Great Western Coffee Shop

Journey by Journey => TransWilts line => Topic started by: grahame on July 10, 2017, 14:04:31



Title: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 10, 2017, 14:04:31
In another thread ({here} (http://www.firstgreatwestern.info/coffeeshop/index.php?topic=18431.0)) I documented / described the solution adopted an Penryn on the Falmouth branch for increased capacity.   Doubt has been expressed at the robustness of such an arrangement for a line that's got the potential to be disrupted at both ends ... so here (separate thread) is a list of the various things I can think of that could be done to increase capacity.   Not an expert, so some may be silly and my list may not be complete ...

1. Closer crossover to Thingley Junction
2. Faster junction pointwork
3. Intermediate signals
4. Intermediate loop near but not at Melksham
5. Intermediate loop at Melksham
6. Double junction(s) at Thingley and / or Bradford
7. Double junction(s) with sufficient double track to hold a train off main line
8. Holding loops just off the main lines at Thingley and / or Bradford
9. Dynamic loop(s) between River Avon and Melksham, and Melksham and Thingley
10. Redouble from River Avon to Thingley with "Malton" platform at Melksham
11. Redouble from River Avon to Thingley with two platforms at Melksham
12. Redouble the whole line


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: JayMac on July 10, 2017, 14:33:00
13. Redouble whole line with grade separation at Thingley Junction.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: SandTEngineer on July 10, 2017, 14:35:44
Grahame.  What is the issue with the river Avon bridge that would stop double track being restored across it?


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: martyjon on July 10, 2017, 15:08:06
13. Redouble whole line with grade separation at Thingley Junction.


.... and reinstate a single line Bradford North curve, not so sure about grade separation at Thingley though. 


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: Adelante_CCT on July 10, 2017, 15:20:00
14. Four Track, Now!


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 10, 2017, 15:30:15
Grahame.  What is the issue with the river Avon bridge that would stop double track being restored across it?

I stand open to correction, but I think the double track bridge there may have been replaced by a single track one?   Now that you ask, I'm not so sure.   But it's the major engineering element on the line ...


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 10, 2017, 15:39:55
13. Redouble whole line with grade separation at Thingley Junction.


.... and reinstate a single line Bradford North curve, not so sure about grade separation at Thingley though. 

This idea always worries me as we could end up splitting our southbound service between two destinations, both of which are running not quite frequently enough for them to be virtually a turn up and go service.

You could, however (once you've doubled the track to add capacity) restore both the Bradford East - West and the Thingley South - West curve and then save yourself the Bathampton turn back for MetroWest by running  Bristol Temple Meads, stations to Bath - Corsham - Melksham - Bradford-on-Avon - Avoncliff - Freshford - Bath and stations to Bristol Temple Meads.  I expect that would be very popular and would generate far more revenue that just running the Bath terminator to Westbury putting that up to 3 per hour; Trowbridge and Westbury would probably benefit far more from longer trains than more of them.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: SandTEngineer on July 10, 2017, 16:06:13
Grahame.  What is the issue with the river Avon bridge that would stop double track being restored across it?

I stand open to correction, but I think the double track bridge there may have been replaced by a single track one?   Now that you ask, I'm not so sure.   But it's the major engineering element on the line ...

OK.  I have had a look on GOOGLE MAPS and as best I can see the bridge still looks to be double track width with the current single line slued to the middle of it.

On that basis, I would vote for No.10 (the option that is, not the Downing Street one..... ::) :P )


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: LiskeardRich on July 10, 2017, 16:14:50
Cost wise  something like penryn may be a lowest cost option and more easily justifiable?


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: martyjon on July 10, 2017, 16:17:25
13. Redouble whole line with grade separation at Thingley Junction.


.... and reinstate a single line Bradford North curve, not so sure about grade separation at Thingley though. 

This idea always worries me as we could end up splitting our southbound service between two destinations, both of which are running not quite frequently enough for them to be virtually a turn up and go service.

