Special low speed working on Sydney Underground City Railway

 
  N959 Junior Train Controller

Can anyone shed any light on the refinement dating to circa 1932 that allowed trains to enter platforms at Town Hall and Wynyard when the preceding train was only half way out of the platform but calculated to be travelling at a speed that would prevent its stopping on the platform (I'm guessing successive track circuit occupation by the departing train had to beat a speed 'calculating' timer, but have never been able to confirm any details about it). I have seen brief mention of the 'refinement' in two books, but nothing detailed, and no proper discussion of it among railwaymen or in official railway publications, so I'm looking for more information, e.g. is this arrangement still in place? etc

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  TomBTR Chief Train Controller

Location: near Sydney
I have not seen this since the trains stopped being red. However in principle, it could work wherever there are more train stops than signals. The extra stops are still there, and stilll working.
  historian Deputy Commissioner

Can anyone shed any light on the refinement dating to circa 1932 that allowed trains to enter platforms at Town Hall and Wynyard when the preceding train was only half way out of the platform but calculated to be traveling at a speed that would prevent its stopping on the platform (I'm guessing successive track circuit occupation by the departing train had to beat a speed 'calculating' timer, but have never been able to confirm any details about it).I have seen brief mention of the 'refinement' in two books, but nothing detailed, and no proper discussion of it among railwaymen or in official railway publications, so I'm looking for more information, e.g. is this arrangement still in place? etc
"N959"


All my references are packed away, but the intermediate train stops cleared off timed track circuits on the arriving train. From memory, the intermediate train stops would clear if the approaching train was travelling slow enough (proved via a timed track circuit) to be able to stop without hitting the preceding train if it tripped past the train stop.
  N959 Junior Train Controller


Can anyone shed any light on the refinement dating to circa 1932 that allowed trains to enter platforms at Town Hall and Wynyard when the preceding train was only half way out of the platform but calculated to be traveling at a speed that would prevent its stopping on the platform (I'm guessing successive track circuit occupation by the departing train had to beat a speed 'calculating' timer, but have never been able to confirm any details about it).I have seen brief mention of the 'refinement' in two books, but nothing detailed, and no proper discussion of it among railwaymen or in official railway publications, so I'm looking for more information, e.g. is this arrangement still in place? etc
"N959"


All my references are packed away, but the intermediate train stops cleared off timed track circuits on the arriving train. From memory, the intermediate train stops would clear if the approaching train was travelling slow enough (proved via a timed track circuit) to be able to stop without hitting the preceding train if it tripped past the train stop.
"historian"


What I don't get is how something like this could be absent from the rules (not only the current ones, either), which clearly state that with a Low Speed indication the line will always be clear to the next signal (as a form of reduced overlap Caution with speed control) when, in fact, that is not always the case. If this installation really exists, the only things separating trains are train stops and timing circuitry, which is all well and good, but more people should know about it. Any drivers out there know about this - are you taught it? Unless they know, I can imagine that some drivers would be reporting a signal irregularity if they got a Low Speed before the train ahead had cleared the platform.
  Ballast_Plough Chief Commissioner

Location: Lilydale, Vic
Unless the low speed indication only proved that facing points were locked but that the section ahead may be occupied?
  MILW Junior Train Controller

Location: Earth
But that would make it nothing more than a form of calling on signal. I thought it was a bit more sophisticated than that.
  N959 Junior Train Controller

Well, I suppose it is a special form of strictly controlled permissive working, whereunder trainstops become signals, in a sense. I've never heard of such an arrangement anywhere else. The automatic signals were permissive, anyway, so it wasn't actually forbidden to have two trains in the section; this supports the "calling-on" idea, but doesn't help explain exactly how it worked.

