Combination Vehicles CDL Practice Test

Why are combination vehicles harder to drive than single units?

• A. They have more pivot points, are longer, and have rearward amplification
• B. They have stronger engines
• C. They have more brakes
• D. They are taller

Rearward amplification (the "crack-the-whip" effect) is greater in:

• A. Doubles and triples
• B. Single tractor-trailers
• C. Straight trucks
• D. Buses

When a trailer skid occurs, the recommended action is:

• A. Release the brakes to allow trailer wheels to roll, countersteer if needed
• B. Brake harder
• C. Apply parking brake
• D. Steer in direction of skid only

What is "trailer jackknife"?

• A. Trailer swings out of line with the tractor, often forming a near-90° angle
• B. Tractor leaves the road
• C. Trailer separates from tractor
• D. Tires blow out

When coupling, the fifth wheel jaws should:

• A. Lock around the kingpin completely with the safety latch closed
• B. Touch but not lock
• C. Be left open
• D. Be greased only

Before coupling, you should check that:

• A. Fifth wheel is properly greased and tilted slightly down at rear
• B. Fifth wheel is dry
• C. Fifth wheel is tilted up
• D. Fifth wheel is removed

When backing under a trailer, you should:

• A. Back slowly until the kingpin is captured
• B. Back fast
• C. Stop short and lift trailer
• D. Back without the parking brake

How do you test that the fifth wheel is locked?

• A. With trailer brakes set, pull forward gently in low gear
• B. Bounce the trailer
• C. Push the kingpin
• D. Visual only

When uncoupling, lower the landing gear so:

• A. It just touches the ground, then crank a few more turns
• B. It supports full weight
• C. Wheels lift
• D. Landing gear holds the kingpin

What is "off-tracking" in combination vehicles?

• A. Rear trailer wheels follow a path inside the front wheels in turns
• B. Trailer leaves the road
• C. Tractor follows trailer
• D. Wheels rotate at different speeds

When passing a curve, longer combinations may need to:

• A. Use part of the next lane to keep trailer on the road
• B. Stay strictly in lane
• C. Stop in the curve
• D. Speed up

Antilock braking systems on combinations help by:

• A. Preventing wheel lockup so steering and stability are retained
• B. Stopping faster always
• C. Reducing fuel use
• D. Eliminating need for inspection

How do you adjust your driving when towing an empty trailer?

• A. Increase following distance — empty trailers are easier to skid
• B. Drive faster
• C. Use only trailer brake
• D. Increase speed in turns

What does the term "bobtail tractor" mean?

• A. Tractor without a trailer
• B. Tractor with two trailers
• C. Tractor with a sleeper berth
• D. Tractor with a refrigerated trailer

Which of these is true about coupling air lines?

• A. Service line glad hand to service, emergency to emergency, locked properly
• B. Either order
• C. Only emergency required
• D. Service only

Why should you check trailer tires more carefully on combinations?

• A. Trailer tires are often older, worn, and more numerous
• B. They are larger
• C. They are heated
• D. They are filled with nitrogen

How can you tell that the height of the trailer is right for coupling?

• A. It is just low enough that the tractor will lift it slightly when backed under
• B. Trailer must be higher than fifth wheel
• C. Trailer must be much lower
• D. Height does not matter

What can you do to help prevent trailer jackknife?

• A. Slow before turns, avoid hard braking on slippery surfaces
• B. Use trailer brakes only
• C. Use parking brake to slow
• D. Speed up in turns

When pulling triples, the third (rear) trailer:

• A. Has the most rearward amplification — most likely to roll over
• B. Has the least sway
• C. Has stronger brakes
• D. Has wider tires

Which of these is the most dangerous on a combination vehicle?

• A. Quick lane changes — they amplify trailer sway
• B. Slow turns
• C. Constant speed
• D. Light braking

When emergency situations require braking, on a combination vehicle without ABS use:

• A. Controlled or stab braking
• B. Brake hand valve only
• C. Parking brake
• D. Engine brake only

What is the maximum gross combination weight rating (GCWR) for a Class A CDL?

