Signals and signalling systems
What this domain tests
The exam tests whether you can read signal aspects as a sequence and plan the train accordingly. You need running signals, distant signals, home, starter and section signals, subsidiary signals such as call-on and shunt, route indicators, banner repeaters, and the systems that back them up: AWS, TPWS, and ETCS.
Reading the sequence
- Green: proceed; observe the permissible speed and route.
- Double yellow: the next signal is at single yellow; begin planning to stop at the following signal.
- Single yellow: the next signal is at red; brake now, not when the red appears.
- Red: stop short of the signal, secure, and contact the signaller.
- Route indicator: shows which route is set. A main aspect does not necessarily mean the diverging route is clear at line speed.
Systems that back up the signal
AWS gives an audible warning and visual indication when approaching certain signals; TPWS can intervene if you pass a signal at danger or exceed a speed trap. ETCS displays a movement authority in the cab. None of these replaces observing the signal and knowing the route.
Worked example
You see double yellow, then single yellow, then red. What does the sequence tell you?
Reasoning: double yellow warns that the next signal is single yellow; single yellow warns that the next is red. You should already be braking to stop at the red, not waiting until you see it. At the red, stop short, secure the train, and contact the signaller. If the red is on a blind curve, your route knowledge should have told you where to begin braking.
Traps that cost marks
- Misreading a route indicator as a main aspect.
- Assuming a green aspect authorises line speed through a junction.
- Ignoring AWS because it “always sounds” on a familiar route.