The 1932 Camden to Watford signalling on the LMS included an automatic calling-on, in the form of a subsidiary yellow (beneath a red) which cleared when the the berth track circuit of a signal was occupied for one minute and the preceding train cleared the overlap track circuit in advance of that signal. The trainstop was also lowered. However, it was sight separation after the second train entered the section. Byles or Barton went further by including engineered controls to prevent rear end collision with two trains in the section.
  Aurora8 Assistant Commissioner

Location: Sydney
My understanding is that the Low Speed works as per usual but the only difference is that you have the intermediate train stops which ensure that drivers maintain a low speed from when entering the platform to stopping at the other end. I'd say the limit past the intermediate train stops is 25 km/h as per the RailCorp's description of the Low Speed indication. I'm sure there are also intermediate train stops on the Down Shore platform at Hornsby so the same rules would apply there.
  N959 Junior Train Controller

My understanding is that the Low Speed works as per usual but the only difference is that you have the intermediate train stops which ensure that drivers maintain a low speed from when entering the platform to stopping at the other end. I'd say the limit past the intermediate train stops is 25 km/h as per the RailCorp's description of the Low Speed indication. I'm sure there are also intermediate train stops on the Down Shore platform at Hornsby so the same rules would apply there.
"Aurora8"


There is an intermediate train stop on the Down Shore at Hornsby, and at numerous other locations (Central Electric, Ashfield - Strathfield etc), but in the City Underground and ESR there are three or four along each platform. They can be seen lowering in succession after a train departs. I have seen trains crawling from train stop to train stop after passing a low speed, particularly at Martin Place, but not before the preceding train was already well and truly off the platform. The question is, was the Low Speed exhibited before or after the preceding train cleared the platform departure signal.
  Aurora8 Assistant Commissioner

Location: Sydney
Well to answer that question, I think the best chance would probably be to ask a driver who is in the best place to see this unfold.
  seb2351 Chief Commissioner

Location: Sydney

My understanding is that the Low Speed works as per usual but the only difference is that you have the intermediate train stops which ensure that drivers maintain a low speed from when entering the platform to stopping at the other end. I'd say the limit past the intermediate train stops is 25 km/h as per the RailCorp's description of the Low Speed indication. I'm sure there are also intermediate train stops on the Down Shore platform at Hornsby so the same rules would apply there.
"Aurora8"


There is an intermediate train stop on the Down Shore at Hornsby, and at numerous other locations (Central Electric, Ashfield - Strathfield etc), but in the City Underground and ESR there are three or four along each platform. They can be seen lowering in succession after a train departs. I have seen trains crawling from train stop to train stop after passing a low speed, particularly at Martin Place, but not before the preceding train was already well and truly off the platform. The question is, was the Low Speed exhibited before or after the preceding train cleared the platform departure signal.
"N959"


Low speeds have always been given once the train has cleared the platform. The idea is that the approach speed is set so that a driver doesnt go barreling into the platform and run the risk of colliding with the train whose backside might just be beyond the depature end of the platform.

The trips will go down if your doing the right approach speed. For example, P1 Bondi (no train in front) you need to aim for speed 18, 12 and 9 otherwise the trips will get you. The idea is to protect a possible train in front of you, (you approach on a low speed).

Same with all the underground stations.

  MILW Junior Train Controller

Location: Earth
Seb, that sounds like the standard Low Speed system, not the refinement at Town Hall and Wynyard. I thought the train stops were lowered based on track circuit controlled timers. There is no real active monitoring of the train's speed, just a timer based on a predetermined speed.
  mrfs42 Station Staff

Location: Caergaint
Large swathes of the UndergrounD in London were converted to speed signalling in the 1950s. Similar set-up with train stops but straight red/green (2-aspect) UK-style signalling. 

If there was any similarity between the two systems there would have been some form of inductor that gauged the speed of the approaching train using the train itself, rather than a countdown timer which is  prone to mechanical failure. The approach speed was determined as a 'rolling overlap' between the approaching and departing trains. 