You could, however (once you've doubled the track to add capacity) restore both the Bradford East - West and the Thingley South - West curve and then save yourself the Bathampton turn back for MetroWest by running  Bristol Temple Meads, stations to Bath - Corsham - Melksham - Bradford-on-Avon - Avoncliff - Freshford - Bath and stations to Bristol Temple Meads.  I expect that would be very popular and would generate far more revenue that just running the Bath terminator to Westbury putting that up to 3 per hour; Trowbridge and Westbury would probably benefit far more from longer trains than more of them.


I was thinking more of a re-instated Bradford North curve acting as a diversionary route when Bathampton to Thingley is closed for engineering works or other times when the direct route is unavailable for traffic.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: Bmblbzzz on July 10, 2017, 17:07:31
If you were going to have MetroWest running in a loop like that using a new line at Thingley, why not just send it on a few more miles to Chippenham and reverse there using a third platform (and then the rest of that loop)?


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: stuving on July 10, 2017, 18:11:44
OK.  I have had a look on GOOGLE MAPS and as best I can see the bridge still looks to be double track width with the current single line slued to the middle of it.

Funny. When I ask Google Earth to measure the width of that bridge, it tells me 4.2m - and a train is over 3.2 m wide before clearances. So definitely single track.  By comparison, there's an accommodation track under the line just to the north-east, with parapets 8.2 m apart.

Now, have any other over- or underbridges on that stretch been renewed since singling and without preserving the double-track width?


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: ellendune on July 10, 2017, 18:12:24
Ok so what is a "Malton" platform then?  I have heard of a different platform arrangement at Penmere.  



Title: Re: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 10, 2017, 18:15:26
Ok so what is a "Malton" platform then?  I have heard of a different platform arrangement at Penmere.  

A double track line but a platform on one line only on the "up" line.  Down line trains cross over as they approach the station via a facing crossover, and cross back upon departure through another crossover.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 10, 2017, 18:30:04
Ok so what is a "Malton" platform then?  I have heard of a different platform arrangement at Penmere.  

A double track line but a platform on one line only on the "up" line.  Down line trains cross over as they approach the station via a facing crossover, and cross back upon departure through another crossover.

I should add that the option is to replicate the current Malton, not the old one.   From Wikipedia:

Quote
Though Malton station now has only one platform in use, at its peak, there were two through platforms and an additional bay platform serving (mainly) Whitby local trains. The George Townsend Andrews overall roof was removed in 1989 and replaced by the canopy recovered from the Whitby platform.

One of Malton station's claim to fame was the novel solution adopted to allow passengers to access the second (island) platform, instead of a footbridge or barrow crossing the NER installed a removable section of platform, in the form of a wheeled trolley running on rails set at right-angles to the (single) running line. When a train had to use the platform, the trolley was wheeled back under the up (York) platform; the trolley was interlocked, with the signals giving access to the platform.

After which I should start drawing a parallel to the turning arrangement at Brockenhurst for wheelchairs. Is that still in use?


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: paul7575 on July 10, 2017, 18:54:09
After which I should start drawing a parallel to the turning arrangement at Brockenhurst for wheelchairs. Is that still in use?
Not since the new footbridge and lifts were completed.   There was talk of the swing bridge being sold to a heritage railway somewhere, but last time I was there (quite a while ago) it was still in situ but unused.

Paul


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: John R on July 10, 2017, 22:13:51
Let's assume for a moment that there has to be a sound business case for any enhancement, and that in these days of NR no longer having a credit card, money is limited. So the redouble all (with or without grade separation at Thingley) is unlikely to tick the boxes. Based on the cost of Swindon -Kemble (£45m for 12 miles), a full redoubling (8 miles) would cost at least £30m.

Before we consider what is needed, we need to consider what service provision we are looking at.  I would suggest that an hourly passenger service is the base, with paths available for freight, and preferably some diversionary capability too.

