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Air pressure drops to a level between 20 and 45 psi.
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You are experiencing a trailer jackknife.
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Wheels have regained traction after a skid.
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Air pressure is above 45 psi.
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Pennsylvania CDL Permit Test - Combination
(From the 2021 Pennsylvania CDL driver handbook)
| 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's 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 need to correctly answer a minimum of 16 questions to pass. The Combination test is not a replacement for the Double/Triple endorsement test.
Passing grade —
4 or fewer errors
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1.
In a vehicle equipped with an automatic tractor protection valve, the valve will pop out when:
2.
Failure to keep the fifth wheel plate properly greased could:
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Cause the trailer to disconnect.
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Cause steering problems.
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Cause braking problems.
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Affect the lights.
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3.
When coupling a trailer:
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Make sure to couple matching glad hands.
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Any glad hand can be connected to any other glad hand.
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It is best to leave one glad hand unattached.
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Only one set of glad hands should be connected.
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4.
A loss of air pressure in the emergency line will cause:
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The suspension springs to extend.
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The tractor protection valve to open.
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The rear trailer to detach from the combination.
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The emergency brakes to activate.
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5.
Fully-loaded rigs:
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Are less likely to roll over than empty rigs.
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Are more likely to roll over than empty rigs.
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Are just as likely to roll over as empty rigs.
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Should not be driven.
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6.
Trailers with low underneath clearance may be difficult to drive:
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On interstate highways.
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Over railroad crossings.
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On dirt roads.
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At the posted speed limit.
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7.
An Anti-Lock Braking System (ABS):
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Allows wheels to lock up.
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Prevents wheels from locking up.
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Makes it easier to turn a large vehicle.
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Assists with the operation of brake lights.
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