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Post by Admin Team on Apr 19, 2005 19:24:41 GMT
Firstly, my apologies to the non-LU staff who contribute to and read this forum for what I suspect may end up being a bit of a 'techie' item, but I hope it will prove of interest nonetheless. In the thread 'Dodgy Signals' which can be read at districtdave.proboards39.com/index.cgi?board=District&action=display&thread=1113162306 a number of factors have been raised, which may have good technical explanations but which, in a day to day sense, don't make a driver's life easy. Additionally, there are various anomalies which 'we' encounter which I'm sure would be easier to cope with, if we understood 'why'! 1) This first is a 'general' question (and probably the longest!). Irrespective of our grade in LU we all do 'OPT' (Operational Procedures Training - what used to be Rules and Regs) and all do a bit of theory about the siting of signals. The general rule of thumb about the siting of a signal is that it revolves around a 'braking distance' and that this depends on a number of factors:- a) The speed of the fastest train that will use the area b) The weight of the heaviest train that will use the area c) Gradient d) Braking capacity of the train This theory then extends into other areas such as line capacity, information & visibility (siting distances, weather conditions) and timetables. Now, that's all well and good, and if adhered to by (I presume) the designers, I'm sure it'd all be great. Why then do there seem to be enormous inconsistencies in where signals are located? I'm sure I'm not alone in thinking that the engineers actually work on an 'oh, this is a nice place - I think I'll put this signal here' basis. Is any account taken of matters such as 'curves' and 'gradients' which do have more than a little bearing on the TRUE visibility of any given signal? 2) When repeaters are located, is there supposed to be some consistency in their distance from the signal to which they relate? 3) On a couple of District Line matters - can someone explain the following: a) (aetearlscourt, I know you've explained this to me, but for the benefit of others, have another crack).... The draw up signals at Whitechapel Platforms 1,2 & 3 of course have associated trainstops, all of which 'drop' very slowly. Why is this? b) Signal OB44 (e/b road between Aldgate East and Whitechapel) should (by all logic) be a shunt signal, as it signals trains back into the w/b platform at Aldgate East. Why then is it a coloured light signal? The only thing I can work out is that where it's located is very tight space wise, and perhaps a 'traditional' shunt signal won't fit? 4) And finally (hear's sighs of relief!) mention is made on the thread referred to above of OP38. I'm sure many of the problems relating to this signal could be overcome by the siting of it's repeater on the previous signal. Hasn't this occured to anyone? And given the cost that delays through SPAD's cause would not this actually save revenue? Look forward to the replies! |
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Post by citysig on Apr 19, 2005 19:47:00 GMT
I have a couple (I hope)
3a) They are normally slowed on purpose. An extra length (or sometimes referred to as a "slug") of air hose is put in to slow the air reaching the trainstop. This means the stop will lower somewhat slower and provide just that extra bit of safeguard, and means you would have to maybe slow to slightly lower than the "booked" speed before the trainstop lowers fully. It takes into account the less-accurate deltas used. Many re-signalled areas have more accurate position detectors installed, and therefore do not require this exta "slack."
3b) There are many signals like this believe it or not. They are exceedingly helpful during shutdowns. Picture a total shutdown at Whitechapel, and yourself standing between Aldgate East and Whitechapel with a train full of passengers. If it was an ordinary shunt signal, we couldn't simply bring you back to the platform at Aldgate East. Having a running signal means we can.
Other examples exist at Swiss Cottage (Met disused) Aldgate (just after leaving on the westbound) and just north of Neasden on the northbound Met an Jubilee.
4). I attended the original meetings concerning the re-signalling in the 1990s. Many of the signals were to have been changed/re-sited etc. OP38 was, as far as I can remember, one of those to be looked at. OP36 was another. However, as usual, the program ran over-budget and over-time, and much of the planned alterations to signalling - both outside and in the cabin - were never carried out. Many of the station starters were moved "into the canapy" and I'm not sure if this improved things or not. Certainly meant any relamp had to be carried out in engineering hours, or with lots of protection during traffic.
