Increasing throughput of trains - some ways of doing it

[whole diary]

[paul7575]

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

[John R]

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^» (Network Rail - home page) 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^» (Melksham (Station code) - next trains) 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^▸ (Settle and Carlisle )) 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.

[grahame]

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.

[grahame]

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  ) 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 ...

[Rhydgaled]

I'm aware that every additional switch and crossing (S&C^▸ (Settle and Carlisle )) 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.

[John R]

I'm aware that every additional switch and crossing (S&C^▸ (Settle and Carlisle )) 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.

[grahame]

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  ) 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!

 

[simonw]

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?

[grahame]

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 ) (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) (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.

[John R]

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.

[simonw]

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.

[grahame]

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.)

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:

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.

[John R]

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.

[Rhydgaled]

I'm aware that every additional switch and crossing (S&C^▸ (Settle and Carlisle )) 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.

[grahame]

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.