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CDL Combination Vehicles Cheat Sheet

The 56 highest-yield CDL Combination Vehicles questions with the correct answer and one line of logic each - plus the walk-in document checklist and the signs you must know on sight. Print it, mark it up, walk in calm.

  • 56 exam-style questions with answers and explanations
  • Walk-in checklist: documents, fees, vision test - printable with checkboxes
  • 12 must-know road signs with plain-English meanings
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CDL Combination Vehicles
56 questions inside

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1. A combination vehicle's trailer air brakes use ________ air lines between tractor and trailer.
✓ Two: the service line and the emergency (supply) line
Two air lines connect the tractor to the trailer: the service line (also called the control or signal line), which applies the trailer brakes, and the emergency or supply line, which charges the trailer tanks and controls the trailer's emergency brakes. Both connect through glad hands. Knowing each line's job is essential.
2. Before backing under a trailer, the trailer should be at a height that is ________.
✓ Slightly lower than the fifth wheel, so the trailer is lifted as the tractor backs under
Set the trailer slightly lower than the center of the fifth wheel so that, as you back under, the fifth wheel lifts the trailer a little and the kingpin slides in properly. Too high and the tractor may hit and damage the trailer; too low and it won't couple. Correct trailer height is essential for a secure coupling.
3. Combination vehicles are generally harder to drive than single vehicles because they ________.
✓ Are longer and heavier, with more wheels that can skid
A tractor-trailer is longer, heavier, and has more wheels that can lose traction, so it needs more room to turn, stop, and maneuver. It also reacts to steering differently because of the trailer. These differences make combination vehicles require extra skill and caution.
4. When inspecting a coupled fifth wheel, there should be no ________.
✓ Gap between the fifth wheel plate and the trailer apron
A gap between the fifth wheel and the trailer's apron means the trailer may be resting on top of the fifth wheel without the kingpin locked in, which is extremely dangerous. There should be solid contact with no gap. If you see a gap, do not drive - recouple correctly.
5. A drive-wheel (tractor) skid in a combination vehicle can cause:
✓ The tractor to jackknife (the drive wheels lose traction and the rear swings out)
If the tractor's drive wheels lose traction - from over-braking, too much acceleration, or going too fast - the rear of the tractor can swing out and jackknife. To recover, stop braking to let the wheels roll and steer to keep the rig straight. Smooth inputs prevent drive-wheel skids.
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51 more questions in the PDF