DTT HGV Coupling and Uncoupling Trailers 3

Question 1

The yellow (service) airline on a truck-trailer combination is used for:

Accepted Answer

Controlling the service (foot) brakes on the trailer

Answer

The yellow service line transmits braking signals from the driver's foot brake to the trailer's service braking system during normal driving.

Question 2

If you discover a cracked or damaged kingpin during a pre-coupling inspection, you should:

Accepted Answer

Not couple the trailer until the kingpin has been repaired or replaced

Answer

A damaged kingpin could fail under load and cause the trailer to detach from the tractor, creating an extreme danger to all road users.

Question 3

What is the risk if the fifth wheel height is too high when coupling?

Accepted Answer

The kingpin may not lock fully into the fifth wheel jaws

Answer

If the fifth wheel is too high, the kingpin will ride up on the edge of the fifth wheel plate rather than dropping into the jaw, resulting in an insecure or failed coupling.

Question 4

After uncoupling a trailer, before driving the tractor unit away, you should check:

Accepted Answer

That the trailer is stable and the fifth wheel jaws are clear of all obstructions

Answer

Confirming the trailer is stable and the fifth wheel is fully clear prevents damage to the coupling and ensures the tractor can drive away safely.

Question 5

What does 'bobtail' mean in the context of truck driving?

Accepted Answer

Driving a tractor unit without a trailer attached

Answer

A 'bobtail' tractor is a tractor unit being driven without a trailer; this condition affects braking distance and handling due to the different weight distribution.

Irish DTT Truck/Bus Practice Test

Irish DTT Truck/Bus Practice Test

DTT HGV Coupling and Uncoupling Trailers 3