bramling
Veteran Member
Semi-correct (by my understanding at least). It is possible to get a blue signal before the train is ready to depart, but the train should have a target point *and* be communicating with the system - because blue also means that communicating trains (only) can proceed - if there is no target point this could be an issue. Trains can be held by Service Controllers with a blue aspect, meaning no white lights on the bodyside.
A train won’t get the white lights before the blue has illuminated, however.
There seems to be some confusion about this, however from memory I'm fairly sure that the signals at JNUP boundary points would only change from red to blue once the train had received its target point.
There is a bit of an issue with the RTDIs in that they seem to be programmed to give a white visual once the first track in advance of the train has a limit of movement authority over it, even though in some cases more than this is required before the driver sees a "target point" on his in-cab display. This is a problem at somewhere like Embankment northbound as the system will hold a train until the train has a clear run to Charing Cross in order to avoid the rear of the train coming to a stand still in Embankment platform (a LU requirement, not a Thales design principle), What this means in practice is platform staff can see a white visual on the RTDI whilst the driver still has no target point to depart. Whether this behaviour applies to the migration starting signals I couldn't say, though if any S stock drivers on here can comment on this then I'd be interested to hear their experiences.
I've no idea if this has undesirable behaviour has been modified on 4LM.