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Tom
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Post by Tom on Apr 19, 2005 20:17:03 GMT
Hopefully I can provide an answer to some of your more general questions from a signalling design background...
Sighting distance for a signal is calculated to give six seconds sighting at line speed then a braking sistance to stop. The formual uses is (v2+u2/2a) + 6u = s
Where u = initial velocity (line speed, taken from train performance curves) v = final veclocity (0), a = deceleration (again taken from the train performance curves) and s = the sighting distance.
From what my little book of no knowledge is indicating to me, gradient and train loadings don't come into it, the idea being that a train operator should already be obeying the maximum line speed and the distance required to brake for the signal shouldn't change as long as he/she is at the correct speed.
However, overlaps do take into account gradients, and in particular they look at the gradient over the last 65m on the approach to a signal and throughout the overlap. 'How does an overlap formula already know the overlap?' I hear you ask. The simple answer is you do a rough calculation using a simplified formula to estimate the length of overlap needed assuming certain characteristics such as braking performance. (Or you get MS Excel to work it out for you).
Signals are located at specific places to enable the specified headway, as specified by LU, to be achieved, taking into account a couple of datum dimensions, like the platform track circuit must start 50 feet in rear of the ramp, and the overlap of the home (or first home) must end at the 50' blockjoint. If the signal is on a curve, repeaters are positioned in order to maintain the sighting distance for the required six seconds, and they are normally as close to the signal as possible to meet the required sighting time.
If problems are highlighted post-commissioning, a repeater can be added or a signal moved to suit local conditions a little better. An example of this is on the NB bakerloo between E&C and Lambeth North, where a repeater (RBR15) had to be added after commissioning as the main signal BR15 wasn't as visible as first thought.
I hope that goes some way towards answering your questions and hope it doesn't look like I'm spouting bullsh*t.
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Post by Harsig on Apr 19, 2005 20:43:57 GMT
I have a couple (I hope) 3b) There are many signals like this believe it or not. They are exceedingly helpful during shutdowns. Picture a total shutdown at Whitechapel, and yourself standing between Aldgate East and Whitechapel with a train full of passengers. If it was an ordinary shunt signal, we couldn't simply bring you back to the platform at Aldgate East. Having a running signal means we can. Other examples exist at Swiss Cottage (Met disused) Aldgate (just after leaving on the westbound) and just north of Neasden on the northbound Met an Jubilee. Amplifying on this a bit, Shunt signals for moves between running lines seem to have fallen out of favour at some point prior to the resignallings that took place in the 1980s. The Aldgate area (resignalled 1988)for example has no shunt signals at all. Citysig has already mentioned the similar examples at Neasden, another 1980s resignalling and here the only shunt signals provided are for moves to and from depot. In fact of the 1980s signalling in the area controlled by the SCC the only examples of shunt signals being provided to cross between running lines that I can think of off the top of my head are MB33 at Baker St (Outer Rail to platforms 2,3 & 6) and JD12 at Finchley Road (NB Jubilee to platforms 1,3 & 4). In both cases one or more of these signals' routes is against the normal direction of travel of the platform concerned and this may be the reason a shunt signal was provided. Alternatively it may simply be because they have more than one route. [Before anyone says anything the signalling between Kings Cross and Liverpool St, which does have a number of shunts signals for moves between running lines, is iof significantly earlier vintage than the signalling at Aldgate and from Baker St northwards.] As to why shunt signals may have fallen into disfavour it is certainly the case that from a technical point of view it is simpler to provide a a running signal than a shunt signal as shunt signals have to be proved in a similar way to trainstops and because they contain moving parts they are presumably more demanding of maintenance than a simple colour light signal. |
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Post by Harsig on Apr 19, 2005 21:06:10 GMT
