Commercial Driving Combination Vehicles

Question 1

What is the primary danger of trailer swing (trailer jackknife)?

Accepted Answer

The trailer swings out and may strike other vehicles or cause a rollover

Answer

During a trailer jackknife, the trailer swings outward uncontrollably and can strike adjacent vehicles, barriers, or cause the entire rig to roll over.

Question 2

When coupling a tractor to a semi-trailer, what must you verify about the fifth wheel?

Accepted Answer

The kingpin is locked in the fifth wheel jaws and the locking lever is secured

Answer

After coupling, you must confirm the kingpin is fully locked in the fifth wheel jaws and the locking handle is in the locked position to prevent separation.

Question 3

What is the correct procedure for testing trailer brakes after coupling?

Accepted Answer

With tractor and trailer connected, move forward slowly while applying only the trailer hand valve

Answer

Moving slowly forward while applying the trailer hand valve confirms trailer brakes are working; drag from the trailer brakes will indicate they are functional.

Question 4

When uncoupling a semi-trailer, what must you do before cranking the landing gear down?

Accepted Answer

Lower the trailer on a firm, level surface and apply the trailer parking brake

Answer

Before cranking down the landing gear, the driver must ensure the trailer is on firm, level ground and the trailer parking brake is set so the trailer cannot roll.

Question 5

Which air line on a combination vehicle supplies continuous air to the trailer to charge the emergency brakes?

Accepted Answer

Emergency line (red)

Answer

The emergency (red) line, also called the supply line, provides continuous pressurized air to charge the trailer's emergency brakes and keep them released.

Commercial Driving Practice Test

Commercial Driving Practice Test

Commercial Driving Combination Vehicles