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Drivers who want to drive combination vehicles must pass the combination vehicles test. The District of Columbia CDL combination test consists of 20 questions, and you'll need at least 16 correct answers to pass (80%). The test covers the combination vehicles section of the District of Columbia CDL Manual. Take this practice test now to prepare for the actual DC CDL combination test!
1. The service line is also called:
carrier line or control line.
control line or signal line.
signal line or air line.
pressure line or signal line.
2. Empty trucks require _____ stopping distances because empty vehicles have ______ traction.
less; less
greater; less
greater; more
less; more
3. Which of the following is NOT a warning sign of fatigue?
Heavy eyelids
Frequent blinking
Trouble remembering the last few miles driven
Driving at the speed of the traffic
4. If ABS is not working:
you will not have any brakes.
you should use the parking brake.
you should use the emergency brake.
you will still have brakes.
5. When backing a trailer on a curved path you should back towards:
neither side (back up straight).
the driver's side.
either side.
the passenger's side.
6. Glad hands are used to:
connect the brakes from the truck or tractor to the trailer.
connect the electrical lines from the truck or tractor to the trailer.
connect the service and emergency air lines from the truck or tractor to the trailer.
the air compressor is connected to the engine.
7. A steering wheel should have no more than _____ of play. If there is more play than this, it may be hard to steer.
10 degrees
15 degrees
It doesn't matter.
30 degrees
8. If your vehicle thumps or vibrates heavily, it may be a sign that:
the engine belt is loose.
you need to shift up.
one of the tires has gone flat.
the brakes have failed.
9. When checking air brakes on combination vehicles, which of the following is NOT part of checking that air flows to all trailers?
Going to the rear of the rig.
Opening the emergency line shut-off valve at the rear of the last trailer.
Pulling tractor forward until the fifth-wheel comes out from under the trailer.
Using the trailer handbrake to provide air to the service line.
10. When the tractor protection valve closes, the trailer _______ brakes will come on.
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DC CDL Combination Test

Number of questions: 20
Correct answers to pass:16
Passing score:80%
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