• A. 26,001 lbs or more with towed unit over 10,000 lbs
• B. 20,000 lbs
• C. 10,000 lbs
• D. 40,000 lbs

When backing a trailer, turn the steering wheel:

• A. In the direction opposite of where you want the trailer rear to go
• B. Same as where trailer should go
• C. Straight always
• D. Right always

When backing in a straight line, correct drift by:

• A. Small steering inputs and/or pulling forward to reset
• B. Braking hard
• C. Speeding up
• D. Cranking wheel hard over

Why is securement in combinations critical?

• A. Cargo shifting can affect handling, brake balance, and rollover risk
• B. It is a federal-only issue
• C. Only at scales
• D. Only on long trips

What is the purpose of safety chains on a converter dolly?

• A. Hold the dolly to the trailer if the pintle hook fails
• B. Keep dolly aligned
• C. Tow extra cargo
• D. Decoration

When pulling a refrigerated trailer, the reefer fuel is checked:

• A. Before each trip and during long trips
• B. Only at the start
• C. Only at destination
• D. Never

What is "dock walk"?

• A. Trailer wheels creep away from the dock as workers load — apply parking brakes and chock
• B. Driver waiting at dock
• C. Walking under trailer
• D. Inspector walk-around

When you are driving a combination on a wet road, you should:

• A. Reduce speed by about a third
• B. Drive normal speed
• C. Speed up to throw water off tires
• D. Use only the trailer brakes

Why should you never use the trailer hand valve in driving?

• A. Using only trailer brakes can cause skid/jackknife
• B. It overloads the engine
• C. It uses fuel
• D. It wears tires

Which one of these brake systems applies and releases the brakes when the driver uses the brake pedal?

• A. Service brake
• B. Parking brake
• C. Emergency brake
• D. Spring brake

Which of the following is the proper procedure for connecting the air lines?

• A. Check seals, lock glad hands, supply red, service blue
• B. Service first
• C. No locking required
• D. Either side either color

Which is true about coupling triples?

• A. Couple front trailer to tractor first, then add subsequent trailers using converter dollies
• B. Couple back to front
• C. Couple all at once
• D. Couple any order

What is a "converter dolly"?

• A. Single axle with a fifth wheel that converts a semitrailer into a full trailer
• B. A repair tool
• C. A refrigeration unit
• D. A spare wheel

Pintle hooks should be checked for:

• A. Proper engagement, locks, and secondary safety devices
• B. Color
• C. Brand
• D. Air pressure

Why should you avoid backing a combination if possible?

• A. Backing combinations is one of the most dangerous maneuvers
• B. It uses fuel
• C. It is illegal
• D. It damages tires

Why use a helper when backing?

• A. To watch blind spots and signal you
• B. To drive
• C. To set the parking brake
• D. To open doors

How do you avoid trailer skids?

• A. Drive smoothly, avoid hard braking, slow before curves
• B. Brake early hard
• C. Use trailer brake only
• D. Disable ABS

When the trailer ABS warning light is on, you should:

• A. Treat trailer brakes as conventional, plan for repair
• B. Not drive
• C. Drive only at night
• D. Disconnect trailer

What is the trailer hand valve typically used for?

• A. Testing trailer brakes — never as parking brake or to stop alone
• B. Parking
• C. Normal stops
• D. Backing

Which of the following is true about coupling/uncoupling on a slope?

• A. Avoid if possible — chock wheels and use parking brakes
• B. Park brake not needed
• C. Shift to neutral
• D. Drag the trailer

What does it mean if the kingpin pops up after coupling?

• A. Trailer is not properly engaged — recouple
• B. Coupling complete
• C. Brake check needed
• D. Air pressure low

What air pressure should you have before driving a combination?

• A. At least 100 psi
• B. 60 psi
• C. 20 psi
• D. 150 psi

How can you test the trailer service brakes?