In terms of an hourly passenger service, in theory doubling isn't needed, as the line is only occupied for around 30 minutes in each hour, with at least one freight slot available per hour in alternate directions. (i.e. 3 tph in total on the line).  However, if an hourly service has a short lay over at Swindon (say 15 mins) then they would be timed to pass on the branch between MKM and Thingley.  That would suggest doubling somewhere along that stretch is likely to be an optimal solution.

I'm aware that every additional switch and crossing (S&C) bumps up the cost significantly.  That would suggest a fairly simple loop, but note then that a dynamic loop costs the same as a passing loop in terms of S&C, and gives much more flexibility.  I'd be inclined not to have the station on the loop, for the reasons well documented in terms of increasing the cost.

A 2 mile loop north of MKM would also have enough room to have two sections, thus enabling two trains to run in the same direction and be passed in the opposite direction. This would provide the freight and diversionary capacity.  It would also mean that if the service from Swindon was more than a couple of mins late, the northbound service could continue to Thingley given the relatively short single section, improving the robustness of the service. Having the doubled section north of MKM also means that any delays on the main line due to waiting a train coming off the branch would be limited.

If for any reason the passenger service envisaged a longer layover at Swindon then the position would switch to having a doubled section south of MKM.



Title: Re: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 10, 2017, 22:38:50
Let's assume ...

That's a fantastic set of logic, John R ... all make sense, though there are assumptions which are not actually certainties.  If two trains pass at Trowbridge, they'll next pass near Royal Wootton Bassett,  and then somewhere between Appleford and Culham prior to a decent turn around time at Oxford.

Another issue which complicates the matter is what happens to different speed paths and if and how trains can be sidetracked. At preset, once a train sets off from Westbury it can't be parked up until Swindon.

Your logic is good .. and it's excellent that these things are starting to be looked at.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 13, 2017, 20:37:55
OK.  I have had a look on GOOGLE MAPS and as best I can see the bridge still looks to be double track width with the current single line slued to the middle of it.

Funny. When I ask Google Earth to measure the width of that bridge, it tells me 4.2m - and a train is over 3.2 m wide before clearances. So definitely single track.  By comparison, there's an accommodation track under the line just to the north-east, with parapets 8.2 m apart.

Now, have any other over- or underbridges on that stretch been renewed since singling and without preserving the double-track width?

Surprisngly (not  ;D ) I came over the bridge early this evening ... watching both sided from on the train, I'm pretty sure that I confirmed it's single track.  90th percentile sureness.

The track has been slewed along the way in a number of places, but I think all the other engineering is still double track.  Growth of foliage has narrowed the way and I'm not sure about erosion.  There's a sign (speed limit) under the road bridge from Holt to Staverton ...


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: Rhydgaled on July 14, 2017, 20:33:17
I'm aware that every additional switch and crossing (S&C) bumps up the cost significantly.  That would suggest a fairly simple loop, but note then that a dynamic loop costs the same as a passing loop in terms of S&C, and gives much more flexibility.
Which begs the question; the cost of one point is equal to how much plain line? I guess that's really two questions, one regarding capital cost and one regarding ongoing maintenance. Logically, once a stretch of single line is short enough it becomes cheaper* to double it and remove the double-to-single pointwork at each end, but what is that distance?

