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Post by dw54 on May 6, 2009 23:11:39 GMT
This is a question from a signalling/safeworking "layman". My terminology is quite probably imprecise.
I have two linked questions for this thread, and two for another thread.
Are participants here aware of any use made by, or consideration given by LU to use of "microblock" signalling and/or "following on" procedures?
Explanations: Some methods of "moving block" signalling are described as actually being fixed block but approximating to moving block because the block sections are very short: "microblocks". My question relates to one of the major reasons resignalling with moving block helps increase line capacity is by reducing headway, thus increasing frequency. In essence, as soon as a train moves, it creates a buffer behind it into which a following train can move. Under fixed block signalling, the following train cannot move until the preceding train has fully vacated that signal block (eg a platform road). So, if a following train can start moving into the space vacated by the first train beginning to move off the platform, quite clearly a closer headway can be maintained.
In conventional block signalling, there is provision made for "calling on". This normally involves a train entering a signal block already occupied by a stationary train. I've used the term "following on" to expand this concept to a train following a moving train into a signal block. If we think of a bus lane, where a line of buses is held at a red traffic signal, then they get the green. All the buses pull away, gradually increasing the gap between themselves as they accelerate. We don't just let one bus go at a time! So, the first question is whether anyone in the LU hierarchy has examined this "following on" concept as a means of reducing headway and thus raising line capacity?
Now when we come to rail operations, the safety aspect would direct our thoughts beyond formal "on sight" rules and speed limits to mechanical supervision with signals and train stop trip cocks.
AIUI, in order to appropriate the bulk of the benefit resignalling to moving block would give, one would need to install microblock signalling at those stations whose dwell times are critical to line capacity, and one or two standard signal blocks preceding, likewise for flat junctions and points of convergence. Such microblock signalling, I would have thought, would involve use of a standard signal type, perhaps a shunting signal (standard spares and wiring), and standard train stops. In stations, the microblocks might be just one car long, while the blocks preceding might be broken down to (eg) 1/4 blocks or 40m sections. This is just a flavour. The smaller the microblock block, the greater the frequency increase. This is balanced by the cost of adding each microblock. Someone would need to work out an optimising formula.
So, I am asking whether the players who constitute LU these days have looked at applying the principle of microblocks but with existing, tried, tested, proven hardware with which the maintenance teams are familiar and have stocks of parts and an established re-order process? Likewise, these are standard devices familiar to line operators, drivers and other staff.
All I have alluded to here relates to risk - I'm asking if anyone in the LU management process has looked at a negligible risk, low budget, rapid response method of appropriating the bulk of the benefit of moving block signalling without the "mating elephants" gestation time factor?
I do recognise that a change to modern moving block systems means many of the maintenance-intensive electro-mechanical devices (such as train stops) are replaced by no-maintenance solid state systems and digital comms. What I have outlined can only be a stop-gap measure ... but with the Olympics coming up, and SSL re-signalling deliberately left till afterwards ... this may be a "tactical response" to achieveing higher capacity on the SSL in the interim.
Anyone?
Cheers
David in Perth, Western Australia
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mrfs42
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Post by mrfs42 on May 7, 2009 7:45:28 GMT
A sensible suggestion, though sadly I don't think that there would be time to get application approval through the HM Railway Inspectorate before the Olympics. Although off the top of my head, there seems to be some similarities between what you are suggesting and Seltrac (which *is* going through a rather difficult birth[1] on the Jubilee). I trust you are aware of the older multi-home installations that still abound, there some details here on tubeprune's rather fab site. With all the headway splitting signals on the approach to stations; I have a reasonable suspicion that these will largely still be here come the Olympics. The trouble with implementing the 'microblocks' is positional references. 'Conventional' ATO-equipped lines are signalled throughout, so onboard telemetry equipment 'knows' where the train is going and how fast the train is getting there. Your rather likeable idea of 'microblocks' - i.e localised ATO would be very tricky to implement without installing absolute position reference balises. I would suspect that if this suggestion had been examined (I don't know if it has or hasn't) there would be a lot more attention paid to the VOBC (Vehicle on Board Computer) working out where it is and the speed profile that it can use then lying idle as the train passes through normally signalled areas. I think too, that the HMRI would take a very dim view of this mixed working, needing all sorts of risk mitigation and ALARP protocols applied to each site. I must admit, I like the suggestion, but to use it as a 'headway splitter' I suspect that in the long-run still be cheaper to put in the old maintenance-hungry signals, unless of course you are getting a brand new fleet of trains that can 'talk' to balises. [1] As the story goes, the cable specifications for the track loops were changed in the process of laying the cable, so it now has to be relaid to the revised specification. |
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Deleted
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Post by Deleted on May 7, 2009 9:39:03 GMT
The problem with "microblocks" is that you need a lot of extra signalling equipment (such as track circuits) to improve the signalling headway. This is expensive to install, maintain, and increases the risk of signal failure.
