Louisiana Combination Vehicles CDL Practice Test

This is a free 20-question practice test for the Combination Vehicles portion of the Louisiana Commercial Driver's License knowledge exam. Questions are pulled from a pool of 55 drawn from the AAMVA CDL Manual, which is the source document the Louisiana Office of Motor Vehicles uses to write its actual exam.

How it works: Click an answer. The correct choice highlights in green, and you'll see a short explanation. Aim for 85% or better before you sit for the real test in Louisiana.

Question 1 of 20

A "trailer skid" happens when:

Trailer wheels lose traction and the trailer slides outward
Tractor wheels lock
Brakes overheat
Cargo shifts

Correct. When trailer wheels lose traction (often from over-application of trailer brakes alone), the trailer can slide sideways — a trailer skid or trailer swing.

Question 2 of 20

Your trailer ABS warning lamp is on. The trailer service brakes:

Will not work at all
Still work normally — only ABS function is unavailable
Lock up
Apply automatically

Correct. Trailer service brakes still work normally without ABS. Have the system repaired; ABS gives extra control during emergency braking.

Question 3 of 20

Most jackknifes happen because:

Drive wheels skid during braking on slippery surfaces
Brakes work too well
The road is dry
Cargo is too light

Correct. Loss of traction on the tractor drive axles during braking — typically on slick surfaces or with overly aggressive braking — causes a jackknife.

Question 4 of 20

On a slippery surface, drive in:

Higher gears at higher RPM
A gear that minimizes torque to the drive wheels and brake earlier and gentler
The lowest gear
Whatever is fastest

Correct. Reduce engine power to drive wheels (higher gear, gentler accelerator) and brake earlier and gentler to avoid wheel spin or skid.

Question 5 of 20

When you cross railroad tracks in a tractor-trailer, you should:

Shift gears to maintain speed
Cross in a single gear without shifting, and never start across without room to clear the rails
Stop on the tracks if the light turns red
Honk repeatedly

Correct. Crossing in one gear (without shifting) prevents stalling on the tracks. Never enter a crossing unless you can clear it without stopping.

Question 6 of 20

When making a U-turn, a tractor-trailer needs:

Less space than a car
Substantially more space than a car — often more than a single intersection allows
The same space as a car
No turning space

Correct. Tractor-trailer turning radius is much larger than a car. A standard intersection rarely allows a U-turn — find a wider turning area.

Question 7 of 20

When you turn on a tight radius (e.g., into a tight loading dock):

Off-tracking is exaggerated; the trailer will swing far inside the line of the tractor wheels
Off-tracking disappears
Trailer follows tractor exactly
Trailer goes wide

Correct. On a tight radius, off-tracking is more pronounced. Sweep wide enough that the trailer wheels clear curbs and obstacles.

Question 8 of 20

Trailer wheels off-track:

Outside the path of the tractor wheels
Inside (tighter turn radius) than the tractor wheels
At the same path as the tractor wheels
Cannot be predicted

Correct. Trailer wheels follow a tighter path than tractor wheels through a turn — off-tracking. Plan turns to keep trailer tires on the pavement and clear of curbs.

Question 9 of 20

To make a trailer go where you want when backing, the steering wheel should:

Be turned in the direction you want the trailer to go
Be turned opposite to the direction you want the trailer to go (then corrected)
Stay still
Be held lightly

Correct. Backing is opposite-direction steering: to swing the trailer right, turn the wheel left first, then correct as the trailer follows.

Question 10 of 20

A sliding-tandem trailer allows you to:

Adjust the trailer-axle position to redistribute weight between trailer axles and tractor drive axles
Speed up
Cool the load
Steer the trailer

Correct. Sliding tandems shift trailer axles forward (more weight on tractor) or aft (more weight on trailer axles), helping meet axle-weight limits.

Question 11 of 20

A combination vehicle on slippery roads should be driven:

Faster to maintain control
Slower with greater following distance
At normal speed
In a higher gear

Correct. Reduce speed by at least one third on wet roads and one half on snow; double following distance on slick surfaces.

Question 12 of 20

A combination-vehicle pre-trip should include:

All single-vehicle items plus fifth wheel, kingpin, sliding fifth wheel/sliding tandem locks, mud flaps, trailer brakes, lights, and trailer tires
Only the tractor
Only the trailer
Only the cargo

Correct. You inspect the entire rig — tractor + trailer + connections + cargo securement — not just the tractor.

Question 13 of 20

When you "G.O.A.L." in trucking, you:

Get Off And Look — visually verify the area before backing
Go Over A Limit
Grab On And Lift
Greet Other Approaching Loaders

Correct. G.O.A.L. — Get Out And Look — is the universal driver-school rule before any tight backing maneuver.

Question 14 of 20

When making a turn, you should signal:

Just before the turn
Well in advance — at least 100 feet for a turn at low speed
Only if other vehicles are present
At the start of the turn

Correct. Signal early enough that other drivers see and process the signal — generally at least 100 feet before in town, longer at highway speeds.

Question 15 of 20

When you supply air to the trailer for the first time after coupling, you should:

Wait until air pressure builds in the trailer reservoir, then test the trailer brakes by pulling out the trailer-supply knob
Drive away immediately
Disconnect the lines
Skip the test

Correct. Charge the trailer system. Then test the trailer brake function by tugging gently or pulling the trailer-supply knob to confirm trailer brakes apply.

Question 16 of 20

Combination vehicles are usually:

Easier to drive than single trucks
Harder to drive than single trucks because of length, weight, and the unique handling of articulated vehicles
The same as single trucks
Faster than single trucks

Correct. Combination vehicles (tractor-trailer rigs) are heavier, longer, and articulate at the fifth wheel — all making them more demanding than single-unit trucks.

Question 17 of 20

Maximum allowable trailer-brake leakage rate (engine off, brakes released, combination vehicle) is:

1 psi/min
3 psi/min
5 psi/min
7 psi/min

Correct. Combination vehicles: no more than 3 psi/min with brakes released, 4 psi/min with brakes applied.

Question 18 of 20

The most likely cause of a tractor jackknife is:

Light cargo
Drive wheels lock during braking
Slow speed
Loose load

Correct. When drive wheels lose traction (locked, oversteer, ice), the tractor pivots ahead of the trailer — a jackknife.

Question 19 of 20

A combination vehicle requires more time to stop than a single vehicle because:

It is much heavier and air must travel further to reach the trailer brakes
It accelerates faster
It is shorter
Drivers wait longer

Correct. Greater weight + brake-lag in long air lines = longer stopping distance. Plan ahead.

Question 20 of 20

A sliding fifth wheel allows you to:

Adjust the weight distribution between drive axles and trailer axles
Speed up
Slow down
Disable the trailer brakes

Correct. Sliding fifth wheels move forward to put more weight on drive axles or aft to reduce drive-axle weight, helping comply with axle-weight limits.

About the Louisiana Combination Vehicles exam

Most states administer 20 Combination Vehicles questions and require 80% to pass. The exam emphasizes the unique handling of articulated vehicles: how trailers track behind the tractor, how to prevent rollover, how to manage rearward amplification with multi-trailer combinations, and the correct sequence to couple and uncouple.

The Louisiana Office of Motor Vehicles follows the federal CDL standards established by FMCSA. To earn the Combination Vehicles credential, you must answer at least 80% of the questions correctly. Many candidates score lower the first time because the test pulls from a large pool — refreshing this page will give you a different mix of questions, drawn from the same authoritative source.

Want more practice? Try the full Combination Vehicles question bank or browse all Louisiana CDL practice tests.