I have seen small snippets of bookwirings from the UndergrounD with the general principles laid out - the only real change would be at the concatenation of the aspects at the signal head; the GRs and VCRs are broadly the same in the wiring. Typically, I can't immediately lay my hands on any of the references, although I can remember that Robert Dell (the London Passenger Transport Board's signalling whizz) patented the inductors in the late 1940s

There is more information on LU speed signalling here: http://www.trainweb.org/tubeprune/signalling4.htm and multi-home signalling, although this only really scratches the surface of the installations - the  ultimate inspiration for the UndergrounD habits came from either the IND or the BMT in New York and I have seen mention of the Sydney installation too. 

There are also locations where there were signal-less train stops controlled by inductors. 





  mrfs42 Station Staff

Location: Caergaint
This is a picture of an UndergrounD inductor: http://www.flickr.com/photos/27565507@N06/3804313034/ - It measures the speed of a train passing over it by the shoes generating a small AC signal in magnets hidden in a dummy bit of conductor rail. The frequency generated is proportional to the train speed, hence the ability to measure speeds.

If the Sydney installation used the speed of the trains themselves in such a manner, I'd be interested to find out a bit more. 

  raymcd Locomotive Driver

Location: Artarmon NSW
This is a picture of an UndergrounD inductor: http://www.flickr.com/photos/27565507@N06/3804313034/ - It measures the speed of a train passing over it by the shoes generating a small AC signal in magnets hidden in a dummy bit of conductor rail. The frequency generated is proportional to the train speed, hence the ability to measure speeds.

If the Sydney installation used the speed of the trains themselves in such a manner, I'd be interested to find out a bit more.
"mrfs42"


Getting back to the original question:
Harking back to my days 50 years ago as signal electrician; I recall that the intermediate train stops would stop a train if it exceeds 17 mph after passing a low-speed indication (R/R/G) because the low-speed indication has reduced overlap. This is effected by a time delay relay on the preceding track circuit which is set to release the trip arm after the train has been on the track circuit for the set time. The set time is calculated from length of track circuit divided by the the maximum speed. It follows that if the train is going too fast it will reach the intermediate train stop before the relay times out and will be tripped. Before the LS indication is given the preceding train must clear the next signal. A following train train trying to enter a platform before this would have to pass a Stop signal (R/R) and would be tripped.
There is no direct measurement of train speed with this system. 



  N959 Junior Train Controller

Large swathes of the UndergrounD in London were converted to speed signalling in the 1950s. Similar set-up with train stops but straight red/green (2-aspect) UK-style signalling.

If there was any similarity between the two systems there would have been some form of inductor that gauged the speed of the approaching train using the train itself, rather than a countdown timer which is prone to mechanical failure. The approach speed was determined as a 'rolling overlap' between the approaching and departing trains.

I have seen small snippets of bookwirings from the UndergrounD with the general principles laid out - the only real change would be at the concatenation of the aspects at the signal head; the GRs and VCRs are broadly the same in the wiring. Typically, I can't immediately lay my hands on any of the references, although I can remember that Robert Dell (the London Passenger Transport Board's signalling whizz) patented the inductors in the late 1940s

There is more information on LU speed signalling here: http://www.trainweb.org/tubeprune/signalling4.htm and multi-home signalling, although this only really scratches the surface of the installations - the ultimate inspiration for the UndergrounD habits came from either the IND or the BMT in New York and I have seen mention of the Sydney installation too.

There are also locations where there were signal-less train stops controlled by inductors.




"mrfs42"


How fascinating!

Speed measurement by induction. Very simple, in principle.

Too advanced for the 1932 installation at Town Hall and Wynyard, I'd say, and as you mentioned not patented in England until the late 1940s, but still very much worthy of note.

The reference to Sydney you saw may have related to Moorgate Control, which may have been inspired by Sydney's late 1920s system, which was designed under the auspices of an English signal engineer, anyhow.
  awsgc24 Minister for Railways

Location: Sydney
AFAIK, the extremely close headway in the platforms at TH and Wynyard was disabled though not necessarily removed by the 1970s.