Modern CBTC simply requires wayside computers handling large sections of track, and onboard computer, radio transmitters & receivers. No extra equipment needs to be installed whenever you need to improve the signalling headway (within it's limits).
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Post by dw54 on May 7, 2009 16:28:16 GMT
My suggestion of microblocks was purely using OLD technology, indeed limited to existing standard stores items. Seltrac is a true moving block system AFAIK. I'm only suggesting putting in microblocks, multi-homes or headway splitting signals - whatever we call them at locations where there would be a dividend in line capacity. Yes, it would be involve extra gear, with a cost. That's why I suggested an optimising formula to work out the best number of sub-blocks to break each one into to get the maximum usable result from the least investment. The other thing is, if shunting signals were used as the physical form, and train stops (for trip cocks) used, as these are current standard devices in the signalling system, why would a reference to HMRI be involved?
Once ATP/ATS/ATO is implemented under the SSL or other line resignalling, the manual sub-blocks cease to function along with all the other signal and track circuit blocks. IMHO a wise man would keep them connected, operational but switched out along with the rest of the "old" system, but able to throw the switch - just in case!!!! I bet the retired Line Manager from the Central wishes he could have done that - just requisitioned the 62ts up from the back roads of the depot and, "whooshka, no worries folks, we have got youse a railway"!!
Cheers David
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mrfs42
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Post by mrfs42 on May 7, 2009 17:04:30 GMT
Well, in that case the opitimising formula exists and has been in use for years, albeit in its component parts:
1. calculate headway.
2. calculate overlap.
3. calculate sighting distance.
Feed into an excel worksheet and you end up with a set of figures that match the calculations for multi-home stations.
If you are going to add the 'inch' facility are you seriously suggesting a disc signal for each microblock? Now you've amplified your question a bit, you must therefore be suggesting bringing back the old calling-on and warning discs? Saving what? 5 or 10 seconds, perhaps. (this is a semi-educated guess).
Gosh, the cabling costs back to Regulators desks alone would be pretty expensive! Not to mention the reprinting and training costs of new chunks to the rule book.
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Post by railtechnician on May 9, 2009 8:35:03 GMT
Well, in that case the opitimising formula exists and has been in use for years, albeit in its component parts: 1. calculate headway. 2. calculate overlap. 3. calculate sighting distance. Feed into an excel worksheet and you end up with a set of figures that match the calculations for multi-home stations. If you are going to add the 'inch' facility are you seriously suggesting a disc signal for each microblock? Now you've amplified your question a bit, you must therefore be suggesting bringing back the old calling-on and warning discs? Saving what? 5 or 10 seconds, perhaps. (this is a semi-educated guess). Gosh, the cabling costs back to Regulators desks alone would be pretty expensive! Not to mention the reprinting and training costs of new chunks to the rule book. Not only that but some of what David focusses on has existed for yonks anyhow. A case in point being the multiple home signals and the shortened starting signal overlap which indeed allow trains in close proximity to move forward simultaneously as per his 'follow on" thoughts. I believe the concept of increasing throughput at stations was optimised on the Northern line where as many as five home signals could be found at some sites but it has been said that two homes and a starter at many sites on the Piccadilly was actually better! In this regard the Victoria line has to be best in terms of headway allowing the minimum safe distance between trains at all times as long as there are enough trains timetabled to demand it. |
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North End
Beneath Newington Causeway
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Post by North End on May 9, 2009 12:20:46 GMT
Well, in that case the opitimising formula exists and has been in use for years, albeit in its component parts: 1. calculate headway. 2. calculate overlap. 