Combination vehicles practice test
Every Class A applicant takes the combination vehicles knowledge test on top of general knowledge. It covers what makes a tractor-trailer different: coupling and uncoupling, the trailer air system, and why combinations jackknife and roll.
Combination Vehicles Question 1 of 10
You cross the air lines when hooking up to an OLD trailer without spring brakes. The danger is:
What the test covers
The combination test draws from Section 6 of the CDL manual:
- Rollover and jackknife prevention — low cargo, gentle steering, why empty trailers skid first
- Offtracking and the buttonhook right turn
- The trailer air system: service (blue) and emergency (red) lines, glad hands, the tractor protection valve, and the red eight-sided trailer air supply knob
- Coupling: fifth wheel height, jaws locked around the kingpin shank, the tug test, landing gear fully raised
- Uncoupling in the right order, on ground that supports the trailer
- The antilock brake indicator lamps on tractors and trailers
Coupling is where points are lost
The coupling sequence shows up both on this written test and again on your skills test pre-trip. Learn it as a physical sequence, not a list of facts: chock the trailer, back the fifth wheel under so the trailer lifts slightly, lock the jaws around the kingpin shank, tug test against locked trailer brakes, inspect for no gap between the plates, connect and secure the air lines, then raise the landing gear fully before moving.
Frequently asked
- Who has to take the combination vehicles test?
- Anyone applying for a Class A CDL — the license that covers tractor-trailers and any combination with a towed unit over 10,000 lbs GVWR. Class B and C drivers skip it.
- How many questions does it have?
- Typically about 20 questions, passing around 80%. The trailer air system and coupling steps make up the bulk of the test.
- Is this the same as the doubles/triples test?
- No. Combination vehicles is the baseline Class A test for one trailer. Pulling two or three trailers additionally requires the T (doubles/triples) endorsement and its own knowledge test.