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District Of Columbia CDL Permit Test - Combination

Number of questions: 20
Passing score: 16
Directions: All applicants who are applying for a Class A CDL should be prepared to take the Combination test. This test covers information found in Section 6 of the Commercial Driver License Manual. Section 6 provides the information needed to safely operate tractor-trailers, doubles, triples, and straight trucks with trailers. The test is made up of 20 multiple-choice questions, and applicants will have one hour to correctly answer a minimum of 16 questions. The Combination test is not a replacement for the Double/Triple endorsement test.
You have made error so far
Passing grade —
4 or fewer errors
Which of the following types of vehicles is most prone to the “crack-the-whip" effect?
An automobile
A three-axle tractor
A bobtail tractor
A triple combination
If unsure if a trailer is equipped with ABS, you can:
Check under the trailer for wheel speed sensors coming from the back of the brakes.
Try driving on a slippery surface and see if ABS kicks in.
Assume it does have ABS.
Remove a tire and look for the ABS sensor on the axle.
Using the trailer hand brake while experiencing a trailer jackknife will:
Stop the skid.
Straighten the trailer.
Increase traction.
Continue the skid.
When the wheels of a trailer lock up:
The trailer will stay straight.
The trailer tends to swing around.
The cab will swing, but the trailer will stay straight.
They will likely go flat.
To prevent a trailer from rolling over, you should:
Speed up when nearing a corner.
Make sudden steering moves.
Take on-ramps faster than the posted speed limit.
Drive slowly around corners.
In a sudden turn, the ____ trailer is the most likely to turn over.
A shut-off valve:
Is located on the front of a trailer.
Is located on the instrument panel.
Prevents air from escaping an air brake system.
Should always be open.
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