25 realistic Combination Vehicles practice questions for Florida CDL applicants. Required for: Class A CDL (tractor-trailer combinations). Official test: 20 questions, 16 correct to pass.
Question 1 of 25 · Vehicle Dynamics
Why should you avoid sudden steering and braking with combinations?
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A.
It wears tires faster
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B.
It can cause jackknife or rollover
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C.
It uses more fuel
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D.
It scares passengers
Correct answer: B.
Sudden inputs can break traction and lead to jackknifing or rollovers.
Question 2 of 25 · Inspection
When checking the trailer air supply, you should:
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A.
Charge the trailer with air, then disconnect the supply hose to test trailer emergency brakes
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B.
Pump the brakes
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C.
Disconnect the trailer power cord
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D.
Open the trailer service line manually
Correct answer: A.
Disconnecting the supply line tests that the trailer emergency brakes apply automatically.
Question 3 of 25 · Vehicle Dynamics
When you turn suddenly with a high center of gravity, the trailer can:
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A.
Roll over
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B.
Stop more quickly
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C.
Track better
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D.
Reduce fuel use
Correct answer: A.
High centers of gravity make trailers prone to rollover during sharp turns.
Question 4 of 25 · Vehicle Dynamics
Empty trucks have what kind of stopping distance compared to fully loaded ones?
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A.
Shorter
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B.
Same
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C.
Longer
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D.
Half
Correct answer: C.
Empty rigs have less traction on drive axles and require greater stopping distance.
Question 5 of 25 · CDL Rules
Which is true about long combination vehicles (LCVs)?
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A.
They are easier to maneuver in tight spaces
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B.
They require additional driver training and special permits
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C.
They handle the same as single trailers
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D.
They never require special routes
Correct answer: B.
LCVs need extra training, certifications, and often follow restricted routes.
Question 6 of 25 · Coupling
What is the fifth wheel?
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A.
A spare wheel
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B.
A coupling device that connects the tractor to the trailer
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C.
A device on the trailer to support cargo
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D.
A type of axle
Correct answer: B.
The fifth wheel is the round, plate-shaped coupling that connects the tractor to the trailer.
Question 7 of 25 · Skids
What can cause a trailer skid in a combination vehicle?
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A.
Locked trailer wheels and over-application of brakes
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B.
Light loads on the trailer
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C.
Tight steering at low speed
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D.
High pressure in steering tires
Correct answer: A.
Locked trailer wheels cause trailer skid; reduce brake pressure to recover.
Question 8 of 25 · Inspection
You should inspect the rear of the trailer for:
-
A.
Cracked or missing lights
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B.
Lights and reflectors are clean and operational
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C.
Mud flap condition
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D.
All of the above
Correct answer: D.
Check lights, reflectors, mud flaps, and license plate during pre-trip.
Question 9 of 25 · Coupling
When coupling, what should you do after the fifth wheel locks onto the kingpin?
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A.
Pull the tractor forward gently to make sure the kingpin is locked
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B.
Disconnect the air lines
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C.
Drive away immediately
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D.
Release the trailer parking brake first
Correct answer: A.
Tug-test by gently pulling forward with the trailer brakes set to confirm the lock.
Question 10 of 25 · Skids
What is the result of a "trailer jackknife"?
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A.
Trailer continues straight ahead
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B.
Trailer swings out and tractor pivots
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C.
Trailer comes to a quick safe stop
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D.
Trailer disengages
Correct answer: B.
In a trailer jackknife, the trailer swings out, often into adjacent lanes.
Question 11 of 25 · Coupling
What is the kingpin?
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A.
A pin in the engine
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B.
A vertical pin on the front of the trailer that locks into the fifth wheel
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C.
A part of the air brake system
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D.
A type of warning device
Correct answer: B.
The kingpin slides into the fifth wheel jaws to lock the trailer to the tractor.
Question 12 of 25 · Inspection
When should you check trailer brakes during operation?
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A.
First few miles after coupling
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B.
Every fuel stop
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C.
Just at the end of the trip
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D.
Never during the trip
Correct answer: A.
Test trailer brakes early in the trip to make sure they are functioning correctly.
Question 13 of 25 · Combination Air
Trailer hand valve is used to:
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A.
Test trailer brakes
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B.
Park the trailer
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C.
Bypass the foot valve
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D.
Drain trailer tanks
Correct answer: A.
Use the trailer hand valve only for testing — not for parking or normal stops.
Question 14 of 25 · Backing
Which is correct about backing a tractor-trailer?
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A.
Steer in the same direction you want the trailer to go
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B.
Steer in the opposite direction you want the trailer to go
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C.
Use the throttle to back
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D.
Back as fast as possible
Correct answer: B.
When backing, turn the steering wheel opposite to the direction you want the trailer to move.
Question 15 of 25 · Skids
Tractor jackknife occurs when:
-
A.
Drive wheels lose traction and skid
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B.
The trailer wheels lock
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C.
The trailer slides forward
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D.
