mark bedford Wrote:I tried the 2007 layout yesterday under exam conditions. Looking through my attempt afterwards has left me confused with terminal platforms (station F) at the end of the single line. I had decide to signal using OTW without staff for this line, in hind sight this may have been pointless as track circuits were require for the AHBC I provided at Grade and a non-blocking signal on the return to protect the crossing.
Back to the terminal, if we have a buffer stop with red lamps then we need a distant which cannot display better than caution. My first thought was a distant board but is there a 20mph/32kmh speed limit to using these, GK/RT0032. However if this wasn't at the end of a single line, then for a terminal station or bay line I would expect MAR/delayed yellow, the buffer stop having no overlap would require the train nearly at a stand before any release of aspect.
GK/RT0051 doesn't mention any speed limits for OTW. As it is a budget system would we expect a speed limit, 20mph or less, near the terminus and a fixed distant board up to the buffer stop?
I'm not even going to consider how TPWS failure or TC interrupter on the buffer stop return to the protecting signal or box indication. The budget is blown!
Mark
I agree that at first sight OTW-NS seems appropriate but also agree that since line is so short and there is level crosssing then continuous train detection is probably the answer. However do remember level crossing predictors exist.
Presumably you felt necessary to have AHBC due to defined speed of line- I agree that since it is approximately in the middle then to make ABCL with a low crossing speed would mean train would never get to a decent speed anywhere on branch (different case had it been close to terminal stn though).
I'd have gone for distant board; they always used to be used on lines with higher speed than that. Indeed I saw oneon the Cambrian line protecting a level crossing near Criccieth when on holiday last week and I am sure permissible speed is higher than that, though to be fair all passeger trains would have stopped at station immediately prior to it in normal course of events).
The RSSB server is down and can't lay my hands on copy of standard at present but are you sure you are reading it right? I can see that there is a need for a low speed limit for where it is in the middle of the line (otherwise a fixed distant causes all trains to brake unnecessarily and drivers could get incautious as the starter is "always off"), but approaching a terminus is to my mind completely different. We only give yellow into bufferstops nowadays!
Obviously for AHBC you don't technically need a protecting signal, but you do need a "10 minutes running time" signal to stop a train in emergency. On an OTW-NS line there is no requirement (unlike for TCB) to have a signal "at point of reversal"; however because of the crossing I would provide a STOP board in the position of a platform starter requiring driver to contact signaller before starting on return trip. I accept that may have to ensure all drivers issued with a mobile phone / have degraded mode instructions about what to do if can't make contact (e.g. travel cautiously and stop short of crossing and use phone there; only problem with that is barriers would be down for a long time and the crossing may indicate failed- at least not thinking of an ABCL where the crossing could time out and barriers rise just as train wants to cross....). Anyway, put a brief note- it shows the examiners that you know there is an issue and you have thought about it.
Trying to think where OTW-NS is in use- can't think of anywhere used with a particularly high line speed but know of no limit. Sure used at least at 40mph; don't think you need a speed restriction approaching terminus.
You are right that showing TPWS OSS in this case is sensible (whereas wouldn't expect usually on IRSE layout - just cover by note). I think that there is sometimes a blue monitor light that the driver is supposed to observe in vicinity of bufferstops themselves if they are electrically lit- though I do know of one site when miles and miles of cable was laid just to bring such an indication back to "civilisation" (stupid in my view).
Of course once we have GSM-R coverage and FTN everywhere such issues may go away.
PJW