3. calculate sighting distance. Feed into an excel worksheet and you end up with a set of figures that match the calculations for multi-home stations. If you are going to add the 'inch' facility are you seriously suggesting a disc signal for each microblock? Now you've amplified your question a bit, you must therefore be suggesting bringing back the old calling-on and warning discs? Saving what? 5 or 10 seconds, perhaps. (this is a semi-educated guess). Gosh, the cabling costs back to Regulators desks alone would be pretty expensive! Not to mention the reprinting and training costs of new chunks to the rule book. Not only that but some of what David focusses on has existed for yonks anyhow. A case in point being the multiple home signals and the shortened starting signal overlap which indeed allow trains in close proximity to move forward simultaneously as per his 'follow on" thoughts. I believe the concept of increasing throughput at stations was optimised on the Northern line where as many as five home signals could be found at some sites but it has been said that two homes and a starter at many sites on the Piccadilly was actually better! In this regard the Victoria line has to be best in terms of headway allowing the minimum safe distance between trains at all times as long as there are enough trains timetabled to demand it. There's still speed-controlled signalling with five home signals on the Northern at Oval and Waterloo n/b, plus a few other locations where there are speed-controlled home signals, e.g. Colindale n/b, Brent n/b, Stockwell n/b, Archway s/b, probably some others I've missed. Waterloo rarely gets used because trains are normally held to time at Kennington. The arrangement at Oval is VERY effective in the morning peak, though this relies on drivers using it in the way it is designed, which requires a lot of nerve, a decent understanding of how it works, and a LOT of concentration. If the driver gets it right, he can be entering the platform at Oval with the rear of the previous train almost still in the platform. Always raises strange looks from passengers waiting on the platform! Get it wrong and it's a guaranteed SPAD though. |
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Ben
fotopic... whats that?
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Post by Ben on May 9, 2009 14:02:18 GMT
Slightly off topic, but are there different procedures for different levels of serious of SPADing? In the above example, it would seem perhaps less fair to throw the book at the driver when so much is demanded of him in such a section?
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North End
Beneath Newington Causeway
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Post by North End on May 9, 2009 14:32:40 GMT
Slightly off topic, but are there different procedures for different levels of serious of SPADing? In the above example, it would seem perhaps less fair to throw the book at the driver when so much is demanded of him in such a section? Not really. The current driving philosophy is that all red signals are to be treated the same, and drivers must NEVER anticipate signals clearing. In the case of Oval n/b, it's quite permissible for drivers to crawl up to each signal, and despite the fact that this will actually cause a *longer* headway than a normal location, this is what drivers are now trained to do. It takes a lot of confidence and a good knowledge of how the signals work to drive through there under reds at 25mph then 20mph. It can still be done without anticipating any signals clearing, but few drivers will do it. Of course, the first two signals are supposed to clear at 25 and 20, so a SPAD could arguably be put down to failure of signalling apparatus to work correctly. However the flip side of the coin is that a red aspect was displayed to Train Operators with enough time to stop, so technically it would still be a Cat 'A' SPAD. There's also the 5th home signal in the platform to watch out for - very easy to forget, and you can get a scenario where signals 2, 3 and 4 clear together, and the last one under the platform edge stays red. It's a very tricky layout, and IMO it merits more emphasis in training than is currently given. |
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Post by tubeprune on May 9, 2009 15:09:18 GMT
Slightly off topic, but are there different procedures for different levels of serious of SPADing? In the above example, it would seem perhaps less fair to throw the book at the driver when so much is demanded of him in such a section? Not really. The current driving philosophy is that all red signals are to be treated the same, and drivers must NEVER anticipate signals clearing. In the case of Oval n/b, it's quite permissible for drivers to crawl up to each signal, and despite the fact that this will actually cause a *longer* headway than a normal location, this is what drivers are now trained to do. Yes, this is a waste of the equipment but no one cares much now since it is all going to be binned with S40 being installed. BTW, S40 is actually a "micro block" system, using 25m long loops as positioning points. I'm afraid it's not real moving block, despite what Thales would have us believe. Agreed. I used it when it was provided on on the Picc and District. Most stations equipped with it had six home signals with 25 and 20 approach signs on the first two. At Green Park EB it was 20 and 5mph. You could approach with your eye on the 3rd signal as the stopping point and the first two would clear as you slowed on the approach. You had to do this on the stock without speedos anyway. Yes "All this side of the signal is yours; the other side belongs to the company and they don't like trespassers". Yes, there were some drivers who would crawl out of the station causing the last signal to remain on and catch you out. The one at Holborn WB was just a trainstop - no signal - so when you got caught on it, you had to get out to reset over the pit with a full audience of curious passengers. It is very important that all trains should accelerate out of the station as fast as possible in order to allow the next train to get in. They spend a lot of money on expensive kit to enable the train to do this. Don't waste it! Agreed. I don't think there are many left in LU who actually know what it's for. |
