Re-doubling of single track lines or reinstatement of passing loops

[swissrailpassion]

Something like this perhaps:

http://www.townend.me/files/malton.pdf

It is reported that Malton station is to have an Up platform as part of redevelopment and expansion. A footbridge will link the platforms and there will be access to the site of 700 new houses.

 

[61653 HTAFC]

It is reported that Malton station is to have an Up platform as part of redevelopment and expansion. A footbridge will link the platforms and there will be access to the site of 700 new houses.

One issue with the idea of a single long platform at Malton would be the length of trains on the route. It's one thing at Penryn with 2/4-car Sprinters, but Malton sees 6-car 185s and Nova3 sets of a similar length (5 coaches + loco) so any double platform would need to be more than double the length of the longest possible consist. You also can't use SDO in that situation to get away with shorter platforms, as one train will block the other

Penryn-style solutions are the right approach for some places, but it isn't a magic bullet. If i recall correctly the single platform at Malton is a real headache for planners due to the conflict it creates. A Penryn-style solution wouldn't eliminate that problem.

 

[Strathclyder]

A close relative of singling lines is single lead junctions, and these were installed at a number of locations on the Strathclyde network as well. I never quite got the claimed maintenance benefit of them, how two powered points and a diamond crossing were more expensive than four powered points. Plus there's the capacity issue on the now singled connection, making scheduled parallel moves impossible, let alone the safety issues of a single track section without any of the safeguards, tokens or whatever, you get on a full single line. Nor was flank protection possible at the junction any more.

Anyway, these issues were disregarded, and gung-ho for single lead junctions, possibly part of the same scheme. Within short order there were multiple fatal head-on collisions on them, even just in Strathclyde; Bellgrove was one, Newton was another, and possibly a third. There were a series of them down in England as well. Nobody seemed to have done any risk assessment on the additional conflicts introduced, or the loss of traditional safeguards.

Then, getting back to full single lines, we had the Cowden head-on collision as well, on a line which had been singled.

I was humming and hawing over mentioning single-lead junctions and their inherent dangers in my first post in this thread, specifically with Newton in mind (the 31st anniversary of that particular accident is less than a week away in fact), given that the junction (Newton Kirkhill Junction) at the centre of the tragedy had only been in use in single-lead form for about a month. It was also, by far, the most graphic illustration of the 'PEP'-derived classes' structural weaknesses in a substantial collision, but that's off-topic for this particular thread.

 

[E27007]

The Grain branch in Kent , a branch line from the North Kent line at Hoo Junction between Gravesend and Rochester, is a former double-track passenger line downgraded to single-track freight-only many years ago and the line is non-electrified, there is much talk of reinstatement of the passenger service after doubling of the line, if the rumours come true, the passenger service trains would commence at London Victoria

 

[Ex-controller]

An Internet search showed some photos circa 2008-09.

Am I correct that 'dynamic loop' is a use of 'dynamic' as in 'great', and that here it means 'longer than a standard passing loop'?

Yes, that’s part of it. It consists of more than one signal section, meaning that trains can be signalled in at each end simultaneously. With standard passing loops one one train can be signalled in at a time, meaning the train being looped usually needs to enter first then have an extended wait.

 

[dciuk]

Not aware of any other Cornish redoublings, but then I think all of the surviving branch lines have always been single track anyway (not sure about Newquay given its historic freight traffic over the southern section).

The Newquay Branch has gone in the other direction with the removal of the St Dennis passing loop and the reduction of platforms at Newquay from 3 to 1. I am not sure when those changes happened, but it was after the early 1980's

I don't get why Templecombe isn't 2 platforms, instead of the current setup with the double track starting/finishing right outside the west side of the station, as an eastbound train could sit in the station if waiting for one coming the other way, particularly if there are delays. Of course the act of extending the old platform on the south side to the running line over the old trackbed has I suspect knocked out any prospect of Templecombe station being redoubled anytime soon.

When the double track between Yeovil and Templecombe was re-instated Templecombe station had already closed so would not have factored into the location of where the double track section ended. It is probable it ends where there was already a crossover. Presumably there would have been no budget when re-opening the station in the 80's to have included an extension to the double track and with the current timetable a Yeovil/Exeter bound service has to be significantly delayed before it causes a problem at this location.

If there was a budget available to extending double track, I would have thought more could be gained by extending the Tisbury loop into Tisbury station to make that a 2 platform station compulsory purchasing the down platform if required (the last time I travelled that way it did not seam to be being used by whoever now owns it)

 

[Falcon1200]

Dalreoch - Balloch was singled in 1973.

IIRC part of the rationale for that was to use the recovered OLE for the Lanark branch.

