DTT HGV Coupling and Uncoupling Trailers 2 — Questions and Answers
Question 1: What is a 'fifth wheel' coupling on a heavy goods vehicle?
- A spare wheel mounted at the rear of the tractor unit
- The coupling device on the tractor that locks onto the trailer kingpin (Correct answer)
- The fifth wheel of the steering axle assembly
- An additional support axle fitted under the trailer
Correct answer: The coupling device on the tractor that locks onto the trailer kingpin
The fifth wheel is the horse-shoe-shaped coupling plate mounted on the rear of the tractor unit that receives and locks around the trailer's kingpin.
Question 2: Before uncoupling a trailer on a public road, you must ensure:
- The trailer is on level, firm ground with the brakes applied (Correct answer)
- Only the electrical cable has been disconnected
- All cargo has been removed from the trailer
- The RSA has been notified of the uncoupling
Correct answer: The trailer is on level, firm ground with the brakes applied
Level, firm ground ensures the trailer will not roll or tip when uncoupled, and applied brakes prevent any unintended movement.
Question 3: What is the purpose of the landing gear (dolly legs) on a semi-trailer?
- To provide additional braking force when loaded
- To support the front of the trailer when uncoupled from the tractor (Correct answer)
- To lower the trailer bed for easier loading
- To stabilise the trailer during sharp cornering
Correct answer: To support the front of the trailer when uncoupled from the tractor
The landing gear is cranked down before uncoupling to support the nose of the trailer and keep it level when not connected to the tractor unit.
Question 4: Which of the following would indicate a faulty fifth wheel coupling?
- The trailer sways slightly at motorway speeds
- The locking jaws do not fully close around the kingpin (Correct answer)
- The trailer lights flicker when braking
- The air pressure takes longer than usual to build up
Correct answer: The locking jaws do not fully close around the kingpin
If the fifth wheel locking jaws do not fully close around the kingpin, the trailer is not properly secured and could detach from the tractor.
Question 5: When coupling a trailer in poor visibility conditions such as at night, what is recommended?
- Proceed quickly to minimise time exposed in the dark
- Use a banksman or spotter to guide the reversing driver (Correct answer)
- Avoid coupling trailers entirely in poor visibility
- Rely solely on the vehicle's reversing camera
Correct answer: Use a banksman or spotter to guide the reversing driver
A banksman provides real-time guidance and can communicate obstacles or misalignments that cameras or mirrors may not clearly show in poor visibility.
Question 6: Before driving away after coupling a trailer, what must you confirm about the trailer brakes?
- That the brakes make a hissing sound when applied
- That the trailer brakes function correctly and are released for travel (Correct answer)
- That the trailer brakes remain permanently applied during driving
- That the brake warning light on the dash is extinguished
Correct answer: That the trailer brakes function correctly and are released for travel
The trailer brakes must be tested to confirm they work, then released so the vehicle can move; driving with trailer brakes applied causes overheating and damage.
Question 7: At what point should you stop reversing the tractor unit when coupling to a trailer?
- When the trailer is approximately 1 metre behind the tractor cab
- When you hear or feel the fifth wheel jaws lock onto the kingpin (Correct answer)
- When the tractor unit's rear bumper makes contact with the trailer
- When the trailer's reversing lights illuminate
Correct answer: When you hear or feel the fifth wheel jaws lock onto the kingpin
The audible click and physical resistance indicate that the fifth wheel jaws have engaged and locked around the kingpin, confirming a successful coupling.
DTT HGV Coupling and Uncoupling Trailers 2
What is a 'fifth wheel' coupling on a heavy goods vehicle?