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Post by tubeprune on May 9, 2009 15:15:20 GMT
Well, in that case the opitimising formula exists and has been in use for years, albeit in its component parts: 1. calculate headway. 2. calculate overlap. 3. calculate sighting distance. Feed into an excel worksheet and you end up with a set of figures that match the calculations for multi-home stations. And don't forget train length and approach speed - but the throughput of trains ultimately depends on other factors like the dwell time. We've discussed this in other threads, haven't we? Don't forget the Victoria Line - every station is signalled for a 120s operating headway but Brixton prevents any more than a 126s headway, so the optimium service is only 28.5 trains per hour. |
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North End
Beneath Newington Causeway
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Post by North End on May 10, 2009 17:26:01 GMT
Not really. The current driving philosophy is that all red signals are to be treated the same, and drivers must NEVER anticipate signals clearing. In the case of Oval n/b, it's quite permissible for drivers to crawl up to each signal, and despite the fact that this will actually cause a *longer* headway than a normal location, this is what drivers are now trained to do. Yes, this is a waste of the equipment but no one cares much now since it is all going to be binned with S40 being installed. BTW, S40 is actually a "micro block" system, using 25m long loops as positioning points. I'm afraid it's not real moving block, despite what Thales would have us believe. Agreed. I used it when it was provided on on the Picc and District. Most stations equipped with it had six home signals with 25 and 20 approach signs on the first two. At Green Park EB it was 20 and 5mph. You could approach with your eye on the 3rd signal as the stopping point and the first two would clear as you slowed on the approach. You had to do this on the stock without speedos anyway. Yes "All this side of the signal is yours; the other side belongs to the company and they don't like trespassers". Yes, there were some drivers who would crawl out of the station causing the last signal to remain on and catch you out. The one at Holborn WB was just a trainstop - no signal - so when you got caught on it, you had to get out to reset over the pit with a full audience of curious passengers. It is very important that all trains should accelerate out of the station as fast as possible in order to allow the next train to get in. They spend a lot of money on expensive kit to enable the train to do this. Don't waste it! Agreed. I don't think there are many left in LU who actually know what it's for. Sounds about right. There are Instructor Operators who teach trainees to "wait for all the home signals to clear before moving". What do they think they're there for? |
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Post by d7666 on May 11, 2009 11:51:26 GMT
Taken to extreme analysis then yes, there is always a finite resolution at which point a mini block may be argued to exist.
But may I comment on some detail.
Positioning resolution is actually 6.25 m not 25 m.
To explain this, I need to point out it is not the ''loop'' that is 25 m long. Loops are on average 1 km long. (Further info, there are 5 VCC for the Jubilee, each VCC may handle up to 32 loops. I do not know how many loops are configured on each VCC).
The 25 m interval you refer to is the ''loop crossover''. For anyone that has not seen this, look in the four foot along the Jubilee and you will see two parallel cables either side of the conductor rail that swap sides every 25 m. This side swapping causes a signal change allowing detection of train position.
However, within each ''loop crossover'' there are four equally spaced ''positions'' i.e. every 6.25 m. Train position in each ''position'' is determined by on-train tachometers (and accelerometers).
The mini-block [to use this term] is a ''track'' - each ''track'' is made up of minimum one ''position'' - and usually but not always does equal one ''position''.
So if one must use the term ''mini block'' it is 6.25 m not 25 m.
--
Nick
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Post by tubeprune on May 11, 2009 17:28:33 GMT
OK Nick, I take your point about the 6.25m positioning but the track based detection is at the 25m crossover points. Until we get true, radio based moving block, with no track mounted loops, we are still looking at micro blocks.
Interestingly, I had a conversation with someone high up a few months ago who said, "We don't want any more of those loops strewn all over the track, thank you" when I suggested S40 might be the preferred option for SSL so it could interface with the Jubliee and Picc where necessary.
As far a the whole "Alcatel" system is concerned, it is very crude, as anyone using Docklands will know when the train lurches from motoring to coasting or braking with loud clonks as the bogies take up the strain.
