OTW & terminal platforms- 2007 layout

[mark bedford]

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

[PJW]

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

[mark bedford]

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?

PJW

Thank you for your very quick reply Peter. I'm sure I have mis-read the reference to 20mph in GK/RT0032.

There are obviously limits when to use a distant board but it doesn't come under a category 1-4 as per colour light or semaphore, a BS standard is quoted, I've found no other reference to speed. Seems a bit of a double standard if we give a free yellow at the end of a single line but delayed yellow in TCB, maybe I should look at this from the positive, that we can give even better safety with TCB.

I thought with the latest NRL2SIG30009-D310 we now have to provide a controlled signal plated passable if we have an auto crossing in the route.

So many instructions! I have missed crossing predictors, something new to look up, thanks again.

[PJW]

Thank you for your very quick reply Peter. I'm sure I have mis-read the reference to 20mph in GK/RT0032. There are obviously limits when to use a distant board but it doesn't come under a category 1-4 as per colour light or semaphore, a BS standard is quoted, I've found no other reference to speed. Seems a bit of a double standard if we give a free yellow at the end of a single line but delayed yellow in TCB, maybe I should look at this from the positive, that we can give even better safety with TCB. I thought with the latest NRL2SIG30009-D310 we now have to provide a controlled signal plated passable if we have an auto crossing in the route. So many instructions! I have missed crossing predictors, something new to look up, thanks again.

GK/RT0032 B8.5.4 effectively permits fixed distants when either:
a) all trains stop
OR
b) 20 mph or less
so basically it says what I claimed it should (i.e. RSSB agree with me!)

You do make a valid point re the category- a reflectorised distant board can certainly be less conspicuous than either a yellow light or a real semaphore distant. Generally OK on a typical rural green location but I think would get more lost in urban clutter. I think this is part of the issue; the driver has to have route knowledge to know re speed restrictions and speed signage is just reinforcing that message and saying "the restriction you already know about commences exactly here" or in the case of the triangular signs "you need to start braking for it here". Hence the distant board on approach to the terminus is really like a AWB for a permanent speed restriction of zero at the bufferstops. We seem content to use speed signage at speeds of up to 125mph don't we?

Level crossing predictors (GE HXP3) used on Cromer line and Bedford Bletchley by "Vaughan -Harmon" as was. WRSL (I think it is sister company Safetrans product) also have at least one in trial use somewhere and may well now have been approved.
Certainly defined as "the default standard" now. Actually they are great for crossings well away from stations and signals within "strike-in"; a lot of us feel that they lose a lot of their advantages when can't be so isolated. As it happens, Western section IRSE meeting this Wednesday on the WRSL product; however have been a presentations in the last couple of years at some IRSE conference (may have been a YM meeting last Nov). Some years back (perhaps as long ago as 1999) I think a Phil Davis paper introducing American technology that may cover. Otherwise try GE or WRSL websites.

Why do you say delayed Y in TCB? Only approach release an aspect into a terminal platform at a through station or a particular line in a terminus that is shorter than the rest- generally there is no approach release of the last R/Y signal giving admission to platforms at terminus.

You might be right about NRL2SIG30009-D310. If it says it, then it hadn't really thought about non TCB lines (I was on Signalling Principles Group meeting that reviewed it so feel qualified to say this!) so don't read too much into it [Note to self / Lynsey- let's check and may need to consider "clarification" when group next meets]. To be honest I think that it says something to the effect of: WHERE there is a signal that could otherwise be what we traditionally called an Auto that is prior to an AHBC, then it should be plated as NON-PASSABLE; not that there MUST BE such a signal provided- but perhaps it doesn't!

Yes there are a lot of instructions. No one can know them all. You and I have each been around for quite a time; it is difficult for others with less length and direct involvement to assimilate.

I tend to advise my students to declare their practices as UK Mainline c2000; avoids claiming compliance with all the latest ideas that may or may not have actually perculated out to affect much of the railway and probably are more in tune with what the average person encounters. If you are a maintainer for a large PSB put into service in the 1980s then may well be sensible for you to declare compliance with that environment; if you are always designing or testing modifications to Bristol say then Western Region practices on 1970ish may be what your experience is. Just declare so and signal in accordance as the rules of the exam permit you to do this. The students that I feel sorry for are those who don't really hae any experience in anything similar (e.g. different branch of signal engineering or working on a railway very different to the UK so that the layout plan itself is "foreign" to them and has things that do not feature in their environment); they have to learn from where they can, things are inconsistent from different sources as practices vary over time and place ........

Go on; give the examiners a hard time. Declare familiarity with Malaysian practice and they will have to find out what that is! Certainly they had to mark a Thai one some years back- but disappointingly it was pretty similar to BR 3 aspect signalling as based on Transmark spec. However there is a lesson there; ALL candidates should declare practices. If you don't and it looks a bit like some UK practice the assumption would have to be current day NR- therefore any "differences" will be seen as "errors". If you declare something, then it is up to the examiners to find out whether you were really following it correctly!

But don't get hung up on nuances of detail.
# Concentrate on a good level of completion- at bare minimum signal positions and aspects for entire layout and at least a significant complex area of the layout looking fully completed
# Make sure that you keep an eye on mark allocation and divide time accordingly.
# Make sure that you read all the notes and have actually implemented all the operational moves requested explicitly and implicitly needed to run the train service as described
# Don't confuse max permissible speed with headway speed
# State practices, explain assumptions

Focus on the above, not the speed at which a reflectorised distant board may be used, interesting point though it is!

PJW