CDL combination vehicles practice test
The combination vehicles test is required for a Class A CDL. It covers how a tractor and trailer behave together, coupling and uncoupling step by step, inspecting the fifth wheel and air lines, and the rollover and jackknife risks that come with a trailer. The sample questions below come from Section 6 of the FMCSA CDL manual.
- 20questions on the real test
- 80%pass mark, 16 correct answers
- 50questions in the PassRig bank
- S6of the FMCSA CDL manual
Free combination vehicles practice quiz
Ten questions from the PassRig bank. Tap an answer to lock it in and read why it is right, with the manual section it comes from. The score keeps count; 80% is the pass mark. The full bank, timed mock exams and mistake review live in the app.
0 of 10 right0 of 10 answered
Compared with an empty rig, a fully loaded tractor-trailer is about how much more likely to roll over in a crash?
Answer: D. Ten times as likelyA loaded combination has a high center of gravity and rolls over far more easily. Keep the load low and centered, and slow down well before curves and ramps.
Source: FMCSA CDL Manual, Section 6.1.1 (Rollover Risks)
When backing a trailer, to make the trailer go left you should:
Answer: B. Turn the top of the steering wheel to the rightThe trailer goes the opposite way from the top of the steering wheel. Turn right to push the trailer left, then straighten and follow it. Back toward the driver's side when you can, use pull-ups to fix your angle, and get out and look.
Source: FMCSA CDL Manual, Section 6.1.7 (Backing With a Trailer)
After coupling, how should the fifth wheel look when you inspect it with a flashlight?
Answer: B. No space between the upper and lower fifth wheel, and the locking jaws closed around the shank of the kingpinAny gap means the trailer is riding high and not locked. The jaws must grip the shank, the narrow part of the kingpin, not the head. Also check that the locking lever is in the lock position and the safety latch is over it.
Source: FMCSA CDL Manual, Section 6.4.1 (Coupling Tractor-Semitrailers: Inspect the Coupling)
When you turn suddenly while pulling doubles, which trailer is most likely to turn over?
Answer: A. The rear trailerRearward amplification, the crack-the-whip effect, grows toward the back of the rig. A rearward amplification of 2.0 means the rear trailer is twice as likely to turn over as the tractor, and the last trailer of triples can roll 3.5 times as easily as a 5-axle tractor-semitrailer. Steer gently and avoid quick lane changes.
Source: FMCSA CDL Manual, Section 6.1.2 (Steer Gently)
The trailer starts to skid and swing out in a jackknife. The best way to stop it is to:
Answer: C. Release the brakes so the trailer wheels can regain tractionTrailer jackknifes come from trailer wheels locking up. Once they roll again they will grip the road, and the trailer will straighten out behind the tractor. Do not use the trailer hand valve.
Source: FMCSA CDL Manual, Section 6.1.5 (Prevent Trailer Skids)
The service air line carries air to the trailer brakes whenever you:
Answer: A. Press the brake pedal or use the trailer hand valveThe service line is controlled by the foot brake and the hand valve. How hard you press sets how much pressure goes down the line and how hard the trailer brakes apply.
Source: FMCSA CDL Manual, Section 6.2.4 (Service Air Line)
The air tanks on a trailer are filled through the:
Answer: D. Emergency (supply) lineThe red emergency line charges the trailer air tanks and holds the trailer emergency brakes released. Like the tractor's tanks, trailer tanks collect water and oil and must be drained.
Source: FMCSA CDL Manual, Section 6.2.6 (Trailer Air Tanks)
Before coupling, the fifth wheel should be tilted:
Answer: C. Down toward the rear of the tractorWith the fifth wheel tilted down toward the rear of the tractor, the kingpin can enter the fifth wheel as you back under. Also check that the jaws are open, the safety unlocking handle is in the automatic lock position, a sliding fifth wheel is locked, and the trailer kingpin is not bent or broken.
Source: FMCSA CDL Manual, Section 6.4.1 (Coupling: Inspect Fifth Wheel)
After raising the landing gear all the way up, you should:
Answer: A. Secure the crank handle and check for enough clearance between the tractor and the landing gear and trailerRaise the landing gear all the way up and secure the crank handle. Never drive with the landing gear only part way up; it can catch on railroad tracks. With the trailer's full weight on the tractor, check that the rear of the tractor frame will clear the landing gear in a sharp turn and that the top of the tractor tires clears the nose of the trailer.
Source: FMCSA CDL Manual, Section 6.4.1 (Coupling: Raise Front Trailer Supports)
During the inspection of a combination vehicle, the lower fifth wheel should be:
Answer: D. Securely mounted to the frame with no missing or damaged parts, and no visible gap between it and the trailerLook for missing bolts, cracks, and a gap between the upper and lower fifth wheel plates. The locking jaws must be around the kingpin shank, the release lever locked, and the safety latch in place.
Source: FMCSA CDL Manual, Section 6.5.1 (Coupling System Areas)
What the combination vehicles test covers
- Driving combination vehicles: rollover, offtracking and jackknife
- Trailer hand valve and trailer brakes
- Combination vehicle air brakes: service, emergency and supply lines
- Coupling and uncoupling, in order
- Inspecting a combination vehicle
- Antilock brakes on tractors and trailers
Who needs it
Every Class A applicant. If you will pull a trailer, this test is required.
The test has 20 multiple-choice questions and the passing score is 80%, so you can miss 4. Your state DMV or DOT administers it; the federal rules are on the FMCSA CDL page. Study Section 6 of the CDL manual alongside these questions.
More CDL practice tests
Combination Vehicles test questions
How many questions are on the CDL combination vehicles test?
20 questions. 16 correct answers reach the 80% pass mark.
Do I need the combination test for a Class B licence?
No. Class B covers single vehicles. The combination vehicles test is a Class A requirement, because Class A means you tow a trailer over 10,000 pounds.
What is the hardest part of the combination vehicles test?
The coupling and uncoupling sequence and the air line questions. Learn the order of the steps and what each air line does before test day.