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Post by d7666 on May 11, 2009 19:04:49 GMT
OK Nick, I take your point about the 6.25m positioning but the track based detection is at the 25m crossover points. Until we get true, radio based moving block, with no track mounted loops, we are still looking at micro blocks. In the sense that Seltrac S40 loops transmit track to train and receives train to track control data, it is analogous to a leaky feeder radiating cable. When it comes down to detection and resolution of train position there would almost certainly be some division into discrete blocks with a radio leaky feeder or trackside balise based radio CBTC system, leaving fine positioning to train borne kit. The fine positioning of Seltrac S40 is down to 5 cm - course notes tell me can get wheel positioning to 1.2 cm. I presume these values could be theoretically usable for blocks - but the value of doing that is probably negated when compared with safety overlaps for fail-safe seperation. I am not sure but I think both Bombardier CityFlo and Alstom Urbalis work to a coarse trackside and fine on-train resolution. The equivalent Siemens moving block system is like Seltrac ... digressing ... actually Siemens devised in the 1960s for DB the technical basis of what is now Seltrac. Originally devised for +160 km/h high speed lines, LZB used long loop cables that cross over at 100 m intervals. Those who state moving block is a new system don't like having it pointed out  that S40 origins are actually the same vintage as A60/A62 stock, and is older than the Vic.line 1967 ATO, as it was tested in service in 1963. If you ever get a chance take a look at a VCC cabinet ... they are marked LZB (Linienzugbeeinflussung) ... which is exactly where it came from.
That possibly depends on from what viewpoint one looks at this. Cables in the four foot and/or suicide pits are messy and in the way of all activities from simple track walking to site to track repairs. But there are certainly those who favour S40 for SSL.
Don't get me wrong, I am not arguing in favour of Seltrac - I am merely one who is VCC trained - just trying to put out a balanced view.
All this reminds me I must pester a contact on DB Munchen S-bahn to go and look at their LZB. In 2004 they put in LZB over the central ''stammstrecke'' section for 30 TPH.
--
Nick
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Post by tubeprune on May 11, 2009 19:55:50 GMT
I was aware of the German origins. Wasn't the SEL part of Seltrac, Standard Electrik Lorenz?
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Post by d7666 on May 11, 2009 20:38:28 GMT
I was aware of the German origins. Wasn't the SEL part of Seltrac, Standard Electrik Lorenz? Ja, genau. -- Nick |
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Post by dw54 on May 14, 2009 12:02:41 GMT
Thanks to those who posted about multiple homes. I'm a little confused. Did they allow a train into a platform even while the preceding train was still in it, but moving out? ie the signal blocks were shorter than a train through that platform.
And yes, I did have in mind individual shunting type signals (are they lamps at 45 deg, or an electro-mechanical disk?) with train-stop, and some cabling back to the control centre. I had in mind to use equipment which had a standard meaning, to minimise location specific instructions for the manual. The intention is that trains enter the platform when the departing train has cleared perhaps 1/4 train length of platform.
Of course, the Victoria Line ATO would have capabilities to do this. I was looking for a stop-gap that could be used to ramp up capacity ahead of wholesale resignalling, and perhaps improve performance at some bottlenecks prior to the extra traffic load of the Olympics - which will probably be happening at the same time as the wider economy wakes up.
My 2p
David down under
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Ben
fotopic... whats that?
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Post by Ben on May 14, 2009 12:56:19 GMT
The signal blocks were shorter than a trains length in some places. Q8 once remarked that near Mansion House if there was blocking back along the line the guard, if in the rear cab, could converse with the driver of the train behind!
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Post by Harsig on May 14, 2009 13:01:30 GMT
Q8 once remarked that near Mansion House if there was blocking back along the line the driver could have a conversation with the guard of the train in front if he were in the rear cab! If the driver was in the rear cab of the train in front then perhaps he stopped his train just a little too close for comfort ;D or is that not quite what you meant |
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Ben
fotopic... whats that?
Posts: 4,282
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Post by Ben on May 14, 2009 13:05:29 GMT
*clears throat* Ooooh, look over there!  ;D |
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Post by tubeprune on May 15, 2009 4:55:50 GMT
Thanks to those who posted about multiple homes. I'm a little confused. Did they allow a train into a platform even while the preceding train was still in it, but moving out? ie the signal blocks were shorter than a train through that platform. No. I think this link will explain the system: www.trainweb.org/tubeprune/signalling4.htm |
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that S40 origins are actually the same vintage as A60/A62 stock, and is older than the Vic.line 1967 ATO, as it was tested in service in 1963. If you ever get a chance take a look at a VCC cabinet
;D