 

[steamybrian]

The Grain branch in Kent , a branch line from the North Kent line at Hoo Junction between Gravesend and Rochester, is a former double-track passenger line downgraded to single-track freight-only many years ago and the line is non-electrified, there is much talk of reinstatement of the passenger service after doubling of the line, if the rumours come true, the passenger service trains would commence at London Victoria

The Grain branch was only a single line throughout its life. When the passenger service operated there were passing loops at Cliffe and Sharnal Street. The line from Stoke Junction to Allhallows was double track but was singled before closure in 1961.

 

[Gloster]

An Internet search showed some photos circa 2008-09.

Am I correct that 'dynamic loop' is a use of 'dynamic' as in 'great', and that here it means 'longer than a standard passing loop'?

My understanding (and I am not a signal engineer, just an old-style signalman) is that a dynamic loop is long enough to make it possible for trains to pass without either having to stop or make a significant reduction in speed. Normally, even with short trains in loops long enough for the longest train, by the time the first train is in clear and the route reset for the second train, either the first train will have to slow down or stop and wait until the second train passes, or the second train has already been checked. This is normally the situation even if the signals for the second train are cleared at the perfect last moment (just as the driver puts his hand on the brake to start slowing).

Of course, unless the dynamic loop is so long that you might as well call it a section of double-track, you still only have a narrow window to get it right. However, you do do have a greater distance in which the train can trundle along slowly to use up time without actually stopping.

 

[S&CLER]

On CTC signalled lines in the USA, I read that despatchers, often hundreds of miles from the location of the trains, talk of "making a mallard" when they arrange it so that 2 trains can pass without stopping in a long loop. The term comes from duck shooting and not from the loco Mallard!

 

[LNW-GW Joint]

Ebbw Vale branch partial redoubling is in progress (after the work was paused for several years).

Some changes were made at Dyfi Jn during the work associated with the Cambrian ETCS installation.
The longer platform with mid-platform crossover from the second track is effectively a loop.
Also on the Cambrian, the Welshpool station loop was extended west to Fron to form a 3-mile dynamic loop.

 

[MarkyT]

...a dynamic loop is long enough to make it possible for trains to pass without either having to stop or make a significant reduction in speed.

In a nutshell. At circa 3 miles in length, Axminster is a long station loop really rather than a classic dynamic facility as everything stops there in normal service. The length gives some flexibility clearly so a slightly late arrival in one direction doesn't immediately impact the other so much. The much longer (10 miles) section between Yeovil Jn and Templecombe includes 2 stations and is really just an extended section of double track on a predominantly single line railway. Trains usually pass somewhere around Sherborne I think, which is planned so level crossing road closed time is minimised.

 

[Taunton]

My understanding (and I am not a signal engineer, just an old-style signalman) is that a dynamic loop is long enough to make it possible for trains to pass without either having to stop or make a significant reduction in speed. Normally, even with short trains in loops long enough for the longest train, by the time the first train is in clear and the route reset for the second train, either the first train will have to slow down or stop and wait until the second train passes, or the second train has already been checked. This is normally the situation even if the signals for the second train are cleared at the perfect last moment (just as the driver puts his hand on the brake to start slowing).

Of course, unless the dynamic loop is so long that you might as well call it a section of double-track, you still only have a narrow window to get it right. However, you do do have a greater distance in which the train can trundle along slowly to use up time without actually stopping.

As explained to me on the onetime single lines radiating from Taunton, the traditional "quarter mile clearing" still applies. So you can't let a train in to stop at the starting signal at the end of the loop if there's another train oncoming within the quarter mile ahead. Not only that, but the signalman needs to be out on the platform, multiple times, while all this is happening to get the token exchange done.

You may care to work out* just how many steps there are (and in what sequence) for the signalman, belling Out of Section, tokens back in, tokens out, detach the hoop, attach the hoop, up the steps, down the steps, exchange with drivers, signals Up, signals Down, getting Line Clear, etc. One of the issues in both the Radstock and the Abermule reports is just how much aspects of all this were being handled by poorly educated, poorly paid country youths of the era, who nowadays wouldn't even have got to their last year in school yet.

* : I'm sure we've got some experts here who can do all this spot on.

 

[rower40]

South end of York station (Holgate Junction) changed from 3 tracks to 4.

 

[Revaulx]

On the Wimbledon-West Croydon railway which is now part of Croydon Tramlink, there was a single line near Mitcham that was reinstated as interlaced gauntlet track. I think there was a plan to properly redouble it to improve service frequency, not sure if it ever went ahead though with the TfL budget woes.

Wasn’t it originally singled following a serious land slip in the cutting? If so, major earthworks would be needed to restore the two-track formation; almost certainly not worth it given its short length.

 

[ac6000cw]

On CTC signalled lines in the USA, I read that despatchers, often hundreds of miles from the location of the trains, talk of "making a mallard" when they arrange it so that 2 trains can pass without stopping in a long loop. The term comes from duck shooting and not from the loco Mallard!

