Class A · Combination Vehicles
Combination Vehicles practice test
20 free questions to answer on this page, each with its explanation and the manual section. The app has all 150, with exam mode and a mistakes list.
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Question 1 of 20 · Section 6.1
Your load sits to one side and makes the trailer lean. What does that do?
Answer: D, Makes a rollover more likely
A trailer that leans because the load is off to one side tips over more easily. Center the cargo and spread it out as much as you can.
Combination Vehicles · Section 6.1.1 · California CDL Handbook
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Question 2 of 20 · Section 6.1
In the rearward amplification chart, what does a value of 2.0 mean?
Answer: D, The rear trailer tips over twice as easily as the tractor
Rearward amplification compares the last trailer with the tractor in a quick lane change; 2.0 means the trailer is twice as likely to go over.
Combination Vehicles · Section 6.1.2 · California CDL Handbook
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Question 3 of 20 · Section 6.1
Which usually takes longer to stop: a combination vehicle that is empty or one that is fully loaded?
Answer: D, The empty one, because it has poorer traction
When lightly loaded, the stiff springs and strong brakes give poor traction, so the wheels lock up easily. Bobtail tractors can also be hard to stop smoothly.
Combination Vehicles · Section 6.1.3 · California CDL Handbook
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Question 4 of 20 · Section 6.1
Which rig is most likely to get stuck on a raised railroad crossing?
Answer: B, A lowboy or car carrier
Low-slung units such as lowboys, car carriers, moving vans, and possum-belly livestock trailers can hang up on raised crossings.
Combination Vehicles · Section 6.1.4 · California CDL Handbook
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Question 5 of 20 · Section 6.1
When is a trailer jackknife most likely?
Answer: C, When the trailer is empty or lightly loaded
Locked trailer wheels make the trailer swing around, and this is more likely when it is empty or lightly loaded.
Combination Vehicles · Section 6.1.5 · California CDL Handbook
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Question 6 of 20 · Section 6.2
The trailer hand valve is known by which other names?
Answer: A, The trolley valve or Johnson bar
The hand valve, which some drivers call the trolley valve or Johnson bar, works only the trailer brakes and should be used only to test them.
Combination Vehicles · Section 6.2.1 · California CDL Handbook
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Question 7 of 20 · Section 6.2
What is true of tractor protection valve controls on some older vehicles?
Answer: C, They may not work automatically
Older vehicles may have a lever instead of a knob, and their tractor protection valve controls may not operate automatically.
Combination Vehicles · Section 6.2.3 · California CDL Handbook
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Question 8 of 20 · Section 6.2
How do you connect two glad hands?
Answer: B, Seals together at a 90-degree angle, then turn to lock
Clean the couplers and seals first, press the seals together with the couplers at a 90-degree angle, and give the glad hand a turn to join and lock them.
Combination Vehicles · Section 6.2.5 · California CDL Handbook
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Question 9 of 20 · Section 6.2
What fills the trailer air tanks?
Answer: D, The emergency (supply) line from the tractor
Each trailer and converter dolly has its own air tanks, filled by the emergency line, and relay valves send that air to the trailer brakes.
Combination Vehicles · Section 6.2.6 · California CDL Handbook
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Question 10 of 20 · Section 6.2
Which trailers are not required to have spring brakes?
Answer: D, Dollies and trailers built before 1975
Newer trailers have spring brakes, but converter dollies and trailers built before 1975 do not have to. Those use emergency brakes that work from trailer tank air.
Combination Vehicles · Section 6.2.8 · California CDL Handbook
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Question 11 of 20 · Section 6.3
How does ABS keep a trailer's wheels from locking?
Answer: B, It senses lockup coming and lowers brake pressure
The computer senses that a wheel is about to lock, reduces the braking pressure to a safe level, and helps you keep control.
Combination Vehicles · Section 6.3.2 · California CDL Handbook
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Question 12 of 20 · Section 6.4
Why should you learn the coupling details for the specific rig you drive?
Answer: B, The steps differ between rigs
The general coupling steps apply to most rigs, but they differ in detail, so learn the procedure for the trucks you will drive.
Combination Vehicles · Section 6.4 · California CDL Handbook
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Question 13 of 20 · Section 6.4
Which reverse gear should you use when backing the tractor under the trailer?
Answer: C, The lowest reverse gear
Back under slowly in the lowest reverse gear so you do not hit the kingpin too hard, and stop when it locks into the fifth wheel.
Combination Vehicles · Section 6.4.1 · California CDL Handbook
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Question 14 of 20 · Section 6.4
After plugging the electrical cord into the trailer, what should you do?
Answer: C, Fasten the safety catch
Plug in the cord, fasten its safety catch, and check that the air and electrical lines are undamaged and clear of moving parts.
Combination Vehicles · Section 6.4.1 · California CDL Handbook
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Question 15 of 20 · Section 6.4
You are uncoupling a loaded trailer. What do you do after the landing gear touches the ground firmly?
Answer: C, Turn the crank a few extra turns in low gear
A few extra turns lift some weight off the tractor, which makes it easier to unlatch the fifth wheel and to couple next time. Do not lift the trailer off the fifth wheel.
Combination Vehicles · Section 6.4.2 · California CDL Handbook
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Question 16 of 20 · Section 6.4
Before uncoupling, what must the parking surface be able to do?
Answer: D, Support the weight of the trailer
Make sure the parking area can hold up the trailer, and line the tractor up with it.
Combination Vehicles · Section 6.4.2 · California CDL Handbook
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Question 17 of 20 · Section 6.4
When uncoupling, how do you ease the pressure on the fifth-wheel locking jaws?
Answer: D, Back up gently and set the parking brakes there
Lock the trailer brakes, back gently against the kingpin, and set the parking brakes there. With pressure off the jaws, the release lever is easier to pull.
Combination Vehicles · Section 6.4.2 · California CDL Handbook
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Question 18 of 20 · Section 6.4
How can you tell a pintle hook latch is correctly locked?
Answer: B, The lock handle is flush with the top of the latch
When the latch is pushed closed and locked, the lock handle rotates up until it is flush with the top of the latch. Then insert the tethered lock pin.
Combination Vehicles · Section 6.4.3 · California CDL Handbook
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Question 19 of 20 · Section 6.5
Why must a sliding fifth wheel not be too far forward?
Answer: A, The frame could hit the landing gear or the cab hit the trailer in turns
Check that the sliding fifth wheel is far enough back that the tractor frame clears the landing gear and the cab clears the trailer during turns.
Combination Vehicles · Section 6.5.1 · California CDL Handbook
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Question 20 of 20 · Section 6.5
What should you check on the air and electric lines to the trailer?
Answer: A, That they are secure, leak-free, and slack enough for turns
The cord must be firmly plugged in, the air lines properly connected to the glad hands without leaks, and all lines secured with enough slack for turns.
Combination Vehicles · Section 6.5.1 · California CDL Handbook
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The full bank is in the app
All 150 Combination Vehicles questions, an exam mode with 20 questions and the 80% pass mark, explanations for every answer, and a mistakes list that keeps what you missed until you clear it.
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What the Combination Vehicles test covers
Section 6 of the CDL manual: driving a tractor-trailer or a truck with a trailer, the trailer's air brakes, coupling and uncoupling, and the inspection. You take this test to drive combination vehicles (Section 1.1.1). The section numbers are the same in the California, Texas and Florida handbooks.