Steering wheels lock
Correct answer: A.
Drive wheels skidding cause tractor jackknife; trailer wheels skidding cause trailer jackknife.
Question 16 of 25 · Vehicle Dynamics
What is "off-tracking"?
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A.
When the rear wheels follow a different path than the front wheels
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B.
When the trailer slides off the road
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C.
When the trailer is improperly loaded
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D.
A type of fifth wheel
Correct answer: A.
In turns, rear wheels travel a smaller arc than the front, causing off-tracking.
Question 17 of 25 · Coupling
When uncoupling, you should:
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A.
Lower the landing gear before pulling the kingpin release
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B.
Lift the trailer with the fifth wheel
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C.
Release the parking brake
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D.
Rev the engine
Correct answer: A.
Lower the landing gear so the trailer is supported before disconnecting the kingpin.
Question 18 of 25 · Coupling
What does a "low coupling" condition look like?
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A.
Trailer is too high above the fifth wheel
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B.
Trailer is at the right height
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C.
Trailer is too low and tractor frame can hit the trailer
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D.
Trailer is angled to the right
Correct answer: C.
A trailer too low can damage the tractor frame as it slides under it.
Question 19 of 25 · Vehicle Dynamics
Off-tracking is most pronounced in:
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A.
Single vehicles
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B.
Long combinations and curves
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C.
Empty trailers
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D.
Vehicles with disc brakes
Correct answer: B.
Longer wheelbases and tighter curves cause greater off-tracking.
Question 20 of 25 · Inspection
Which is true about gladhand seals?
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A.
They should be replaced if cracked or damaged
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B.
They never need replacement
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C.
They are the same as electrical connections
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D.
They are always made of metal
Correct answer: A.
Replace damaged or worn rubber seals to keep air from leaking at the gladhands.
Question 21 of 25 · Vehicle Dynamics
What's the safest way to handle a tight turn with a long combination?
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A.
Take it wide using both lanes if necessary
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B.
Drive as fast as possible to maintain momentum
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C.
Use the trailer hand valve
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D.
Make a tight turn
Correct answer: A.
Take wider turns to avoid hitting curbs or other vehicles due to off-tracking.
Question 22 of 25 · Combination Air
When the trailer breaks away or loses air pressure, the trailer brakes should:
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A.
Release
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B.
Apply automatically
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C.
Vibrate
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D.
Disengage
Correct answer: B.
A loss of air should automatically apply the trailer brakes via the emergency system.
Question 23 of 25 · Coupling
Before backing under a trailer, you should:
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A.
Make sure the trailer brakes are set and the trailer is at the correct height
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B.
Disconnect the air lines
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C.
Lower the landing gear
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D.
Engage the parking brake
Correct answer: A.
Confirm trailer brakes are locked and trailer height matches the fifth wheel.
Question 24 of 25 · Coupling
What should you do before connecting air lines?
-
A.
Clean the rubber seals on the glad hands
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B.
Lubricate them with oil
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C.
Replace the seals every trip
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D.
Heat them up
Correct answer: A.
Clean glad hand seals before connecting to ensure a good air seal.
Question 25 of 25 · Coupling
Which is true about pulling away after coupling?
-
A.
Test that the kingpin is locked by gently pulling forward against the trailer brakes
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B.
Pull away as quickly as possible
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C.
Lower the landing gear before pulling away
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D.
Disconnect the air lines first
Correct answer: A.
A pull-test confirms the kingpin is locked before driving away.
About the Combination Vehicles Test
The Combination Vehicles test covers driving combination vehicles safely, combination vehicle air brakes, antilock brake systems, coupling and uncoupling, and inspecting a combination vehicle. Combination vehicles are usually heavier, longer, and require more driving skill than single commercial vehicles. They are also more likely to roll over and jackknife.
The Florida Department of Highway Safety and Motor Vehicles administers this knowledge test as part of its commercial driver license program. To earn the Combination Vehicles on your Florida CDL, you need to score at least 16 out of 20 on the official version.
Topics covered on this practice test
- Coupling: 8 questions
- Vehicle Dynamics: 6 questions
- Inspection: 4 questions
- Skids: 3 questions
- Combination Air: 2 questions
- CDL Rules: 1 question
- Backing: 1 question
How to use this practice test
- Read each question carefully. CDL questions are written precisely — small wording differences matter.
- Click "Show Answers & Explanations" only after answering every question. Don't peek mid-test.
- Read the explanation for every question, even ones you got right. The reasoning is more important than the answer.
- Repeat the test until you score 100%. The questions are deterministic per state, so you can track your improvement over multiple sessions.
- Move on to the other endorsement tests for Florida until you're ready for the official exam.
Tips specific to the Combination Vehicles test
Combination Vehicles questions cover off-tracking, jackknifing, coupling and uncoupling, the fifth wheel, kingpin, glad hands, landing gear, and the special air-brake considerations for tractor-trailer combinations. Expect detailed step-by-step coupling questions.