*unless there is something expensive like a single-track viaduct on the section in question

If two trains pass at Trowbridge, they'll next pass near Royal Wootton Bassett,  and then somewhere between Appleford and Culham prior to a decent turn around time at Oxford.
I hope electrification to Bristol Temple Meads and Oxford is still delayed and not cancelled outright; in which case I would sugsgest a 387-operated service between Bristol and Oxford (calling at places like Royal Wootton Bassett as well as the obvious ones such as Bath and Swindon) would be a more-sensible idea than a TransWilts diesel running under the wires east of Swindon; but if there are paths for both why not.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: John R on July 14, 2017, 21:44:39
I'm aware that every additional switch and crossing (S&C) bumps up the cost significantly.  That would suggest a fairly simple loop, but note then that a dynamic loop costs the same as a passing loop in terms of S&C, and gives much more flexibility.
Which begs the question; the cost of one point is equal to how much plain line? I guess that's really two questions, one regarding capital cost and one regarding ongoing maintenance. Logically, once a stretch of single line is short enough it becomes cheaper* to double it and remove the double-to-single pointwork at each end, but what is that distance?

*unless there is something expensive like a single-track viaduct on the section in question


If you double the line fully then you still have additional S&C at either end. Either a crossing and a switch or up to three switches if I'm not mistaken (though it could be just the one if the previous S&C is still considered appropriate to move across the main line double track).   I'm discounting the option of a single lead junction as then you still have the two switches and so haven't made the saving you are implying. (And you also have an arrangement that is rather frowned upon these days since the Bellgrove crash in 1989.

Whichever way, there is no saving, and you still have the additional cost of the extra double track.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 15, 2017, 11:47:36
OK.  I have had a look on GOOGLE MAPS and as best I can see the bridge still looks to be double track width with the current single line slued to the middle of it.

Funny. When I ask Google Earth to measure the width of that bridge, it tells me 4.2m - and a train is over 3.2 m wide before clearances. So definitely single track.  By comparison, there's an accommodation track under the line just to the north-east, with parapets 8.2 m apart.

Now, have any other over- or underbridges on that stretch been renewed since singling and without preserving the double-track width?

Surprisngly (not  ;D ) I came over the bridge early this evening ... watching both sided from on the train, I'm pretty sure that I confirmed it's single track.  90th percentile sureness.

Been across it twice today ... once watching out to the north, once to the south.  I'm now sure it's single track.  Haven't a clue as to the cost or disruption of doubling it. Running time from the double line (south of the crossover) near Trowbridge to the double track capable infrastructure north of the bridge was just 100 seconds in each direction; could have been quicker southbound apart from signal check.   Allowing 3 minutes each / cycle time of 6 minutes would give a theoretical capacity of 10 trains each way per hour; I suspect that none of us would expect even a half of that to be required in the next 15 years!

 


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: simonw on July 15, 2017, 15:09:59
The cheapest way to add capacity to the line is to ensure all stations have two platforms, to allow trains to be held to allow passing fast, non-stop, trains priority.

Out of curiosity could TransWilts be modified to include Calne, Devizes, Marlborough and consequently be a TransWilts network and not a line?



Title: Re: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 15, 2017, 16:07:55
Out of curiosity could TransWilts be modified to include Calne, Devizes, Marlborough and consequently be a TransWilts network and not a line?

TransWilts CIC (Community Interest Company) works for public and sustainable travel to, from and within Wiltshire and Swindon - so there's no need to modify any articles of association at that level, but resources are limited so that's the area we can operate in without any suggestion that we're fully operational in any depth across it.

TransWilts CRP (Community Rail Partnership) is the major division of the CIC, with our core route being Swindon to Salisbury, with the section from Swindon to Westbury being a designated service, and the stations at Chippenham and Melksham being included in that designation.

Looking at other existing lines in the county, the main east - west lines at the top (via Chippenham) in the middle (via or near Westbury) and at the bottom (via Salisbury) aren't closely in scope as services. Community Rail (as defined by government agency / Quango) is about "local lines" and these three are not.  Three other CRPs include other stations in the county (in some form) - and that leaves Bedwyn (admirably covered by Bedwyn Trains) and Pewsey not within any CRP / service group. TransWilts will / is involved as appropriate with the other CRPs - already this month we've been active with two of the others; where it's away from Swindon / Chippenham / Melksham / Dilton Marsh / Warminster, we're the junior partner and it would be unusual for us to lead.