Alternatively it may simply be because they have more than one route. The more I think about it the more I feel that the reason MB33 & JD12 signals are shunt signals is indeed because they have multiple routes. The reason being that as far as I am aware the vast majority of such signals are ground mounted and there would be a problem providing Harbour lights on such a signal, not least the lack of room at ground level. I'm led to understand that providing a theatre type route indicator on a colour light signal would contravene LUL signalling principles as they stand at present. This came up in discussion as to how to indicate all possible routes on signal OB2 at Aldgate. For those who don't know OB2 is the inner home signal for trains coming from Liverpool St and is the signal which indicates which route is set i.e. to Aldgate East or Aldgate platform one, two or three. The problem here is that there are two possible routes to platform 1 and two possible routes to platform 2 but there is no indication to the driver as to which route has been signalled and so one of the possible routes in each case is suppressed so that it will not be used in normal operation. The discussion centred on how to modify the signal so that each route was uniquely identified and of course one possibilty that was looked at was providing a theatre type route indicator for the signal which was when it was discovered that this arrangement does not exist on the underground and so all sorts of type approvals would have been neccessary before the modification could be made. Incidentally with all the variations of route that can be achieved OB2 has six routes. Are there any other colour light signals on the underground with as many or a greater number of routes. |
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Deleted
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Post by Deleted on Apr 19, 2005 22:10:09 GMT
Why would so much nonsense be needed to fit an LED route indicator to OB2 at Aldgate? You could set it up like the ones on NR signalling systems and number it thus (based on this diagram): www.pryan.org/mozilla/site/TheOneKEA/misc/triangle_layout.txt1 - Aldgate East (via 1, 2, 3 pts) 2 - Aldgate pfm 1 (via 1, 2, 3, 4 pts) 3 - Aldgate pfm 1 (via 1, 2, 5, 4 pts) 4 - Aldgate pfm 2 (via 1, 2, 5 pts) 5 - Aldgate pfm 2 (via 1, 9, 8, 5 pts) 6 - Aldgate pfm 3 (via 1, 9, 8, 6 pts) 7 - Aldgate pfm 4 (via 1, 9, 8, 6, 7 pts) (Note that this probably has no bearing on reality  ) |
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solidbond
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Post by solidbond on Apr 19, 2005 22:38:23 GMT
The more I think about it the more I feel that the reason MB33 & JD12 signals are shunt signals is indeed because they have multiple routes. The reason being that as far as I am aware the vast majority of such signals are ground mounted and there would be a problem providing Harbour lights on such a signal, not least the lack of room at ground level. I'm led to understand that providing a theatre type route indicator on a colour light signal would contravene LUL signalling principles as they stand at present. However, if you think about Aldgate, and the signal that Citysig mentioned, to reverse a train which is west of Aldgate, back into the O/R or the 2 bay platforms, that uses a route indicator, the same as used on MB33 at Baker Street, ie backlit numbers in a box. For those who don't know what I mean, it is a box with 4 possible positions, and each position has a lens with a number in it, and a bulb behind it. However, you can only see the number when the relevant bulb is lit. This differs from a Theatre Type Route Indicator, which uses 49 bulbs in a box, and illuminates a number of them to display a number from 1 - 19 using multiple bulbs! (I hope this makes sense - it is late  ) |
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Post by Deleted on Apr 19, 2005 22:57:57 GMT
only answering about the speed control at whitechapel ;D ;D ;D
the trainstops are effectly speed control trainstops which protect the junction in front of the station starters as the points are too close. how they actually work is this instead of additional circuits its simply done by instead of feeding the trainstop directly to the valve like any other signal this is done by feeding another bit of air main pipe then to the trainstop thus taking longer to fill the pipe with air thats why the trainstop lowers very slowly and thats why you get a dual aspect which seems to be forever
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Deleted
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Post by Deleted on Apr 19, 2005 23:04:49 GMT
also dave about the actual siting of signals this was done many years ago when older surface stock was around why do think there is so many comprimised signal overlaps (speed restrictions) its because they got worried that if a train was going at top speed and it was wet and the brakes wasnt that good that it could run into the back of another train if he/she tripped past the signal.
