Combination Endorsement Test | Commercial Drivers License

Question 1 of 91

1 points

You are coupling a semi trailer to your tractor but have not yet backed under. The trailer is at the right height when:

It will be raised slightly when the tractor is backed under it.
The kingpin is about 1 1/4 inches above the fifth wheel.
The end of the kingpin is even with the top of the fifth wheel.

Question 2 of 91

1 points

You should not back a tractor under a trailer until the whole air system is:

Between 60 and 80 psi.
At normal pressure.
Bled down to half the maximum pressure.

Question 3 of 91

1 points

Which part of the kingpin should the locking jaws close around?

The base.
The shank.
The head.

Question 4 of 91

1 points

When you get ready to back under the semi trailer you should line up:

About 12 degrees off the line of the trailer.
The kingpin to engage the driver's side locking jaw first.
Directly in front of the trailer.

Question 5 of 91

1 points

How should you test the tractor semi trailer connection for security?

Pull gently forward in low gear against the locked trailer brakes, then look at it carefully.
Put the tractor in gear and pull ahead with a sharp jerk.
Rock the trailer back and forth with the trailer brakes locked.

Question 6 of 91

1 points

When should you use the hand valve to park a combination vehicle?

To park at loading docks.
Never.
To park on a grade.

Question 7 of 91

1 points

You supply air to the trailer tanks by:

Pushing in the trailer air supply valve.
Pulling out the trailer air supply valve.
Connecting the service line glad hand.

Question 8 of 91

1 points

Why should you be sure that the fifth wheel plate is greased as required?

To reduce heat and noise.
To prevent steering problems.
To ensure good electrical connections.

Question 9 of 91

1 points

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:

Applying and releasing the trailer brakes and listening for brake sounds.
Lifting the brake pedal.
Turning on the parking brakes from the cab.

Question 10 of 91

1 points

There are two things that a driver can do to prevent a roll over. They are: (1) Keep the cargo as close to the ground as possible; and (2):

Make sure that the brakes are properly adjusted.
Keep the fifth wheel's free play as tight as possible.
Go slowly around turns.

Question 11 of 91

1 points

Before you back under a trailer, make sure the:

Air supply knob is in.
Air brakes are off.
Trailer brakes are locked.

Question 12 of 91

1 points

If the service air line comes apart while you are driving a combination vehicle but the emergency line stays together, what will happen right away?

Nothing is likely to happen until you try to apply the brakes.
The trailer's air tank will exhaust through the open line.
The emergency tractor brakes will come on.

Question 13 of 91

1 points

The air leakage rate for a combination vehicle (engine off, brakes on) should not be more than ____ psi per minute.

4
6
2

Question 14 of 91

1 points

In normal driving, some drivers use the hand valve beforeapplying the brake pedal to prevent a jackknife. Which of these statements is true?

If the trailer has no spring brakes, you can drive away, but you will not have trailer brakes.
The brake pedal will work the trailer spring brakes instead of the air brakes.
The hand valve will apply the tractor brakes instead of the trailer brakes.

Question 15 of 91

1 points

Why should you lock the tractor glad hands (or dummy couplers) to each other when you are not towing a trailer?

The connected brake circuit becomes a back up air tank.
If you did not, you could never build system pressure.
It will keep dirt and water out of the lines.

Question 16 of 91

1 points

For coupling to be completed, the safety catch for the fifth wheel locking lever must be:

Straight up.
Over the locking lever.
Through the locking lever.

Question 17 of 91

1 points

The front trailer supports are up and the trailer is resting on the tractor. Make sure:

There is enough clearance between the upper and lower fifth wheel.
The safety latch is in the unlocked position.
There is enough clearance between the tractor frame and the landing gear.

Question 18 of 91

1 points

You have a major leak in the service line and you put on the brakes. Service air pressure will escape and cause the:

Trailer tank pressure to be lost.
Trailer emergency brakes to come on.
Tractor spring brakes to lock on.