"Extremely" means that the entrance signal could clear before the departing train had left the platform.
  N959 Junior Train Controller

AFAIK, the extremely close headway in the platforms at TH and Wynyard was disabled though not necessarily removed by the 1970s.

"Extremely" means that the entrance signal could clear before the departing train had left the platform.
"awsgc24"


Firstly, I'll take that as more confirmation that the system did in fact exist, which is good news.

It would be interesting to know what is still there, even if it is disabled, and why it was disabled.

The "why" may well have gone to the grave with the Signal Engineers involved. Maybe it was cost or cost vs benefit, maybe it was the result of a new risk assessment (or whatever they called them back then), although it sounded pretty safe to me.






  TomBTR Chief Train Controller

Location: near Sydney
Just guessing here - the system was very safe but it did allow the public to see trains moving slowly. Nowadays we are supposed not to notice trains waiting or crawling in the tunnels, just the trains smartly appearing and rolling to a stop at the end of the platform. A small reduction in network capacity but a larger reduction in complaints, perhaps?
  N959 Junior Train Controller

Just guessing here - the system was very safe but it did allow the public to see trains moving slowly. Nowadays we are supposed not to notice trains waiting or crawling in the tunnels, just the trains smartly appearing and rolling to a stop at the end of the platform. A small reduction in network capacity but a larger reduction in complaints, perhaps?
"TomBTR"


I'd like to think that Signal Engineers were immune to that sort of logic. Sounds more like something the dopey Traffic management would come up with.
  awsgc24 Minister for Railways

Location: Sydney


Firstly, I'll take that as more confirmation that the system did in fact exist, which is good news.

"N959"


IIRC, the special signalling used large shelf "Time Limit Opening Relays" which are different from normal shelf timer relays which might be called "Time Limit Closing Relays". The TLORs would have been finally pulled out when the City Underground was rewired with "miniature: Q-type relays in about the 1990s.

In addition to the special overlaps entering the platform whilst the previous train hadn't fully departed, the signal preceding that signal that had no overlap, and its circuit had its trainstop qualified by the next track circuit. There are two similar no-overlap signals approaching Platforms 18 and 19 on the USh and CI respectivelyeven after the 1978 resignalling.
  Aurora8 Assistant Commissioner

Location: Sydney
Rather than further derail the linked thread on SWRL Construction Progress further, thought I'd bring it in here...

'Low Speed', at least in the City Underground, allows a train to proceed at a very low speed, as proved by delayed release of intermediate automatic train stops, as far as the next 'stop' signal. Based only on observation, underground platforms have about 4 ATS along their length, and I am guessing these are 'dropped' in turn as a departing train leaves the platform, allowing a following train, having being given a 'low speed' signal prior to the entrance to the platform, to advance into the platform even as the last carriages of the train in advance are leaving it.
"normw"


Now I've never seen what's been described above occur. I've seen countless times the first train standing beside the platform loading/unloading passengers with a second train waiting behind the previous signal but by the time the second train has proceeded past that signal and reached the arrival end of the platform, the first train is fully in the tunnel at the departure end and on its way to the next station.

Just how common is the quoted scenario to occur in regular working?

Two other signal indications used to exist, namely 'Calling On' and 'Close Up', but if either (or both) still exist and require signalman intervention I can't say.
"normw"


As for Calling On and Close Up, they're still mentioned in the rules, so I'd hazard a guess they'd have to be around somewhere (even if they're not as prevalent as they may have been in past) like, for example, upper quadrant semaphore signals?

EDIT: 3rd time lucky! [I]And size formatting doesn't seem to be working as intended...[/I]
  seb2351 Chief Commissioner

Location: Sydney
Rather than further derail the linked thread on SWRL Construction Progress further, thought I'd bring it in here...