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Colin
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Post by Colin on Apr 20, 2005 1:46:52 GMT
Expanding on the original question slightly, why is there a long gap between signals from Dagenham East to Elm Park Eastbound. And why do all the signals clear together between Upney and Becontree Eastbound. It's a pain in the rear when you're close to the train in front!  |
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Post by q8 on Apr 20, 2005 4:00:22 GMT
 To answer Colin's question :- I thinks it's a tacit admission that the brake on "D" stock is a lousy effort in that having only one block per wheel for the friction brake is not near as good as having two like the older stocks did. With the older stocks you could run full speed into Becontree eastbound and aplly the brake at the platform ramp and still ahve to partial release before you got to the stop mark. Even with an R stock. Can you do that with a "D" 
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Post by Deleted on Apr 20, 2005 4:46:32 GMT
To go back to the Whitechapel draw-up trainstops again for a moment...
As explained, and is perfectly obvious, they are there to reduce the risk of a driver running the signal and therefore compromising the points, however IMHO they are a bit pointless in that they are so slow to drop that you have to apply power again to reach the end of the platform!!
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Post by piccadillypilot on Apr 20, 2005 6:53:34 GMT
they are so slow to drop that you have to apply power again to reach the end of the platform!! Is there anything to prevent a slower approach? The really sneaky draw-up that I recall is at Stockwell s/b. The station being on a hump you can't see either the draw up nor the starter until you're almost in the platform. |
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solidbond
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Post by solidbond on Apr 20, 2005 7:29:47 GMT
Is there anything to prevent a slower approach?. Ahh - but Whitechapel is on a hump as well, so if you approach slower, you will come to a gentle halt and roll back, unless you apply power, so that wouldn't work either |
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Post by citysig on Apr 20, 2005 8:57:09 GMT
the trainstops are effectly speed control trainstops which protect the junction in front of the station starters as the points are too close. how they actually work is this instead of additional circuits its simply done by instead of feeding the trainstop directly to the valve like any other signal this is done by feeding another bit of air main pipe then to the trainstop thus taking longer to fill the pipe with air thats why the trainstop lowers very slowly and thats why you get a dual aspect which seems to be forever That's kind of what I tried to say, but I was rushing to leave work at the time and you are the technical chap so I leave it to you. Just to clarify what I meant though. They are not slow to slow you down more. They are slowed to prevent the signal clearing before you have slowed. Confused? Older signalling equipment would, effectively, give a clear signal too soon - when maybe you were still a few mph above the limit. Slowing the trainstop takes account of this older equipment and gives those extra couple of seconds before a clear is shown. Nothing to do with gradient. More to do with equipment installed. I think one of our learned colleagues will confirm that the same is done on certain sets of points with WLs? It slows their throwing to give everything a chance to lock. Hammersmith (H&C) is an example. |
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Post by piccadillypilot on Apr 20, 2005 9:13:42 GMT
Ahh - but Whitechapel is on a hump as well, OK, understood. A classic case of whatever one does, it's wrong by the sound of it. |
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Post by Deleted on Apr 20, 2005 9:28:00 GMT
your correct sometimes in certain areas the points are slugged due to the fact the WL actually beats the points so what they do is have a nice short hose on the WL but have longer hoses on the actual air hoses to the point motor (air cylinder) the site that springs to mind of this is West Kensington the set that is in the platform at the west end of the station (sorry cant remember numbers ) also some sites they slug the actual lever motor if i remember rightly dagenham east is like this
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Post by q8 on Apr 20, 2005 10:52:40 GMT
Can I poke my oar in (cries of "oh Gawd not again") There is an overbridge in the tunnel between Stepney Green and Whitechapel about halfway between Stepney Green advance and the first Whitechapel home (It's a bit hard to see in the dark but it is there) Give the old jalopy FP from Stepney 'til the bridge in the tunnel is reached and then coast. You should have enough oomph to get you up the slope at Wcpl and see the sentry clear and get to the car mark without having to motor again. Similarly when leaving Bromley-by-Bow westbound. Full handle until the advance starter is got to and then coast. Again enough momentum to get you round the bend without jerking and down the hill. That's how we judged speed without a speedo......Worked in the old days anyway.