With potential new stations on existing lines, we have taken a look at quite a number and can help (and are helping) with sanity checks, business cases, etc;  on our core line, Wilton Parkway and (later perhaps) Royal Wootton Bassett and noted on the agenda.   Away from our core line, and on sections of line where there's no CRP presence, we're rather more advanced in our current knowledge with Corsham that with Devizes Parkway or Porton Parkway, though it should be noted that Corsham base been mentioned for an exceptionally long time and services types through there make it much the most awkward of those three. And, yes, there are other discussions too.    Some have been dismissed in the form they were discussed after a bit of quick arithmetic with folks looking at neighbourhood plans (for example) , others may come up at some point in the future - either through TransWilts or if another CRP service runs though the site, through them.

TransWilts is about all forms of transport - and you can expect to see more bus as well as train activity from the CIC in the not too distant future.  You mention Calne, Devizes and Marlborough and all three of those are on the TransWilts radar and at least being watched - things like the recent demise of the Sunday bus from Marlborough to Pewsey did not escape our attention, nor have the trials and tribulations of buses in the Vale of Pewsey.

Reopening Railway lines for passengers is also within scope - but most of the suggestions that come up don't add up in the form suggested.  As many such suggestions are quickly forgotten (and because people don't like the maths), you'll find the same / similar ones keep cropping up so it sounds like there's a lot more activity than there really is.   The current "best" case on my understanding for a new passenger service in Wiltshire currently is Ludgershall to Andover - but that's a very early comment indeed and "best" should not be read as saying "good".   Others are more difficult cases, but if you were to envisage Calne growing to a population of 40,000, for example, it would then be the largest town in England without a station and a re-instatememt of the line to Chippenham - with replacement of the footpath bridges over the Avon and the A4 - would warrant a look; it would depend (also) on whether the new population worked in the town or elsewhere, but in the hypothetical circumstance you could have a Calne - Stanley Bridge - Chippenham - Corsham - Bath - stations to Bristol service.   But I don't see plans for another 11,000 homes in Calne on the agenda - the current consultation on new homes in Wiltshire calls for only 1,440 in Calne over a 20 year period.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: John R on July 15, 2017, 19:29:32
The cheapest way to add capacity to the line is to ensure all stations have two platforms, to allow trains to be held to allow passing fast, non-stop, trains priority


Not so for the Thingley Jn to Bradford Jn line.  The cost of building a second platform and all the necessary paraphernalia these days (fully accessible footbridge) means that a big increase in capacity can more cost effectively be achieved by doubling a short section away from the station. A two platform station wouldn't permit fast trains to pass either, as presumably the stopping services would be timetabled to pass at the station (or in the vicinity), so both lines are occupied at the same time.  Besides, I don't think there is a need to have fast trains passing slow trains on that stretch of line.  What is needed is at least two sections, so that two trains can head in the same direction at once, rather than the current situation whereby the first train has to exit the section (which is the whole single track section) before a second can enter. This really reduces overall capacity on the line, as "flighting" of trains in the same direction isn't possible.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: simonw on July 15, 2017, 20:22:03
Thank you Graham for your full reply.

It is interesting that the populations of Calne and Devizes have increased significantly in the last 50 years, and will again in the next 20+ years as we slowly address the housing crisis.

With respect to increasing capacity cheaply, most stations have space, or at least had it in past and ensuring all stations have two platforms, would appear to be sensible and enable higher throughput.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 15, 2017, 21:07:35
It is interesting that the populations of Calne and Devizes have increased significantly in the last 50 years, and will again in the next 20+ years as we slowly address the housing crisis.

