Question 1 of 20
Your trailer ABS warning lamp is on. The trailer service brakes:
Correct. Trailer service brakes still work normally without ABS. Have the system repaired; ABS gives extra control during emergency braking.
Alabama Combination Vehicles CDL Practice Test
This is a free 20-question practice test for the Combination Vehicles portion of the Alabama 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 Alabama Law Enforcement Agency Driver License Division 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 Alabama.
Question 2 of 20
A combination vehicle requires more time to stop than a single vehicle because:
Correct. Greater weight + brake-lag in long air lines = longer stopping distance. Plan ahead.
Question 3 of 20
A jackknife happens when:
Correct. Jackknife is when the drive wheels skid and the trailer continues forward, causing the tractor to pivot — the rig folds at the fifth wheel like a closing knife.
Question 4 of 20
During a pre-trip inspection, you should also check that the cargo:
Correct. Cargo securement, weight balance, and size compliance are all driver responsibilities — check before each trip.
Question 5 of 20
Trailer wheels off-track:
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 6 of 20
A combination vehicle on slippery roads should be driven:
Correct. Reduce speed by at least one third on wet roads and one half on snow; double following distance on slick surfaces.
Question 7 of 20
A sliding fifth wheel that is unlocked or improperly secured can:
Correct. An unsecured sliding fifth wheel can shift during braking, changing the rig's handling unpredictably. Always verify the lock pin is engaged.
Question 8 of 20
Most jackknifes happen because:
Correct. Loss of traction on the tractor drive axles during braking — typically on slick surfaces or with overly aggressive braking — causes a jackknife.
Question 9 of 20
On a tight curve or exit ramp, a tractor-trailer is most likely to roll over because:
Correct. Centripetal forces in a curve push the cargo outward; a high center of gravity multiplies the tipping moment. Slow before the curve.
Question 10 of 20
To make a trailer go where you want when backing, the steering wheel should:
Correct. Backing is opposite-direction steering: to swing the trailer right, turn the wheel left first, then correct as the trailer follows.
Question 11 of 20
When backing a tractor-trailer in a straight line, you should:
Correct. When backing straight, watch the trailer in your mirrors and make small steering corrections to keep it tracking straight. Big corrections lead to jackknifing.
Question 12 of 20
When you supply air to the trailer for the first time after coupling, you should:
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 13 of 20
A sliding fifth wheel allows you to:
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.
Question 14 of 20
If the trailer is too low for coupling, you should:
Correct. Use the landing gear hand crank to raise the trailer to the proper height (just below fifth-wheel level) before backing under.
Question 15 of 20
A sliding-tandem trailer allows you to:
Correct. Sliding tandems shift trailer axles forward (more weight on tractor) or aft (more weight on trailer axles), helping meet axle-weight limits.
Question 16 of 20
Before uncoupling, you should:
Correct. Proper sequence: park level, lower landing gear to support the trailer, disconnect lines, release jaws, then pull forward slowly. Skipping any step risks dropping the trailer.
Question 17 of 20
Combination vehicles are usually:
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 18 of 20
Off-tracking refers to:
Correct. Off-tracking is the tendency for trailer wheels to follow a smaller-radius path than the tractor wheels through a turn, more pronounced with longer wheelbases.
Question 19 of 20
The trailer hand valve should be used:
Correct. Use the trailer hand valve only for testing trailer brakes. Using it to slow the rig can cause the trailer to skid or jackknife.
Question 20 of 20
After connecting the trailer, before pulling away, you should always:
Correct. Always visually confirm: no gap between fifth wheel and trailer plate, jaws closed around the kingpin shank, locking lever fully in place.
About the Alabama 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 Alabama Law Enforcement Agency Driver License Division 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 Alabama CDL practice tests.