PTS Railway Hazards and Terminology 5 — Questions and Answers
Question 1: What is a 'SPAD' (Signal Passed At Danger) in railway safety?
- A track defect report filed after a routine inspection
- An incident where a train passes a signal displaying a stop aspect without authority (Correct answer)
- A scheduled possession activity document issued by the controller
- A speed restriction imposed after adverse weather conditions
Correct answer: An incident where a train passes a signal displaying a stop aspect without authority
A SPAD occurs when a train passes a signal showing a red (danger) aspect without authorization, which is a serious safety incident that can lead to collisions.
Question 2: Which of the following best describes the hazard of 'trespass' on railway property?
- Legal liability for the trespasser only, with no direct safety risk to others
- Exposure to moving trains, electrified equipment, and other hazards without protection or warning (Correct answer)
- A minor risk managed entirely by perimeter fencing along the line
- A hazard that only exists during hours of darkness
Correct answer: Exposure to moving trains, electrified equipment, and other hazards without protection or warning
Trespassers face severe risks from trains that cannot stop quickly, electrified rails or OLE, and other hazards, often without any warning system in place for them.
Question 3: What does 'track circuit block' (TCB) signaling rely on to detect trains?
- GPS transponders fitted to every locomotive and wagon
- The electrical conductivity of steel wheels bridging a low-voltage circuit between the two rails (Correct answer)
- Infrared sensors mounted at regular intervals at the trackside
- Weight sensors embedded in the sleepers under each rail
Correct answer: The electrical conductivity of steel wheels bridging a low-voltage circuit between the two rails
Track circuit block signaling detects trains by using the train's steel wheels and axles to complete a low-voltage electrical circuit between the two rails, triggering the signaling system.
Question 4: What is the primary hazard when working inside a non-electrified railway tunnel?
- Falling debris from the tunnel roof combined with very limited escape routes if a train approaches (Correct answer)
- Excessive heat buildup caused by trains passing through in both directions
- Tunnel acoustics magnifying distant train noise, making warnings inaudible
- Risk of flooding from underground water tables beneath the invert
Correct answer: Falling debris from the tunnel roof combined with very limited escape routes if a train approaches
Tunnels present heightened risk because escape options are severely limited, noise echoes make train approach difficult to judge, and falling debris from aging structures is a constant danger.
Question 5: What is 'rail creep' and what structural problem can it cause?
- Gradual longitudinal movement of rails due to traction and braking forces, which can open or close rail joints dangerously (Correct answer)
- Slow lateral spreading of rails on curves due to centrifugal forces
- Progressive sinking of the track into soft subgrade over time
- Corrosion of fasteners that allows the rail to rotate in its rail seat
Correct answer: Gradual longitudinal movement of rails due to traction and braking forces, which can open or close rail joints dangerously
Rail creep causes rails to shift along their length, potentially opening joints on one side and closing them on the other, creating a structural instability hazard.
Question 6: What does 'degraded mode working' mean in a railway signalling context?
- Operating trains at reduced power to conserve energy during off-peak hours
- Operating the railway under alternative rules when normal signalling equipment has failed (Correct answer)
- Reducing train frequency during periods of severe staff shortages
- Using older mechanical signals instead of electronic ones during planned maintenance windows
Correct answer: Operating the railway under alternative rules when normal signalling equipment has failed
Degraded mode working applies when signalling systems fail, requiring trains to operate under alternative authorities such as piloting, token working, or written verbal authority.
Question 7: What is 'differential settlement' of track and why does it create a derailment risk?
- Uneven sinking of the track formation at different rates, creating twist or vertical misalignment in the track geometry (Correct answer)
- The difference in wear rate between inner and outer rails on a curve
- Variation in sleeper spacing that develops progressively over years of heavy traffic
- Settlement of ballast on one side causing gauge widening on a straight section
Correct answer: Uneven sinking of the track formation at different rates, creating twist or vertical misalignment in the track geometry
Differential settlement causes one section of track to sink more than an adjacent section, creating twist geometry that can lift a wheel off the rail and cause derailment.
PTS Railway Hazards and Terminology 5
What is a 'SPAD' (Signal Passed At Danger) in railway safety?