Now I've never seen what's been described above occur. I've seen countless times the first train standing beside the platform loading/unloading passengers with a second train waiting behind the previous signal but by the time the second train has proceeded past that signal and reached the arrival end of the platform, the first train is fully in the tunnel at the departure end and on its way to the next station.

Just how common is the quoted scenario to occur in regular working?



As for Calling On and Close Up, they're still mentioned in the rules, so I'd hazard a guess they'd have to be around somewhere (even if they're not as prevalent as they may have been in past) like, for example, upper quadrant semaphore signals?

EDIT: 3rd time lucky! And size formatting doesn't seem to be working as intended...
Aurora8

I hope calling on signals still exist...Subsidiary shunt on a home signal ring a bell Smile

Calling on, used for a shunt movement where the block ahead may be occupied but the route is set and locked.

As for Close Up, I dont think there is anywhere left in the Sydney area that still uses them, they would be all low speeds technically now.
  Aurora8 Assistant Commissioner

Location: Sydney
I hope calling on signals still exist...Subsidiary shunt on a home signal ring a bell Smile

Calling on, used for a shunt movement where the block ahead may be occupied but the route is set and locked.

As for Close Up, I dont think there is anywhere left in the Sydney area that still uses them, they would be all low speeds technically now.
"seb2351"

Thank you :embarrassed: . I was thinking of something else like a Close Up.
  HeadShunt Chief Train Controller

True calling-on signals are usually marked as such either on the signal itself (e.g. "C" or "CO") or the controlling lever in the signal box. They still exist, but their numbers are dwindling. The majority of surviving true calling-on signals remaining in Sydney are in the areas controlled by Sydney and Strathfield Signal Boxes. Most take the form of a stencil 'CO' beneath double light colour light signals and are not controlled by track circuit, although some have been converted to subsidiary yellow lights while still functioning in the same manner. Other areas have subsidiary yellow lights which are not marked calling-on and in most cases are controlled by a replacement track circuit (the first track circuit in advance of the signal, often the xxxAT). Aside from those differences, it is essentially just a change of terminology from the semaphore era "calling-on" to a more generic "subsidiary" or "shunting" (although "subsidiary" could also be used in reference to miniature semaphore arms beneath home and starting signals, it was not specific).

There are few close-up signals remaining. Another old idea, they are the track circuited equivalent of the Warning (W) signal in the UK used for the Section Clear but Station or Junction Blocked regulation, in modern terms performing the same function as a reduced overlap caution (delayed yellow), without speed control by train stops as provided with the low speed indication. Some have been converted to delayed caution. Broadmeadow, Woodville Jctn, Hamilton Jctn and Newcastle each have at least one.

In summary, there are at least three types of power signals in NSW for reduced overlap working, namely:


  • the approach controlled or conditionally clearing Caution - predates Low Speed, used between Central and Museum in the early days of the Underground, derived from the practice of manually checking trains at semaphore home signals when the starting signal was at danger; reborn as a modern standard, particularly in SSI and microprocessor interlockings.

  • Close Up - banner or subsidiary green marked "CLOSE UP" - derived from absolute block practice - no approach control - few remaining

  • Low Speed - subsidiary green light, no approach control but speed control by train stops at and between signals in train stop equipped areas, prolific in Sydney and Strathfield areas, sparsely scattered elsewhere in network, formerly had special application at Town Hall and Wynyard.


At some locations, subsidiary yellows have also been used as de facto reduced overlap signals, with the train stop lowering either immediately or after occupation of the berth track circuit for a predetermined period, when the line is clear to the next signal but the normal caution overlap is not available. The train stop will not lower if the section is occupied, where the signal effectively functions as a calling-on. However, there is no provision for the subsidiary yellow to indicate "line clear to next signal". Therefore, drivers must technically still be prepared to stop short of any obstruction, even when the train stop is seen to lower on their approach. In most cases these signals have to be selected deliberately by signallers using a different lever or button to that which controls the running signal.

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