Question 19 of 91

1 points

When backing under a tractor under a trailer you should expect:

Trailer will be lifted slightly when the tractor backs under it.
End of the kingpin is even with the top of the fifth wheel.
Trailer landing gear is fully extended.

Question 20 of 91

1 points

The driver crosses the air lines when hooking up to an old trailer. What will happen?

If the trailer has no spring brakes, you can drive away, but you will not have trailer brakes.
The brake pedal will work the trailer spring brakes instead of the air brakes.
The hand valve will apply the tractor brakes instead of the trailer brakes.

Question 21 of 91

1 points

You are coupling a tractor to a semi trailer and have backed up but are not under it. What should you hook up before backing under the semitrailer?

The emergency and service air lines.
The electrical service cable.
Nothing, back up and lock the fifth wheel.

Question 22 of 91

1 points

Air lines on a combination vehicle are often colored to keep them from getting mixed up. The emergency line is ____; the service line is ____.

Red, blue
Blue, red
Black, yellow

Question 23 of 91

1 points

Which of these statements is true?

Light vehicles need more braking power to stop than heavy ones.
Always delay braking a heavy vehicle until you have no other choice.
"Bobtail" tractors can take longer to stop than a combination vehicle loaded to the maximum gross weight.

Question 24 of 91

1 points

After connecting the air lines, but before backing under the trailer you should:

Make sure that the trailer brakes are off.
Supply air to the trailer system, then pull out the air supply knob.
Walk around the rig to make sure it is clear.

Question 25 of 91

1 points

The hand valve should be used:

To test the trailer brakes.
Only when the trailer is fully loaded.
Only with the foot brake.

Question 26 of 91

1 points

The air leakage rate for a combination vehicle (engine off, brakes off) should be no more than ____ psi per minute.

2
3
4

Question 27 of 91

1 points

The fifth wheel locking lever is not locked after the jaws close around the kingpin. This means that:

You can set the fifth wheel for weight balance.
The coupling is not right and should be fixed before driving the vehicle.
The parking lock is off and you may drive away.

Question 28 of 91

1 points

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:

The trailer supply valve to stay open.
The tractor to lose all air pressure.
The tractor protection valve to close.

Question 29 of 91

1 points

Semi trailers made before 1975 that are equipped with air brakes:

Often do not have spring brakes.
Usually need a glad hand converter.
Are easier to brake because they are heavier.

Question 30 of 91

1 points

Almost half of all truck driver deaths are the result of:

Speed.
Rollovers.
Following too closely.

Question 31 of 91

1 points

What statement best explains “crack the whip effect”?

When you make a quick lane change or sudden movement with your steering wheel the rear trailer tends to swing out. The force of the rear trailer becomes amplified causing it to roll over (rearward amplification).
Your trailer is half full and the cargo is loaded in the front of the trailer. When you make a sudden steering wheel movement cargo will tend to forcefully slide to the back of the trailer, forcing the trailer to rollover.
When you make a quick lane change or sudden movement with your steering wheel the tractor tends to rock and sway. The velocity of the rear most trailer forces the tractor to rollover before the trailer.

Question 32 of 91

1 points

Which type of truck-trailer combination has the best chance of the “crack the whip” rollover?

A single tractor trailer.
A tractor pulling 3 trailers.
A tractor pulling 2 trailers.

Question 33 of 91

1 points

Which trailers are most likely to get stuck on railroad tracks? (Select three)

Lowboy trailers. A low slung unit.
Possum-belly livestock trailers. A low slung unit.
Tandem axle tractor pulling a flatbed.
Single axle tractors pulling a short trailers. A low slung unit.

Question 34 of 91

1 points

Where should the tractor be when you inspect landing gear after uncoupling the trailer?

With the tractor frame under the trailer.
Completely cleared from the trailer.
With the fifth wheel directly beneath the kingpin.

