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Post by steeevooo on Mar 17, 2017 10:40:32 GMT
This is something that I've noticed a few times on my evening peak commute home recently, and I'd be grateful if anyone could offer an explanation as to why this happens:
I will be on an Eastbound Jubilee train terminating at Stratford, which is followed a minute or two later by one terminating at North Greenwich. However, upon arriving at North Greenwich we are held by the signaller at a red signal (as announced by the driver) until the following train has pulled into the terminating platform. Only once it has fully pulled in are we then allowed to proceed. It cannot be for the case of allowing any passengers on the terminating train to get onto our train, since there is no time allowance for passengers to alight, go up and over the tracks and down onto the through platform - it purely is a case of the terminating train stopping, opening its doors and then our train shutting its doors and departing.
I'd be most grateful for any insight into this that anyone can offer! |
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Deleted
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Post by Deleted on Mar 17, 2017 11:02:01 GMT
A train reversing in the middle platform needs a reservation on 12 points east of the station as part of its safety distance (equivalent of an overlap in conventional signalling). So if the Eastbound train has a fair amount of dwell time the following North Greenwich reverser will have grabbed the points so that the Eastbound train can't leave until the reversing train is berthed. Usually there will be an allowance in the timetable for this.
The situation might possibly be avoided by bringing the reversing train in much slower to avoid it needing such a long safety distance but that would delay any following eastbound trains and increase the journey time. Not by much but it is these trade offs that are important in calculating headways and customer benefit.
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North End
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Post by North End on Mar 17, 2017 12:56:49 GMT
A train reversing in the middle platform needs a reservation on 12 points east of the station as part of its safety distance (equivalent of an overlap in conventional signalling). So if the Eastbound train has a fair amount of dwell time the following North Greenwich reverser will have grabbed the points so that the Eastbound train can't leave until the reversing train is berthed. Usually there will be an allowance in the timetable for this. The situation might possibly be avoided by bringing the reversing train in much slower to avoid it needing such a long safety distance but that would delay any following eastbound trains and increase the journey time. Not by much but it is these trade offs that are important in calculating headways and customer benefit. Does Seltrac have the capability of offering the signaller the choice of a high or low speed approach? As I see it the system is extremely inflexible - as I understand it we have places on the Northern where a low brake rate is applied to every train to protect berths ahead, even if there's no train standing there! Documentation I have seen suggest Oval northbound is one such place. |
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Deleted
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Post by Deleted on Mar 17, 2017 14:17:36 GMT
A train reversing in the middle platform needs a reservation on 12 points east of the station as part of its safety distance (equivalent of an overlap in conventional signalling). So if the Eastbound train has a fair amount of dwell time the following North Greenwich reverser will have grabbed the points so that the Eastbound train can't leave until the reversing train is berthed. Usually there will be an allowance in the timetable for this. The situation might possibly be avoided by bringing the reversing train in much slower to avoid it needing such a long safety distance but that would delay any following eastbound trains and increase the journey time. Not by much but it is these trade offs that are important in calculating headways and customer benefit. Does Seltrac have the capability of offering the signaller the choice of a high or low speed approach? As I see it the system is extremely inflexible - as I understand it we have places on the Northern where a low brake rate is applied to every train to protect berths ahead, even if there's no train standing there! Documentation I have seen suggest Oval northbound is one such place. SelTrac doesn't offer the signaller a choice in the way you describe since it is supposed to be a hands-off system and there shouldn't be any need for intervention in that way. The use of brake rates is generally to address short term problems with adhesion though as you've noted before there are too many brake rate restrictions left in place at the moment. Forcing trains to slow down for berths or locations where there is limited space ahead is generally done within the core system guideway setup. Only where a problem is noticed and a software change isn't available would temporary changes such as a TSR be used. Occasionally a brake rate change will be useful in this but again should be temporary. I'd be surprised if there's a berthing issue at Oval on a plain line stretch of track. If there's any need to bring a train in slower so that it doesn't, for example, grab a busy set of points then this should be in the guideway data. I don't have access to the documents anymore but if you ask the SSDM or signaller next time you're at Highgate they can show you any BR and TSR restrictions applied on the SMC. |
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class411
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Post by class411 on Mar 17, 2017 14:30:34 GMT
I'd be surprised if there's a berthing issue at Oval on a plain line stretch of track. If there's any need to bring a train in slower so that it doesn't, for example, grab a busy set of points then this should be in the guideway data. I don't have access to the documents anymore but if you ask the SSDM or signaller next time you're at Highgate they can show you any BR and TSR restrictions applied on the SMC. Does the normal ABBR ruling apply to ETLA's? |
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Deleted
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Post by Deleted on Mar 17, 2017 14:33:50 GMT
I'd be surprised if there's a berthing issue at Oval on a plain line stretch of track. If there's any need to bring a train in slower so that it doesn't, for example, grab a busy set of points then this should be in the guideway data. I don't have access to the documents anymore but if you ask the SSDM or signaller next time you're at Highgate they can show you any BR and TSR restrictions applied on the SMC. Does the normal ABBR ruling apply to ETLA's? SSDM: Signal Systems Delivery Manager? BR: Brake Rate TSR: Temporary Speed Restriction SMC: System Management Centre |
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rincew1nd
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Post by rincew1nd on Mar 17, 2017 14:40:54 GMT
A train reversing in the middle platform needs a reservation on 12 points east of the station as part of its safety distance (equivalent of an overlap in conventional signalling). So if the Eastbound train has a fair amount of dwell time the following North Greenwich reverser will have grabbed the points so that the Eastbound train can't leave until the reversing train is berthed. Usually there will be an allowance in the timetable for this. For those that don't understand signalling, this means that the points ahead of the through train are set for the terminating train as a safety measure, in case it overshoots the platform. Once it has stopped the points swing across and the through train can then depart. |
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Deleted
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Post by Deleted on Mar 17, 2017 20:15:28 GMT
I'd be surprised if there's a berthing issue at Oval on a plain line stretch of track. If there's any need to bring a train in slower so that it doesn't, for example, grab a busy set of points then this should be in the guideway data. I don't have access to the documents anymore but if you ask the SSDM or signaller next time you're at Highgate they can show you any BR and TSR restrictions applied on the SMC. Does the normal ABBR ruling apply to ETLA's? Noted. I was in a rush but will check for abbreviations next time. |
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rincew1nd
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Post by rincew1nd on Mar 17, 2017 22:40:03 GMT
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Post by banana99 on Mar 18, 2017 2:16:34 GMT
Does the normal ABBR ruling apply to ETLA's? SSDM: Signal Systems Delivery Manager? BR: Brake Rate TSR: Temporary Speed Restriction SMC: System Management Centre Thanks. I do wonder sometimes.... |
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Deleted
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Post by Deleted on Mar 18, 2017 17:36:53 GMT
All correct except for SSDM = Signal Systems Duty Manager |
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