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CDL Practice Test: Combination Vehicles

These CDL practice questions are from our High Road Training Program, a CDL test preparation course designed to help you learn the CDL manual.

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CDL Practice Test: Combination Vehicles

Combination Vehicles Questions

Click On The Picture To Begin

Good Luck!

How far should the trailer landing gear be raised?
  • On light loads, only half way but on heavy loads, it should be raised all the way up
  • Half way up
  • 3/4 of the way up
  • All the way up
This is a question from page 52 - click here to look up the answer

Quote From Page 77 Of The Illinois CDL Manual:

Raise The Front Trailer Supports (Landing Gear)

  • Use low gear range (if so equipped) to begin raising landing gear. Once free of weight, switch to the high gear range.
  • Raise landing gear all the way up. (Never drive with landing gear only part way up, as it may catch on railroad tracks or other things.)
  • After raising landing gear, secure crank handle safely.
  • When full weight of trailer is resting on tractor:
  • Check for enough clearance between rear of tractor frame and landing gear. (When the tractor turns sharply, it must not hit landing gear.)
  • Check that there is enough clearance between the top of the tractor tires and the nose of the trailer
Next
What is the usual color for the Emergency Line?
  • Green
  • Black
  • Red
  • Blue
This is a question from page 49 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

Emergency lines are often coded with the color red (red hose, red couplers or other parts) to keep from getting them mixed up with the blue service line.

TruckingTruth's Advice:

While the emergency line will almost always be red, the color is not a regulation so some trucks may use other colors.

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Next
What is the usual color for the Service Line?
  • Orange
  • Blue
  • Red
  • Green
This is a question from page 49 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

Emergency lines are often coded with the color red (red hose, red couplers or other parts) to keep from getting them mixed up with the blue service line.

TruckingTruth's Advice:

While not an actual regulation, the normal color scheme is usually as follows:

  • Emergency Line: Red
  • Service Line: Blue
  • Electrical Line: Green

Again, these are not actual regulations so colors may vary from truck to truck, but these colors have become the industry norm.

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Next
What is a correct way to test the trailer emergency brakes?
  • While idling in the lowest gear possible, pull out the yellow parking brake control to see if you come to a safe stop
  • While stopped, pull out the yellow parking brake control and pull gently on the trailer with the tractor
  • While idling in the lowest gear possible, pull out the trailer air supply control to see if you come to a safe stop
  • While stopped, pull out the trailer air supply control and pull gently on the trailer with the tractor
This is a question from page 54 - click here to look up the answer

Quote From Page 79 Of The Illinois CDL Manual:

Test trailer emergency brakes: Charge the trailer air brake system and check that the trailer rolls freely. Then stop and pull out the trailer air supply control (also called "tractor protection valve control" or "trailer emergency valve") or place it in the "emergency" position. Pull gently on the trailer with the tractor to check that the trailer emergency brakes are on.

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Next
When you turn suddenly while pulling doubles, which trailer is most likely to turn over?
  • The tractor is more likely to turn over than either trailer
  • The front trailer
  • Both trailers are equally as likely to turn over
  • The rear trailer
This is a question from page 48 - click here to look up the answer

Quote From Page 70 Of The Illinois CDL Manual:

Trucks with trailers have a dangerous "crack-the-whip" effect. When you make a quick lane change, the crack-the-whip effect can turn the trailer over. There are many accidents where only the trailer has overturned.

"Rearward amplification" causes the crack-the-whip effect. The rear trailer is twice as likely to turn over as the tractor. You can roll the last trailer of triples 3.5 times as easily as a 5-axle tractor-semi.

TruckingTruth's Advice:

When pulling more than 1 trailer, the rear-most trailer is always at a higher risk of overturning than the front trailer.

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Next
How should you position your tractor before backing under and connecting to a trailer?
  • Back the tractor directly in front of the trailer
  • Back the tractor to the trailer on the left side
  • Back the tractor to the trailer at a 45 degree angle on either the left or right side
  • Back the tractor to the trailer on the right side
This is a question from page 51 - click here to look up the answer

Quote From Page 75 Of The Illinois CDL Manual:

  • Put the tractor directly in front of the trailer. (Never back under the trailer at an angle because you might push the trailer sideways and break the landing gear.)
  • Check position, using outside mirrors, by looking down both sides of the trailer.

TruckingTruth's Advice:

It will take some practice, but always back under a trailer as straight as possible to avoid turning the trailer over.

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Next
What are Glad Hands?
  • Caps which cover the valve stems on tires
  • Used to secure the trailer kingpin to the tractor 5th wheel
  • A name for the yellow and red air valves in the cab of a truck
  • Coupling devices used to connect the service and emergency air lines from the truck or tractor to the trailer
This is a question from page 50 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

"Glad hands" are coupling devices used to connect the service and emergency air lines from the truck or tractor to the trailer.

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Next
What does the term "Bobtail" refer to?
  • A tractor without a trailer attached
  • A parked trailer with no truck attached
  • A truck and trailer that is not loaded
  • A fully loaded truck and trailer
This is a question from page 48 - click here to look up the answer

Quote From Page 71 Of The Illinois CDL Manual:

You also must be very careful about driving "bobtail" tractors (tractors without semitrailers). Tests show that bobtails can be very hard to stop smoothly. It takes them longer to stop than a tractor-semitrailer loaded to maximum gross weight.

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