Still, on population alone each remains rather small; Calne 17,000 in 2011 ... 1,440 residential units in 20 years at 2.3 people per residence  = 20,312 ... compare to Skelmersdale, still no railway at 40,000.  Also note that Calne likely to be more affluent / more people have their own transport, and Skelmemrsdale in - I suspect - a more marginal constituency.   For Devizes, Parkway proposed; rails into the town would require major rebuild.   Biggest growths are Chippenham and Trowbridge;  Melksham feel like that too (over 2000 new homes; population around 32,000 over the 20 year timescale, and benefits from a train service shared with other flows.)

Quote
With respect to increasing capacity cheaply, most stations have space, or at least had it in past and ensuring all stations have two platforms, would appear to be sensible and enable higher throughput.

It's rarely the platform count at an intermediate station   Length of platform is more important; even this evening, 2 off and 14 on including inebriates and toddlers and an extra minute was gone.  Have to get 40 people on and off through a single door - especially on a 158 where the door is narrower than today's 150, and you have a further minute or two ... not easy to forecast which trains will have the slower passengers, so full train length here makes sense.   BUT the platform is still unused for a large proportion of the time ...

The cheapest way to add capacity to the line is to ensure all stations have two platforms, to allow trains to be held to allow passing fast, non-stop, trains priority

Not so for the Thingley Jn to Bradford Jn line.  The cost of building a second platform and all the necessary paraphernalia these days (fully accessible footbridge) means that a big increase in capacity can more cost effectively be achieved by doubling a short section away from the station. A two platform station wouldn't permit fast trains to pass either, as presumably the stopping services would be timetabled to pass at the station (or in the vicinity), so both lines are occupied at the same time.  Besides, I don't think there is a need to have fast trains passing slow trains on that stretch of line.  What is needed is at least two sections, so that two trains can head in the same direction at once, rather than the current situation whereby the first train has to exit the section (which is the whole single track section) before a second can enter. This really reduces overall capacity on the line, as "flighting" of trains in the same direction isn't possible.

Agree on the need for only one platform.

Flighting is in theory an excellent idea, but due to the long stretch over which the whole flights must travel - Westbury to Swindon - worries me because it's prone to fall over spectacularly when it does fall over.   And even on what should be a quiet day (like today) we can get:

Quote
12:16 Chippenham to Westbury due 12:43 will be diverted between Chippenham and Trowbridge.
It will no longer call at Melksham.
It is being delayed between Chippenham and Trowbridge and is now expected to be 7 minutes late.
This is due to a late running freight train.

Loop in the middle but NOT at Melksham Station's platform, and that diversion wouldn't have been necessary.  Third train in 3 days not calling at Melksham, by the way ... which is a pretty poor record on 16 a day.  93.75% I make it, versus a target of 98.5%.

I would also caution that signalling for a loop that allows a passenger train to overtake a freight is highly desirable - again because of the very long gap otherwise (Westbury to Swindon) between places that trains can be sidetracked.

However, all this stuff has move a bit up the agenda to the extent that there's going to be some real experts taking a look for the future.




Title: Re: Increasing throughput of trains - some ways of doing it
Post by: John R on July 15, 2017, 21:34:13

With respect to increasing capacity cheaply, most stations have space, or at least had it in past and ensuring all stations have two platforms, would appear to be sensible and enable higher throughput.

It's not anything like cheap though. Full accessibility these days means it's very expensive, and it doesn't give you any additional increase in capacity on the branch by having a loop there.  As an example, Ilkeston station cost around £10m for two four car platforms and a footbridge.  Low Moor station was a very similar cost. The addition of a second platform at Alvechurch included major work to provide accessible access to both platforms (in that case the passing loop had to be sited at the station).

So unless money is no object, if you can achieve the same aim/throughput at significantly lower cost by siting the loop elsewhere then it is sensible to do so.

