Passenger Safety and Air Brakes Flashcards

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

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

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.

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

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

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.

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

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

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.

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

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

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.

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

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

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.

What is the purpose of EBS (Electronic Braking System) on modern commercial vehicles?

Answer: EBS integrates ABS, traction control, stability control, and optimised brake force distribution electronically — improving safety and brake efficiency

EBS (Electronic Braking System) uses electronic control to optimise brake force distribution across axles, integrating ABS, traction control, and stability systems. It improves braking performance and reduces stopping distances.