CDL - Combination Vehicle Practice Test
A tractor with a(n) ________ trailer requires the shortest amount of stopping distance .
1. empty
2. fully loaded
3. lightly loaded - 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 - 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 - you could lose your brakes while driving
Which part of the kingpin should the locking jaws close around? - The shank
Glad hands are used to connect the ....
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 - 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 - 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 - 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 - 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
3. back section - 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 - 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 - 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 - 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 - check the air line connections
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 - 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 - 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 - Never
A tractor with a(n) ________ trailer requires the shortest amount of stopping distance .
1. empty
2. fully loaded
3. lightly loaded - 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 - 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 - you could lose your brakes while driving
Which part of the kingpin should the locking jaws close around? - The shank
Glad hands are used to connect the ....
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 - 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 - 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 - 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 - 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
3. back section - 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 - 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 - 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 - 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 - check the air line connections
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 - 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 - 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 - Never
