DTT HGV Passenger Safety and Air Brakes 4

Question 1

What is 'jackknifing' and how can a truck driver prevent it?

Accepted Answer

The trailer pivots around the fifth wheel creating a V-shape — prevented by gradual braking, avoiding over-braking the tractor while trailer brakes lock

Answer

Jackknifing occurs when the trailer's braking locks the trailer wheels causing it to swing outward while the tractor continues forward. Prevent by using progressive braking, avoiding over-braking on slippery surfaces.

Question 2

What is 'trailer swing' and how does it differ from jackknifing?

Accepted Answer

Trailer swing (snaking) is lateral oscillation of the trailer — usually caused by excessive speed for the condition, while jackknifing is a braking-induced fold at the coupling

Answer

Trailer swing (snaking) is a side-to-side oscillation of the trailer that worsens with speed. It is typically caused by excessive speed for load/wind conditions. Jackknifing is a distinct braking-related fold at the coupling point.

Question 3

What is the correct response if trailer swing begins on a motorway?

Accepted Answer

Ease off the accelerator gently and do not brake — gradual deceleration without braking often allows the trailer to stabilise

Answer

If trailer swing begins, ease off the accelerator smoothly — do not brake, as braking worsens the oscillation. If the swing is severe, progressive gentle braking after the speed has reduced may be needed.

Question 4

What should a bus driver do in an emergency evacuation of the vehicle?

Accepted Answer

Stop safely, apply spring brakes and engine stop, open all emergency exits, direct passengers calmly to exit, assist mobility-impaired passengers, and call emergency services

Answer

In an emergency evacuation: secure the vehicle (handbrake, engine off), activate hazards, open all emergency exits, calmly direct passengers to safe exits, assist those unable to self-evacuate, and call 999.

Question 5

What is the function of load sensing valves in an air brake system?

Accepted Answer

They adjust the braking force to the axle based on the load carried — preventing wheel lock on lightly loaded axles

Answer

Load sensing valves modulate the brake air pressure delivered to rear axles based on the suspension compression (which indicates load). This prevents wheel lock on empty or lightly loaded axles.

Irish DTT Truck/Bus Practice Test

Irish DTT Truck/Bus Practice Test

DTT HGV Passenger Safety and Air Brakes 4