As an aside, I'd suggest that it is also marginally more convenient for passengers only having the one platform, as it avoids the potentially long walk (if ramped) or any delay in using two lifts to access the "other" platform.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: Rhydgaled on July 15, 2017, 21:50:45
I'm aware that every additional switch and crossing (S&C) bumps up the cost significantly.  That would suggest a fairly simple loop, but note then that a dynamic loop costs the same as a passing loop in terms of S&C, and gives much more flexibility.
Which begs the question; the cost of one point is equal to how much plain line? I guess that's really two questions, one regarding capital cost and one regarding ongoing maintenance. Logically, once a stretch of single line is short enough it becomes cheaper* to double it and remove the double-to-single pointwork at each end, but what is that distance?

*unless there is something expensive like a single-track viaduct on the section in question


If you double the line fully then you still have additional S&C at either end. Either a crossing and a switch or up to three switches if I'm not mistaken (though it could be just the one if the previous S&C is still considered appropriate to move across the main line double track).   I'm discounting the option of a single lead junction as then you still have the two switches and so haven't made the saving you are implying. (And you also have an arrangement that is rather frowned upon these days since the Bellgrove crash in 1989.

Whichever way, there is no saving, and you still have the additional cost of the extra double track.
Having now had a look at the sectional appendix 'map' for the line through Melksham I see your point; it would indeed need extra pointwork. However, my question was intended to be a general one of the cost of pointwork versus plain line and there are cases (such as Great Malvern to Ledbury, Avonmouth to Clifton Down, Llandrindod to Llanwrtyd and Swindon to Kemble) where double track would indeed reduce the amount of pointwork (the last has of course been redoubled now, I must have downloaded the sectional appendix quite a while ago). The other sections on that list of examples are simply to illustrate where existing track configurations would/could facilitate a reduction in pointwork following doubling, I don't necessarily have any idea whether there is a demand for double track on any of them or whether they it would be possible to do so.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 15, 2017, 23:28:09
Gut feeling ... if you have more than two mile between passing loops, it'll be cheaper to leave them as separate passing loops than turn them into a single dynamic loop - based on very rough pricings of £6 million per mile (a low figure) to double on existing earthworks, and £12 million for a loop (£8 million for Penryn some 8 years ago)

Avonmouth to Clifton Down (and on to Narroways) would make sense, except that there's a rather nasty viaduct which I suspect is single track over the M32.
 
I think there's a single track tunnel between Great Malvern and Ledbury.

Llandrindod to Llanwrtyd ... until Bog Snorkling becomes as popular a spectator sport as the FA cup final, I doubt that traffic to Llanwrtyd would justify a double line.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: ellendune on July 16, 2017, 08:49:30
Avonmouth to Clifton Down (and on to Narroways) would make sense, except that there's a rather nasty viaduct which I suspect is single track over the M32.

I have never travelled the line and I haven't driven down the M32 for a few weeks but unless there has been a major  tectonic shift in Bristol (And I think we would all have heard about it and felt it if there had been) I do not think the Severn Beach line crosses the M32 at any point as both Narroways and Avonmouth are to the West of it.  You couldn't have meant the M5 either as that goes over the line. 


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 16, 2017, 09:12:23
Avonmouth to Clifton Down (and on to Narroways) would make sense, except that there's a rather nasty viaduct which I suspect is single track over the M32.

I have never travelled the line and I haven't driven down the M32 for a few weeks but unless there has been a major  tectonic shift in Bristol (And I think we would all have heard about it and felt it if there had been) I do not think the Severn Beach line crosses the M32 at any point as both Narroways and Avonmouth are to the West of it.  You couldn't have meant the M5 either as that goes over the line. 

My error - the M32 is crossed between Stapleton Road and Montpelier,  but on the mainline "side" of Narrowways junction. Perhaps it's just a tall embankment? to the west of the junction?


