Free CDL Combination Vehicles Practice Test 2026
The Combination Vehicles test is required for a Class A CDL. It covers coupling and uncoupling tractor-trailers, inspecting combination vehicles, and the special handling characteristics of pulling a trailer.
What is 'off-tracking' (sometimes called 'cheating')?
About the CDL Combination Vehicles Test
Pulling a trailer turns one vehicle into two that don't always travel the same path. Required for a Class A CDL, the Combination Vehicles test focuses on coupling and uncoupling a tractor-trailer in the correct order, inspecting the fifth wheel, kingpin, and the air and electrical lines, and handling off-tracking - where the trailer's wheels cut inside the tractor's path through a turn. It also covers preventing the trailer skids and rollovers that combination units are especially prone to.
What's on the CDL Combination Vehicles knowledge test
The Combination Vehicles knowledge test is written from Section 6 (Combination Vehicles) of the national CDL manual, the text every state's CDL manual follows. You take it only if you need the CV endorsement or drive a vehicle that requires it.
Federal rules fix the pass mark at 80 percent for every CDL knowledge test, but leave the number of questions to each state, so check your own state's CDL manual for the exact count. This practice test uses all 16 questions in our Combination Vehicles bank, each checked against the manual page shown with it.
- Number of questions
- Set by each state: federal rules require a set number of questions, with a prescribed number from each knowledge area (49 CFR 383.133)
Manual sections this test is drawn from
- Section 6: Combination Vehicles - Driving Combination Vehicles, Combination Vehicle Air Brakes, Antilock Brake Systems, Coupling and Uncoupling, Inspecting a Combination Vehicle
Sample questions from this test, with answers
Want to test yourself first? Take the test above before reading these. Every answer below is checked against the source shown.
1. What usually causes a 'trailer jackknife'?
- A. The trailer wheels locking up when braking (correct)
- B. Steering the tractor too slowly in turns
- C. Backing the trailer in a straight line
- D. Driving with the fifth wheel too far back
Why: When the trailer wheels lock, the trailer tends to swing around, especially when it is empty or lightly loaded. Check your mirrors when braking hard, and release the brakes to get traction back.
Source: National CDL Manual, p.6-2 (PDF p.86), 6.1.5 Prevent Trailer Skids
2. Before uncoupling a semitrailer, where should you park it?
- A. On a slight downhill so it is easy to leave
- B. On soft ground so the landing gear sets in
- C. On a surface firm enough to hold its weight (correct)
- D. Anywhere, since the surface does not matter
Why: Make sure the parking surface can support the trailer's weight, and line the tractor up with the trailer because pulling out at an angle can damage the landing gear. Chock the trailer wheels if it lacks spring brakes.
Source: National CDL Manual, p.6-9 (PDF p.93), 6.4.2 Step 1 Position Rig
3. Why should you never use the trailer hand valve (trolley valve) to park?
- A. It applies only the brakes on the tractor
- B. It locks the fifth wheel jaws open
- C. It drains the tractor's air tanks
- D. Air can leak out and release the brakes (correct)
Why: The hand valve works the trailer brakes with air, which can leak away and unlock them on trailers without spring brakes. Always use the parking brakes, and chock trailers that do not have spring brakes.
Source: National CDL Manual, p.6-4 (PDF p.88), 6.2.1 Trailer Hand Valve
4. What connects the service and emergency air lines from the tractor to the trailer?
- A. The kingpin
- B. The fifth wheel
- C. Glad hands (correct)
- D. The landing gear
Why: Glad hands are the couplers for the air lines. Clean the couplers and their rubber seals before connecting, then press the seals together at a 90 degree angle and turn to lock.
Source: National CDL Manual, p.6-5 (PDF p.89), 6.2.5 Hose Couplers (Glad Hands)
5. What is the landing gear on a semitrailer?
- A. Rear wheels that carry the trailer load
- B. The plate that locks onto the kingpin
- C. Front supports that hold up the trailer (correct)
- D. The lights that mark the trailer's sides
Why: The landing gear is the set of front trailer supports. Lower it before uncoupling, and raise it all the way before driving so it cannot catch on railroad tracks or other objects.
Source: National CDL Manual, p.6-9 (PDF p.93), 6.4.1 Step 15 Raise Front Trailer Supports
6. Why does an empty or lightly loaded combination need extra care when braking?
- A. It rolls over more easily than a full one
- B. It always stops in a shorter distance
- C. Its brakes receive less air pressure
- D. Its wheels lock up more easily (correct)
Why: A lightly loaded rig has stiff springs and strong brakes but poor traction, so its wheels lock easily and it can take longer to stop than a full one. The trailer can swing out or the tractor can jackknife.
Source: National CDL Manual, p.6-1 (PDF p.85), 6.1.3 Brake Early
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