• A. Pull at 5 mph and apply trailer hand valve gently
• B. Slam foot brake
• C. Drag trailer
• D. Use parking brake

What can cause a trailer to swing wide on a turn?

• A. Off-tracking — rear wheels follow inside path
• B. Engine torque
• C. Speed too high
• D. High tire pressure

What should you do if the trailer starts swaying?

• A. Slow down by easing off accelerator without brakes
• B. Brake hard
• C. Steer sharply
• D. Speed up

What can cause coupling problems with the fifth wheel?

• A. Loose mounting bolts, broken or worn parts, improper greasing
• B. Cold weather only
• C. Hot weather only
• D. Slope only

Why must trailer landing gear be fully retracted before driving?

• A. It can drag, hit obstacles, or cause damage
• B. It saves fuel
• C. It is for looks
• D. It must be partially down

When uncoupling, after lowering the landing gear, the next step is:

• A. Disconnect air lines and electrical, secure them, then release fifth wheel
• B. Pull away immediately
• C. Set the brake only
• D. Disconnect kingpin manually

Why drive the tractor only halfway out from under the trailer first?

• A. Confirms landing gear can hold the trailer
• B. Stretches the air lines
• C. Tests the brakes
• D. Resets the fifth wheel

What does "tracking" mean for combinations?

• A. How well the trailer follows the tractor through a turn
• B. Speed of trailer
• C. Tire wear pattern
• D. GPS position

When pulling out of the driving lane to make a wide right turn, you risk:

• A. Other drivers passing on the right and being squeezed
• B. Hitting the curb
• C. Engine stall
• D. Trailer separation

What is the danger of a trailer rolling over?

• A. Higher center of gravity than truck — can roll easily, especially with liquid loads
• B. Trailer weighs less
• C. Trailer cannot roll
• D. Only on snow

Inspecting the upper coupler involves checking:

• A. Kingpin and fifth-wheel plate for cracks and proper mounting
• B. Tire pressure
• C. Headlights
• D. Engine oil

How often should fifth wheels be greased?

• A. Per manufacturer schedule, typically each lubrication cycle
• B. Yearly only
• C. Never
• D. Daily

What is the function of a slider on a fifth wheel?

• A. Allows weight redistribution by sliding the fifth wheel forward or back
• B. Steers the trailer
• C. Brake assist
• D. Shock absorption

What is the function of the safety chains?

• A. Backup retention if pintle hook fails on a dolly
• B. Decorative only
• C. For chocking
• D. For tow truck

Why position your tractor in front of the trailer before backing under?

• A. Square alignment makes coupling and prevents missed kingpin
• B. Faster backing
• C. Saves fuel
• D. Required by law

Why do you put on the parking brake of the tractor when uncoupling?

• A. Prevents tractor rollaway during uncoupling
• B. Saves fuel
• C. Cools the engine
• D. Charges batteries

When backing into a parking spot, the safest approach is:

• A. Driver-side back so you can see the rear of the trailer
• B. Blind-side back
• C. Straight back without help
• D. No mirrors needed

What is a "pup" trailer?

• A. A short trailer used in doubles, often 26-29 ft
• B. A puppy
• C. A tractor
• D. A trailer dolly

When pulling doubles, place the heaviest trailer:

• A. Behind the tractor (lead position)
• B. Behind the second trailer
• C. Either
• D. Always lighter first

When inspecting a converter dolly, check the:

• A. Pintle hook, safety chains, fifth wheel, air and electrical lines
• B. Engine
• C. Air conditioner
• D. Sleeper

How can you tell that the second trailer is properly coupled to the dolly?

• A. Pull test, visual check, inspect kingpin engagement
• B. Visual only
• C. Sound only
• D. Bouncing

What is the safest way to disconnect a converter dolly?

• A. Lower trailer landing gear, disconnect dolly air/electric, unlock fifth wheel, pull dolly out
• B. Pull dolly first
• C. Drag dolly out
• D. Disconnect lines only