Question 35 of 91

1 points

Under good driving conditions, you should leave at least one second of space between your vehicle and the vehicle ahead for every _______ feet of your vehicles length.

10
20
30

Question 36 of 91

1 points

The safest way to make turn without entering another traffic lane is:

You should turn wide before you start the turn.
You should turn wide as you complete the turn.
You should not make a turn and move to another place where you can make a turn without crossing other lane.

Question 37 of 91

1 points

In general, the higher your truck’s center of gravity, the:

Easier it is to turn around corners.
More stable it is when turning.
Easier it is to turn over.

Question 38 of 91

1 points

If the service line comes apart while you are driving a combination vehicle but the emergency line stays together, what will happen right away?

The trailer's tank will exhaust through the open line.
The emergency trailer brakes will come on.
Nothing is likely to happen until you try to apply the brakes.

Question 39 of 91

1 points

Glad hands are used to connect the:

Electric lines from the tractor to trailer.
Kingpin from the trailer to the locking jaws of the fifth wheel.
Service and emergency air lines from the truck to the trailer.

Question 40 of 91

1 points

A driver crosses the air lines when hooking up to an old trailer. What will happen?

The hand valve will apply the tractor brakes instead of the trailer brakes.
If the trailer has no spring brakes, you could drive away but you wouldn't have trailer brakes.
The brake lights will come on when the brake pedal is pressed.

Question 41 of 91

1 points

The hand valve should be used:

As a parking brake.
Only with a foot brake.
To test the trailer brakes.

Question 42 of 91

1 points

When driving a set of doubles it is necessary to close which shut-off valve in the last trailer.

Front.
Back.
Middle section.

Question 43 of 91

1 points

Your emergency air line breaks or gets pulled apart while you are driving. The loss of pressure will cause the:

Air compressor to unload instead of pumping air.
Emergency trailer brakes to come on.
Trailer supply valve to open.

Question 44 of 91

1 points

How much space should be between upper and lower fifth wheel after coupling?

Just enough to see light through it.
About 1/4 inch.
None.

Question 45 of 91

1 points

If the brakes are not released when you pushed the trailer air supply valve you should:

Check air line connection.
Cross the airlines.
Check electrical cable.

Question 46 of 91

1 points

You have pushed the trailer air supply valve. You should not back a tractor under a trailer until the whole air system is:

At normal pressure.
Empty.
Between 60 and 80 psi.

Question 47 of 91

1 points

You are coupling tractor to a semitrailer. You have connected the airlines. Before backing under the trailer you should:

Supply air to the trailer system, then pull out the air supply knob.
Pull ahead to test the glad hands connections.
Make sure that the trailer brakes are off.

Question 48 of 91

1 points

After you have coupled the trailer you should have to raise the landing gear by using:

Low gear.
Intermediate.
High gear.

Question 49 of 91

1 points

When connecting the glad hands press the two seals with the coupler together at what degree to each other?

45 degree.
90 degree.
180 degree.

Question 50 of 91

1 points

The iron trailer supports are up and the trailer is resting on the tractor. Make sure:

There is enough clearance between the upper and lower fifth wheels.
There is enough clearance between the tractor frame and the landing gears.
The safety latch is in unlocked position.

Question 51 of 91

1 points

When you are uncoupling a loaded trailer lower the landing gear until it:

Reaches the ground.
Makes contact with the ground and leave the trailer off the fifth wheel.
Makes firm contact with the ground.

Question 52 of 91

1 points

When coupling, the proper position of the fifth wheel is:

Level with the ground.
Tilted down toward the end of tractor.
Tilted up toward the end of the tractor.

Question 53 of 91

1 points

Air and electrical lines from the tractor to the trailer should be:

Resting on the frame of the tractor.
Pulled tight with very little slack.
Secured, but with enough slack for turns.

