Single Line Operation = Capacity Enhancement

[Searchlight]

Traditionally, British Crossing Stations have the (short) passing loop in the station, neccessarily needing (usually) TWO platforms, plus a footbridge, or subway. This is expensive and inconveinent.

My proposal, is to have TWO loops either end of a single platform, adequate to take the longest passenger train. The loops would be long by British standards, to accomodate the longest trains.

In the USA, single track is the norm, except for the busiest lines. They reckon on 75% capacity of double track, using Centralised Signalling.......We could use ERTMS-2 Cab Signalling. IF needed, the two loops could be linked, to give a by-pass to non-stopping trains, (eg. Freight)

No need for two platforms, footbridge, lifts etc. Thus making it easier to provide more stations. Of course, not ALL stations would need this layout, only sufficient to handle the frequency of traffic.

 

[Harpers Tate]

No need for.......footbridge, lifts etc.

That depends on access requirements from outside the station. For any location where the station is in the middle of the place it serves, it's reasonable to assume that customers will want to enter from either side and half of them will still need to cross the track(s) one way or another.

 

[Trog]

Would the second loop and its signalling not cost about the same as a second platform?

 

[DaleCooper]

Would the second loop and its signalling not cost about the same as a second platform?

...and require more maintenance than a platform.

 

[Carntyne]

Sounds like a solution looking for a problem here.

 

[The Planner]

I am also unsure about what this is trying to achieve? So the idea is one train comes into the station and a train coming from the opposite direction waits in a loop outside? Surely this sort of situation was solved years ago when we did Penryn? I fail to see how having two loops increases capacity, one train is going to have to stop and wait for the second train to finish the station stop and move before it can go? In my eyes it makes it worse?

 

[matchmaker]

You mean like the majority of stations on the West Highland Railway, dating from 1894?

 

[Bald Rick]

In the USA, single track is the norm, except for the busiest lines. They reckon on 75% capacity of double track, using Centralised Signalling.......

Well they reckon wrong. On any given single track section, capacity cannot be more than 50% of a double track section with the same signalling headway.

Capacity on long freight railways across the prairies is a rather different concept to capacity on a predominantly passenger railway with lots of stations and junctions.

 

[Philip Phlopp]

Would the second loop and its signalling not cost about the same as a second platform?

Yes.

It's a solution looking for a problem. Might be worth the OP writing it down and sending it to DfT though, just the sort of stupid idea they like.

I genuinely cannot fathom out why you would want to add so many additional failure points, which is what you do by adding an additional pair of switches to the track layout with catch points at each end, an additional pair of signals and possibly an additional pair of TPWS overspeed sensors.

And my obligatory OLE notes for electrified routes - it will need an additional wire run, an additional pair of tensioners, additional cantilevers to route the wire run, and four additional end terminating insulators.

It also removes a bit of the ability to terminate a service short, as you don't have a platform to detrain passengers onto, you're left waiting for a platform, then need to send the train into one of the loops, then maybe back to the single platform, before you can start a return service.

As I say, so useless, DfT is bound to love it.

We really don't want to be adding in more failure points anywhere, so one big loop rather than two loops is the way forward.

 

[Searchlight]

Yes.

It's a solution looking for a problem. Might be worth the OP writing it down and sending it to DfT though, just the sort of stupid idea they like.

I genuinely cannot fathom out why you would want to add so many additional failure points, which is what you do by adding an additional pair of switches to the track layout with catch points at each end, an additional pair of signals and possibly an additional pair of TPWS overspeed sensors.

And my obligatory OLE notes for electrified routes - it will need an additional wire run, an additional pair of tensioners, additional cantilevers to route the wire run, and four additional end terminating insulators.

It also removes a bit of the ability to terminate a service short, as you don't have a platform to detrain passengers onto, you're left waiting for a platform, then need to send the train into one of the loops, then maybe back to the single platform, before you can start a return service.

As I say, so useless, DfT is bound to love it.

We really don't want to be adding in more failure points anywhere, so one big loop rather than two loops is the way forward.

Thanks for your comments. The idea of the second loop is partly flexibility and partly redundancy, if one point fails for some reason. Most single lines in this country do not have enougth loops, or are in the wrong places. When CTC was introduced in the USA, they found that many double track lines could be singled. 80% of track in USA is single line with long loops.

Large areas of this country have been deprived of ANY railway service at all. We need to find ways and means of building cheaper railway infrastructure........Not all lines need to be double track, and not all stations need to have two platforms and a footbridge and lifts.

 

[Pinza-C55]

Thanks for your comments. The idea of the second loop is partly flexibility and partly redundancy, if one point fails for some reason. Most single lines in this country do not have enougth loops, or are in the wrong places. When CTC was introduced in the USA, they found that many double track lines could be singled. 80% of track in USA is single line with long loops.

Large areas of this country have been deprived of ANY railway service at all. We need to find ways and means of building cheaper railway infrastructure........Not all lines need to be double track, and not all stations need to have two platforms and a footbridge and lifts.