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: Bmblbzzz on July 17, 2017, 11:49:33
There is a bridge over Mina Rd immediately west of Narroways Jnctn. It's a long bridge judged from the road, you'd probably call it a short tunnel, but I think most of what's above is trees with only a narrow area that's railway land. Historically there was another line going straight on into Eastville, of course. It might be possible to double the line there but I guess it would need fairly extensive ground preparation. Only guessing though.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: rogerw on July 17, 2017, 20:43:45
Back in the 1960s when I first travelled on it the Avonmouth line was double track throughout with only the line from Hallen Marsh to Severn Beach as single line.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: Bmblbzzz on July 25, 2017, 13:17:38
I was wondering about door locking; does it really need to be done 40 seconds before the train leaves the platform? That mounts up to a lot of stationary and non-boarding time over a journey.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: ChrisB on July 25, 2017, 13:54:33
Up to.....

And no, the train will leave once doors are secure.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: Rhydgaled on July 25, 2017, 14:00:33
I was wondering about door locking; does it really need to be done 40 seconds before the train leaves the platform? That mounts up to a lot of stationary and non-boarding time over a journey.
It depends how long the platform (and the train) is; a long train will take quite a long time to leave a platform. But that's not what you meant of course; you mean do they need to lock the doors 40 seconds before the driver takes off the brakes and applies power? From my observations as a humble passenger I'd suggest that they don't* BUT having 30 seconds to allow for non-ideal circumstances is prudent; it's just I would much rather they scheduled trains to depart at hh:mm:30 in the working timetable. That way, they would get their 30 seconds without needing the posters+announcments warning that the doors may be locked 30 seconds prior to departure, since the time published in the public timetable would be hh:mm:00 and that'd be the time the door-close button is pressed.

* except when it is a slam-door train and passenger's haven't closed the doors behind them, in which case even 40 seconds might not be enough


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: Bmblbzzz on July 25, 2017, 14:23:28
Yes, I did mean "Does the train really need to stand in the platform with its doors locked for 40s before leaving?" I guess I should time it one day to see whether they actually do; "up to" does make a big difference!


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: PhilWakely on July 25, 2017, 16:29:21
Yes, I did mean "Does the train really need to stand in the platform with its doors locked for 40s before leaving?" I guess I should time it one day to see whether they actually do; "up to" does make a big difference!

Yesterday, I watched the despatcher and guard in action. As the clock ticked over to 10:32:30 the despatcher blew her whistle and the guard responded. The doors were then closed. Once closed, the despatcher repeated the whistle and the guard responded; closed his door and indicated to the driver to depart. At 10:33:00 precisely, the 10:33 departure started to move. There did not appear to be too much 'dead' time in that process.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: IndustryInsider on July 25, 2017, 18:44:39
If you want the train's wheels to start moving pretty much bang on the departure time then 30-40 seconds on a HST is about right, that could (and should) be reduced by 10 seconds for 180s (and other non DOO trains including the new IET trains), and could (and should) be reduced by another 10 seconds for anything running DOO.


Title: Re: Increasing throughput of trains - some ways of doing it
Post by: grahame on July 25, 2017, 18:52:37
If you want the train's wheels to start moving pretty much bang on the departure time then 30-40 seconds on a HST is about right, that could (and should) be reduced by 10 seconds for 180s (and other non DOO trains including the new IET trains), and could (and should) be reduced by another 10 seconds for anything running DOO.

Certainly adding another 30 seconds onto each dwell at Melksham this afternoon with the number of mobility restricted people getting on and off the train ... young children and pushchair day.  Total of 56 passenger off and on the round trip that called at 15:39 / 16:37, but ticket number will show less because lots of under 5s.

Personally, I would like the GBTT time to be the time the doors start to close; why does the rail (and the airline) industry quote a time that's operational focussed rather than customer focussed?



This page is printed from the "Coffee Shop" forum at http://gwr.passenger.chat which is provided by a customer of Great Western Railway. Views expressed are those of the individual posters concerned. Visit www.gwr.com for the official Great Western Railway website. Please contact the administrators of this site if you feel that content provided contravenes our posting rules ( see http://railcustomer.info/1761 ). The forum is hosted by Well House Consultants - http://www.wellho.net