Signaling and Train Control
Signaling and train control tests the safety logic that keeps trains apart and supervises speed. The exam covers interlocking principles, track vacancy detection, ATP/ATC, and automatic operation levels.
Core rules
- Interlocking is fail-safe: routes lock, points prove, flank protection and overlap are enforced, and conflicting routes cannot be set.
- Track circuits detect a train by shunting the rails; audio-frequency and coded types resist traction interference. Axle counters count wheels in and out and do not depend on rail contact.
- ATP supervises speed and braking to a movement authority. ETCS Level 2 uses radio but still needs track vacancy detection; Level 3 moves the train-position function onboard. CBTC gives moving-block operation.
- GoA 0–4 grades automation; GoA 2 is semi-automatic with a driver, GoA 4 is unattended.
Worked example
A train approaches a stop at 100 km/h (27.8 m/s). Service brake rate is 0.7 m/s² and reaction time is 3 s. Reaction distance = 27.8 × 3 = 83 m. Braking distance = v²/(2a) = 27.8²/1.4 ≈ 552 m. The movement authority must extend at least 635 m beyond the stop, plus safety margin. Using 100 km/h as 100 m/s would be a factor-of-3.6 error.
Traps
- Saying ETCS Level 2 needs no track circuits at all.
- Equating a GoA level with an ATP level.
- Using the wrong unit conversion for km/h.
- Forgetting overlap and reaction distance.