Question 54 of 91

1 points

When backing a tractor under a trailer you should:

Do it quickly to ensure that the kingpin is locked into the fifth wheel.
Always use lowest reverse gear.
Always approach the trailer at a slight angle.

Question 55 of 91

1 points

Compared to a straight truck or bus there are ____ things to inspect in combination vehicles.

Fewer.
The same number.
More.

Question 56 of 91

1 points

You have coupled with a semitrailer. Where should you put the iron trailer supports before driving away?

3 turns off the top with the crank handle secured in it's bracket.
Raised 1/2 way wit the crank handle secured in it's bracket.
Fully raised with the crank handle secured in it's bracket.

Question 57 of 91

1 points

While checking if the trailer is securely coupled to the trailer the landing gears should be:

Fully lowered.
Fully raised.
Slightly raised.

Question 58 of 91

1 points

After you lock the kingpin into the fifth wheel, you should check the connection by pulling:

Forward 50 feet, turning right, and left.
The tractor ahead gently with the trailer brakes locked.
The tractor ahead sharply to release the trailer brakes.

Question 59 of 91

1 points

After the trailer has been coupled to the tractor, the tractor protection control valve should be placed in what position?

Down.
Up.
Normal.

Question 60 of 91

1 points

The tractor protection valve will close and the trailer emergency brakes will come on when there is a major leak in the ____ brake line.

Emergency.
Parking.
Service.

Question 61 of 91

1 points

To unlock the fifth wheel, pull the release handle to the _____ position.

Neutral.
Open.
Closed.

Question 62 of 91

1 points

Off-tracking or cheating causes which of these to follow the wider pass while making a turn?

53-feet bobtail.
Triple towing a 45-feet trailer.
Tractor with two 27-feet trailers.

Question 63 of 91

1 points

To stop a trailer skid you should:

Use the trailer hand brakes.
Countersteer.
Release the brakes.

Question 64 of 91

1 points

When should you use the hand valve to park a combination vehicle?

To park at loading docks.
To park on a grade.
Never.

Question 65 of 91

1 points

When checking the trailer emergency brakes on the tractor protection control valve should be placed in the ____ position?

Emergency.
Normal.
Neutral.

Question 66 of 91

1 points

What gear should the tractor engine be in after you uncouple in the trailer and are inspecting the trailer supports?

Neutral.
Low Reverse.
Hight Reverse.

Question 67 of 91

1 points

You are uncoupling a trailer. After you shut off the trailer air supply and lock the trailer brakes, you should:

Begin to lower trailer landing gear.
Immediately put on your tractor parking brakes.
Back up gently to ease pressure on the fifth wheel locking jaws.

Question 68 of 91

1 points

Combination vehicles are usually heavier, longer, and require more driving skill than single commercial vehicles.

True
False

Question 69 of 91

1 points

More than half of truck driver deaths in crashes are the result of rollovers. Trucks turn over easier when fully loaded and are:

Two times more likely to rollover in a crash than empty rigs.
Five times more likely to rollover in a crash than empty rigs.
Ten times more likely to rollover in a crash than empty rigs.

Question 70 of 91

1 points

When you turn suddenly while pulling doubles, which trailer is most likely to turn over?

The rear trailer is twice as likely to turn over as the tractor.
The front trailer is twice as likely to turn over as the tractor.
Each trailer is equally likely to turn over as the tractor.

Question 71 of 91

1 points

Why should you not use the trailer hand brake to straighten out a jackknifing trailer?

Because the brake handle is too hard to reach.
Because the brakes on the trailer wheels cause the skid in the first place.
Because the brakes on the trailer wheels will not respond to the hand brake.

Question 72 of 91

1 points

What is a tractor jackknife?

When you lock up the drive tires on the trailer and the trailer spins out sideways as the tractor continues to push forward.
When you lock up the drive tires on the tractor and the tractor spins out sideways as the trailer continues to push forward.
Neither of these answers are correct.