Make that thousands e.g. the BNSF Network Operations Centre (housing 100 to 150 dispatchers) in Fort Worth, Texas, is more than 2000 miles away from parts of the BNSF network.

What you describe is commonly called a 'rolling meet', AFAIK.

It's also common in the US for both tracks of a loop ('passing siding' over there) to be signalled for both directions to allow for same-direction overtaking manoeuvres, so you have a triplet of signals at each end - two exit signals (one per loop track) and an entrance signal (from the single line section).

 

[Railsigns]

A close relative of singling lines is single lead junctions, and these were installed at a number of locations on the Strathclyde network as well. I never quite got the claimed maintenance benefit of them, how two powered points and a diamond crossing were more expensive than four powered points.

A common mistake is to assume that single lead junctions were introduced as a cost-saving measure. While acknowledging that they had their disadvantages, they offered several advantages that made them attractive to track engineers.

Replacing a double junction with a single lead junction usually produced a better track alignment on the existing solum, enabling higher speed movements on and off the branch line.

The switches and crossings on a double junction are concentrated into a small space whereas they're spread out on a single lead junction, which enables greater use of standard track components and easier maintenance. Rail creep problems are also much reduced.

Many of the double junctions that were replaced by single lead junctions had a switch diamond rather than a fixed diamond, so the number of controlled point ends (four) stayed the same. Eliminating switch diamonds is beneficial to maintenance and reliability.

The crossover inherent in a single lead junction can give flexibility for turnback movements or bi-directional running, or it may enable the removal of an existing crossover.

 

[Taunton]

We are grateful for your informed comments from the perspective of a track engineer.

May we ask, did the increased risks (and actual fatality rate experienced) ever get into any calculations? I do notice nowadays I don't see any more going in. When did the Ladbroke Grove "flank protection is for wimps" approach get put to one side?

 

[MarkyT]

A common mistake is to assume that single lead junctions were introduced as a cost-saving measure. While acknowledging that they had their disadvantages, they offered several advantages that made them attractive to track engineers. Replacing a double junction with a single lead junction usually produced a better track alignment on the existing solum, enabling higher speed movements on and off the branch line.
The switches and crossings on a double junction are concentrated into a small space whereas they're spread out on a single lead junction, which enables greater use of standard track components and easier maintenance.

Sometimes the width of the alignment might also be a challenge, otherwise, a long double lead junction made from individual turnouts might be possible, achieving similar speed improvements with the same number of S&C units as a single lead.

Many of the double junctions that were replaced by single lead junctions had a switch diamond rather than a fixed diamond, so the number of controlled point ends (four) stayed the same. Eliminating switch diamonds is beneficial to maintenance and reliability.

Dreadful things! In some cases the extra capacity/flexibility of a double junction can justify accepting the speed limitation of providing a fixed diamond. I think the latest rail profile and standard turnout designs allow a slightly higher speed than traditional UK configurations for the same crossing angle geometry.

The crossover inherent in a single lead junction can give flexibility for turnback movements or bi-directional running, or it may enable the removal of an existing crossover.

The same can apply, to a more limited degree, with the crossover in a double lead.

May we ask, did the increased risks (and actual fatality rate experienced) ever get into any calculations? I do notice nowadays I don't see any more going in. When did the Ladbroke Grove "flank protection is for wimps" approach get put to one side?

I suspect the resultant level of very serious junction collisions DID initially surprise the industry. In retrospect, it can be seen that once traffic levels started growing at a time when the UK had no form of widespread technical train protection*, this was an accident waiting to happen.

* Ladbroke Grove and Southall of course occurred on infrastructure that HAD train protection, but some of the particular trains involved were either not equipped, or were not, for varying reasons, using their onboard systems.

Note I don't think the Ladbroke Grove junction layout, at least from a signalling control point of view, consciously eschewed any form of flank protection. The facing turnout ahead of the SN109 might have been directed towards the down relief in the event of an up main movement, but that would have introduced a new merging conflict closer to the signal, so might have actually been considered more dangerous. Maybe when these decisions were being made, there was an assumption that all the rolling stock would be fitted with the GW-ATP system.

 

[30907]

We are grateful for your informed comments from the perspective of a track engineer.

May we ask, did the increased risks (and actual fatality rate experienced) ever get into any calculations? I do notice nowadays I don't see any more going in. When did the Ladbroke Grove "flank protection is for wimps" approach get put to one side?

Can't answer, but the first of the more sophisticated (and space-consuming) versions, a full double junction with no diamond, dates from well before Bellgrove etc. I remember the concept being described by a friend in the late 70s, and in our circle they were nicknamed "N... junctions" as a result.
Hare Park and South Kirkby are two Yorkshire examples, Standish and Bathampton in the SW - and I think there are one or two that have been upgraded from single-lead (and some that still haven't, such as Haughley).