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Post by q8 on Apr 20, 2005 11:15:26 GMT
If I understand the explanation for these slow trainstops it equates to "Fat pipe, low air pressure, slow trainstop" "Thin pipe, high pressure, fast trainstop. Correct me if I'm wrong please.
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Post by Deleted on Apr 20, 2005 14:17:25 GMT
correct
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solidbond
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Post by solidbond on Apr 20, 2005 21:56:43 GMT
Can I poke my oar in (cries of "oh Gawd not again") There is an overbridge in the tunnel between Stepney Green and Whitechapel about halfway between Stepney Green advance and the first Whitechapel home (It's a bit hard to see in the dark but it is there) Give the old jalopy FP from Stepney 'til the bridge in the tunnel is reached and then coast. You should have enough oomph to get you up the slope at Wcpl and see the sentry clear and get to the car mark without having to motor again. Similarly when leaving Bromley-by-Bow westbound. Full handle until the advance starter is got to and then coast. Again enough momentum to get you round the bend without jerking and down the hill. That's how we judged speed without a speedo......Worked in the old days anyway. Would be fine - EXCEPT - there is now a temporary 10mph restriction as you leave the tunnel mouth approaching Whitechapel - so you have no choice but to slow down, especially as it is one of the favourite spots for DMTs to use their speed gun  |
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Post by q8 on Apr 21, 2005 3:10:25 GMT
Would be fine - EXCEPT - there is now a temporary 10mph restriction as you leave the tunnel mouth approaching Whitechapel - so you have no choice but to slow down, especially as it is one of the favourite spots for DMTs to use their speed gun. Crafty, lousy, rotten, mean, miserable b*astards.  |
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Colin
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Post by Colin on Apr 21, 2005 19:03:39 GMT
To answer Colin's question :- I thinks it's a tacit admission that the brake on "D" stock is a lousy effort in that having only one block per wheel for the friction brake is not near as good as having two like the older stocks did. With the older stocks you could run full speed into Becontree eastbound and aplly the brake at the platform ramp and still ahve to partial release before you got to the stop mark. Even with an R stock. Can you do that with a "D" I tried it at Becontree with a very average train and it seems to me a D stock is no worse than older types. I'm too young to have driven the older trains you mention, perhaps there's somone else on the forum with some years of experience (not meant the way it sounds !  ), who could comment better on overall performance between the types. P.S. I'm starting a new thread on my original qeustion as it wasn't totally relevant to the way this thread has developed. |
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Post by Admin Team on Apr 21, 2005 20:05:32 GMT
To answer Colin's question :- I thinks it's a tacit admission that the brake on "D" stock is a lousy effort in that having only one block per wheel for the friction brake is not near as good as having two like the older stocks did. With the older stocks you could run full speed into Becontree eastbound and aplly the brake at the platform ramp and still ahve to partial release before you got to the stop mark. Even with an R stock. Can you do that with a "D" I think it's probably correct to say that the brakes on a D aren't the greatest, but, so long as you remember this, I personally don't have an issue with them. As an example (and just in the interest of research you understand) I approached DagE w/b today at :-Xmph (answers via a PM if interested....) and applied Service 4 at the home signal. The train drew up easily by the stopping mark and did need a release to allow it to reach. But, there wasn't much 'margin for error' though. |
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