It would be much better to find a more economical way of building stations such as using precast concrete sections like the Southern Railway used to do. Maybe change the rules also so that we don't need fantastically elaborate footbridges.
If you look at the new Stow the footbridge looks largely unnecessary as they could achieved the same with graded ramps down from the road bridge.

 

[Carntyne]

When CTC was introduced in the USA, they found that many double track lines could be singled. 80% of track in USA is single line with long loops.

Large areas of this country have been deprived of ANY railway service at all. We need to find ways and means of building cheaper railway infrastructure........Not all lines need to be double track, and not all stations need to have two platforms and a footbridge and lifts.

I don't think taking away redundancy (singling routes) is the way to go around tackling capacity problems in the UK. We need more double track. The railways are booming and making money.

 

[Cliveblackpool]

The passing loops do not need platforms! Eg Newquay branch - Goonbarrow Junction,St Blazey, and (now removed) St Dennis Junction.

 

[PHILIPE]

The practice now seems to be to install running loops or lengths of double track as has and still is being installed on the Ebbw Vale Line, Merthyr and Aberdare lines to achieve half hourly service. Also, Axminster, I believe. This means that trains can pass in opposite directions on the run. There is no need to have to wait at crossing points especially if the other train is line. Since a revised timetable on the Heart of Wales Line was introduced in May, there are instances of longer waits at stations waiting to cross, It is, in any case, not an easy route to time because of the crossing points.

 

[Philip Phlopp]

It would be much better to find a more economical way of building stations such as using precast concrete sections like the Southern Railway used to do. Maybe change the rules also so that we don't need fantastically elaborate footbridges.
If you look at the new Stow the footbridge looks largely unnecessary as they could achieved the same with graded ramps down from the road bridge.

There's the TATA Steel Europe modular systems already, they're cheap, quick to install and well engineered, but as with so many railway engineering solutions, the purchase cost is a fraction of the overall cost.

If we're adding a loop outside a station, or adding it at a station with a platform alongside, the bulk of the costs are fixed - there's the installation of switches and crossovers, the changes to the signalling system, moving S&T cable runs, moving signals and installing additional signals, adding TPWS equipment and axle counters.

It might even be necessary to move GSM-R mast installations if they've been put in a silly place, though by the time GSM-R started to be installed, we generally had new equipment being sensibly located for future doubling work.

That's all work which will require possessions and a platoon of S&T engineers out and about, multimeters drawn, and that's when we start rapidly adding zeros to the cost.

If you're on an electrified route, adding a loop requires modifications to the OLE - moving masts, changing some of the catenary components and additional wire runs and tensioning arrangement changes.

That's more possessions, OLE engineers and yet more zeros added to the cost.

Dropping a modular platform, shelter, some lighting columns, PIS and help point is a drop in the ocean compared with the track and signalling costs involved.

 

[Holly]

Well they reckon wrong. On any given single track section, capacity cannot be more than 50% of a double track section with the same signalling headway.

Capacity on long freight railways across the prairies is a rather different concept to capacity on a predominantly passenger railway with lots of stations and junctions.

I seem to recall that the section Altrincham to Navigation Road carries more trains now that it is operated as two bidirectional single tracks than it did when it was operated a one double track section. At a cost of greatly increased journey times between Northwich and Manchester.

 

[swt_passenger]

I don't quite understand the equals sign in the thread title.

Does it mean singling is equivalent to capacity enhancement?

 

[jopsuk]

Perhaps this might be useful for reopening projects, certainly has little or no use on existing lines

 

[MarkyT]

What works for a freight railroad in the US may not for an intensive passenger railway in the civilised world . It is possible to install intermediate 'flighting' signals all the way in both directions through a long single line between A & B to allow trains to follow each other closely and you could run intensively in one direction from A to B all day but the big problem is when you want to switch direction. You have to wait for the last train in one direction to completely clear the single line at B before sending the first one in from B to A. Some freight roads in the US use this flighting technique to handle high volumes with (say) a series of northbounds in the mornings, and southbounds in the afternoon. In some trunk corridors there are broadly parallel single lines between major cities via different routes which, although they each remain fully signalled for both directions, are used predominantly in opposing directions over the longer corridor. Minor traffic flows which go in the 'wrong' direction can still be handled on each route but they clearly have to give way to the predominant flow direction, getting 'sidetracked' frequently and waiting a long time when they do.

Loops for passenger operations are best located at stations so any out of course waiting can be done at a platform where passengers can be de-trained or trains reversed, if something goes wrong subsequently. Passengers also notice a wait slightly extended over normal at a station far less than they would an unexpected stop in the middle of nowhere.

For a longer distance mainline type of operation a 'dynamic loop' arranged either side of a station stop like Axminster on the Waterloo - Exeter line works very well. Here the loops are around 3 miles long which gives a little resilience to cope with minor late running, preventing a small arrival delay in one direction impacting departure in the other. The loop turnouts must be designed for fast running in either switch position in this case, to avoid unnecessary slowing so far from the station.

For shorter, more self-contained routes, shorter passing loops with slower, cheaper turnouts closer to the platform ends are more appropriate.