Question 73 of 91

1 points

You should swing wide to the left before starting a 90 degree turn to the right?

Yes
No

Question 74 of 91

1 points

Why should you not use the trailer hand valve while driving?

Because it won't work as well as the foot brake.
Because you should use the parking brake.
Because of the danger of making the trailer skid.

Question 75 of 91

1 points

Describe what the trailer air supply control does:

It is used to supply the trailer with air, shut the air off, and put on the trailer emergency brakes.
It is a yellow, six sided knob used to control the tractor protection valve.
It is a device used to keep the trailer behind the tractor.

Question 76 of 91

1 points

Describe what the service line is for?

To carry air to the parking brake to control the trailer brakes.
To carry air to a relay valve that allows the trailer brakes to be applied quickly.
To carry air to the cab of the rig to cool it.

Question 77 of 91

1 points

What are the other names for the Service Air Line?

Control line or signal line.
Straight line or control line.
Curved line or signal line.

Question 78 of 91

1 points

What is the emergency air line?

Air lines connecting the parking brake to the trailer brakes.
Air lines that control the emergency brakes of the tractor.
Air lines that control the emergency brakes on combination vehicles.

Question 79 of 91

1 points

What is the emergency air line for?

To engage the front brakes of the tractor in case of an emergency.
To engage the trailer brakes in case of air pressure loss.
To have extra air pressure in case you need it.

Question 80 of 91

1 points

Why should you use chocks when parking a trailer without spring brakes?

Because you don't want the trailer rolling down a hill.
Because if the air pressure leaks away or down, there will be no brakes.
Because some states require chocking of trailer wheels.

Question 81 of 91

1 points

When a vehicle is carrying a load at night, which extends four feet or more beyond the rear of the body, there must be __ at the extreme end of the load.

2 Red lights.
1 Red flag.
2 Red flags.

Question 82 of 91

1 points

How long does it take a typical tractor trailer to clear a single track? A double track?

It takes 10 seconds to clear a single track, and more than 12 seconds to clear a double track.
It takes 7 seconds to clear a single track, and more than 10 seconds to clear a double track.
It takes 14 seconds to clear a single track, and more than 15 seconds to clear a double track.

Question 83 of 91

1 points

You have pushed in the trailer supply valve. You should not move the tractor until the whole air system:

Empty.
At normal pressure.
Between 60 and 80 psi.

Question 84 of 91

1 points

The best way to tell if your trailer has started to skid is to:

Hear the wheels skidding.
See it in your mirrors.
Feel for "pulling" in the cab.

Question 85 of 91

1 points

Which of these vehicles off-track the most?

5-axle tractor towing a 52-foot trailer.
5-axle tractor towing a 45-foot trailer.
5-axle tractor towing a 42-foot trailer.

Question 86 of 91

1 points

A tractor with a(n) ____ trailer requires the shortest amount of stopping distance.

Empty.
Lightly loaded.
Fully Loaded.

Question 87 of 91

1 points

A trailer is most likely to jackknife when it is:

Loaded to full capacity.
Overloaded.
Empty.

Question 88 of 91

1 points

If you have coupled with a semitrailer, where should the front trailer supports be before driving away?

Raised 1/2 way with the crank handle secured in it's bracket.
Raised 3/4 way with the crank handle removed.
Fully raised with the crank handle secured in it's bracket.

Question 89 of 91

1 points

The fifth wheel locking lever is not locked after the jaws close around the kingpin. This means that:

The trailer will not swivel on the fifth wheel.
The parking lock is off and may drive away.
The coupling is not right and should be fixed before driving the coupled unit.

Question 90 of 91

1 points

You want to inspect the trailer supports. You should place the tractor transmission in which gear after you have uncoupled the trailer?

Low reverse.
Neutral.
High reverse.

Question 91 of 91

1 points

When should you use chocks to park a trailer not equipped with spring brakes?

Never.
Always.
Only when it will be parked on an incline.

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