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

The trailer overheats

Answer

The engine stalls

Answer

The landing gear collapses

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

The fifth wheel is dry and ungreased

Answer

The fifth wheel plate is exactly level with the trailer floor

Answer

The trailer air lines are connected before coupling

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

Apply service brakes at highway speed and note stopping distance

Answer

Apply the parking brake only and release it quickly

Answer

Have a passenger watch the trailer wheels while you drive past

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

Disconnect the air lines first

Answer

Remove the kingpin safety lock

Answer

Drain the air tanks completely

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

Service line (blue)

Answer

Auxiliary supply line (green)

Answer

Control line (yellow)

Question 6

What is rearward amplification in a doubles or triples combination?

Accepted Answer

The tendency of the rear trailer to whip more violently than the front during swerving

Answer

The increase in engine noise at higher speeds

Answer

The amplified braking force at the rear axle

Answer

The magnified turn radius of a long combination