply your tractor parking brakes
2. begin to lower the trailer landing gear
3. back up gently and ease pressure on the fifth wheel locking jaws -
ANSWER: back up gently to ease pressure on the fifth wheel locking
jaws
When should you use the hand valve to park a combination vehicle?
1. To park at loading docks
2. To park on a grade
3. never - ANSWER: Never
The front trailer supports are up, and the trailer is resting on the
tractor. Make sure that
1. there is enough clearance between the upper and lower fifth wheel
2. there is enough clearance between the tractor frame and the landing
gear
3. the safety latch is in the unlocked position - ANSWER: there is
enough clearance between the tractor frame and the landing gear
4|Page