 

[Pinza-C55]

Sunderland station is being rebuilt from its current configuration of one island platform with two tracks to its original configuration of two islands with 4 tracks.

 

[Brush 4]

Good to see all this Reversing Rationalisation in action.

 

[Falcon1200]

and I think there are one or two that have been upgraded from single-lead (and some that still haven't, such as Haughley).

Several have been upgraded from single lead in Scotland, eg Busby Jc, Midcalder Jc and Newton..... but not Bellgrove !

 

[snowball]

Good to see all this Reversing Rationalisation in action.

Irrationalisation?

 

[Taunton]

I suspect the resultant level of very serious junction collisions DID initially surprise the industry. In retrospect, it can be seen that once traffic levels started growing at a time when the UK had no form of widespread technical train protection*, this was an accident waiting to happen.

* Ladbroke Grove and Southall of course occurred on infrastructure that HAD train protection, but some of the particular trains involved were either not equipped, or were not, for varying reasons, using their onboard systems.

Note I don't think the Ladbroke Grove junction layout, at least from a signalling control point of view, consciously eschewed any form of flank protection. The facing turnout ahead of the SN109 might have been directed towards the down relief in the event of an up main movement, but that would have introduced a new merging conflict closer to the signal, so might have actually been considered more dangerous. Maybe when these decisions were being made, there was an assumption that all the rolling stock would be fitted with the GW-ATP system.

I understand your point, but it really shouldn't have surprised the industry that track designers single-lining at various points had thrown away a traditional safeguard. I suspect that the number of accidents previously prevented by flank protection was a figure not available. Rolt, writing in Red for Danger about the Grantham high speed Spad derailment from 1906, Victorian safety standards, described that where a Down train was expected to stop at the station, with all signals against it, plus there was a conflicting Up movement coming across from the Nottingham line, the Down points were "VERY PROPERLY set for the Nottingham line as well" (doubtless interlocked to ensure this), which the train took, avoiding a worse collision. Very much shades of Southall.

The irony that two of the worst head-on collisions of recent memory both took place on the pioneer ATP route, installed but operators could (twice) not be bothered to use it, is only exceeded by it being quite recently track rationalised, where the former layouts would have diverted both the overruns by flank protection over alternative connections.

 

[8A Rail]

In recent years how many sections of single track have been/are being redoubled (or quadrupled!) or passing loops reinstated thereby reversing some of British Rail’s rationalisation of the network?

Some examples spring to mind:
Part of Chester to Wrexham redoubled
Broad Green to Huyton four track
Hope Valley upgrade ongoing
and coming soon a passing loop between Inverness and Muir of Ord

Incorrect as it is the from four chains west of Roby Station (the new Roby Junction) to Huyton Junction that has been re-instated. The remainder of the line to Broadgreen and westwards until pass Bootle Branch Junction remains two lines.

 

[randyrippley]

This was the section Yeovil Junction to Sherborne, singled June 1967, reinstated to double track October 1967, thus making it likely the first double reinstatement. It was only possible in such short order because the previous second track had not yet been taken up.

It was another ten years or more before platform one was made a through platform, so creating an extra looped section. Previously it had been the platform for the Yeovil shuttle, with a headshunt at the western end.

 

[HamworthyGoods]

The Newquay Branch has gone in the other direction with the removal of the St Dennis passing loop and the reduction of platforms at Newquay from 3 to 1. I am not sure when those changes happened, but it was after the early 1980's

End of the Summer 1987 timetable, a result of sectorisation with the line becoming solely the responsibility of Provincial (as opposed to under the Western Region budget). There where a lot of track and signalling works which Intercity Sector wasn’t prepared to contribute money for and Regional Railways didn’t all those assets so the branch was rationalised.

For everyone that says sectorisation was wonderful there were trade-offs and Intercity making a profit was all very well but it starved some marginal routes that had limited Intercity traffic of investment.

 

[randyrippley]

The section between Templecombe and Yeovil Junction wasn't reinstated as double track in the normal way in that the ex Up line remained a reversible line with the ex down line a diverging loop. A fast Exeter service could approach Yeovil Junction at the same time as a terminating Yeovil Stopper. It may have changed with the line improvements but it remained like that until we'll in to the 2000s.

Or in times of chaos I've seen both tracks blocked with westbounds for Exeter, with an Eastbound trapped in platform 2 at the Junction, only resolved by putting one of the Exeters into (bay) platform 1, so allowing a stream of eastbounds through on the up line, followed by the second westbound getting priority over the first into P2 - while the first westbound eventually reversed out of 1, past the points, and was then allowed westbound through 2, several hours late

 

[Davester50]

Blair Atholl to Dalwhinnie was singled in the 1960s and then redoubled in the 1970s.

A good photo on RailScot website with the barren snowy landscape and recently lifted line shown here.