A variant of the short branch line loop is the 'Penryn style' design. Here platforms for both directions are arranged sequentially on the same side of the single line and one of the loop turnouts is situated between them with a bypass line allowing access for one train around another train already standing in one of the platforms. In the UK this was first employed on the Truro-Falmouth branch in Cornwall when services were increased in 2009.

https://en.wikipedia.org/wiki/Penryn_railway_station

A similar arrangement has since been provided at Dovey Junction (Cyffordd Dyfi) on the Cambrian line in Wales. The loop was reinstated in this manner with an extended platform along the Aberystwyth line in conjunction with route capacity work and the pilot ETCS resignallling project.

The big advantage of the 'Penryn-style' layout is the avoidance of a very expensive and perhaps difficult to build and visually obtrusive DDA compliant access footbridge to a second platform remote from the main station street access. Sometimes this is not an issue, for instance when the railway is in a cutting or embankment and compliant access to both platforms can be made from a road bridge via relatively low cost graded footpaths up or down the earthworks. The access consideration (or the cost increment versus a simple stepped footbridge) became necessary once disabled regulations were given the force of law and because pedestrian level crossings for such purposes also became unacceptable for safety reasons in new schemes. Lifts can be used in conjunction with stairs to avoid long ramps, but they are also very expensive and more importantly with branch lines raise many concerns over security, failures and maintenance, power supply robustness, etc , etc. They are completely inappropriate really at unmanned stations.

It is interesting to note by contrast that if a railway is classified 'light rail' then pedestrian level crossings for access from one platform to the other are perfectly acceptable under current regulations and guidance even with high platforms and very frequent service on a largely segregated double track route. For many examples see Manchester Metrolink.

 

[Searchlight]

I don't quite understand the equals sign in the thread title.

Does it mean singling is equivalent to capacity enhancement?

Sorry, No, thats a typo. The enhancement comes with putting in more loops along the line.
--- old post above --- --- new post below ---

What works for a freight railroad in the US may not for an intensive passenger railway in the civilised world . It is possible to install intermediate 'flighting' signals all the way in both directions through a long single line between A & B to allow trains to follow each other closely and you could run intensively in one direction from A to B all day but the big problem is when you want to switch direction. You have to wait for the last train in one direction to completely clear the single line at B before sending the first one in from B to A. Some freight roads in the US use this flighting technique to handle high volumes with (say) a series of northbounds in the mornings, and southbounds in the afternoon. In some trunk corridors there are broadly parallel single lines between major cities via different routes which, although they each remain fully signalled for both directions, are used predominantly in opposing directions over the longer corridor. Minor traffic flows which go in the 'wrong' direction can still be handled on each route but they clearly have to give way to the predominant flow direction, getting 'sidetracked' frequently and waiting a long time when they do.

Loops for passenger operations are best located at stations so any out of course waiting can be done at a platform where passengers can be de-trained or trains reversed, if something goes wrong subsequently. Passengers also notice a wait slightly extended over normal at a station far less than they would an unexpected stop in the middle of nowhere.

For a longer distance mainline type of operation a 'dynamic loop' arranged either side of a station stop like Axminster on the Waterloo - Exeter line works very well. Here the loops are around 3 miles long which gives a little resilience to cope with minor late running, preventing a small arrival delay in one direction impacting departure in the other. The loop turnouts must be designed for fast running in either switch position in this case, to avoid unnecessary slowing so far from the station.

For shorter, more self-contained routes, shorter passing loops with slower, cheaper turnouts closer to the platform ends are more appropriate.

A variant of the short branch line loop is the 'Penryn style' design. Here platforms for both directions are arranged sequentially on the same side of the single line and one of the loop turnouts is situated between them with a bypass line allowing access for one train around another train already standing in one of the platforms. In the UK this was first employed on the Truro-Falmouth branch in Cornwall when services were increased in 2009.

https://en.wikipedia.org/wiki/Penryn_railway_station

A similar arrangement has since been provided at Dovey Junction (Cyffordd Dyfi) on the Cambrian line in Wales. The loop was reinstated in this manner with an extended platform along the Aberystwyth line in conjunction with route capacity work and the pilot ETCS resignallling project.

The big advantage of the 'Penryn-style' layout is the avoidance of a very expensive and perhaps difficult to build and visually obtrusive DDA compliant access footbridge to a second platform remote from the main station street access. Sometimes this is not an issue, for instance when the railway is in a cutting or embankment and compliant access to both platforms can be made from a road bridge via relatively low cost graded footpaths up or down the earthworks. The access consideration (or the cost increment versus a simple stepped footbridge) became necessary once disabled regulations were given the force of law and because pedestrian level crossings for such purposes also became unacceptable for safety reasons in new schemes. Lifts can be used in conjunction with stairs to avoid long ramps, but they are also very expensive and more importantly with branch lines raise many concerns over security, failures and maintenance, power supply robustness, etc , etc. They are completely inappropriate really at unmanned stations.

It is interesting to note by contrast that if a railway is classified 'light rail' then pedestrian level crossings for access from one platform to the other are perfectly acceptable under current regulations and guidance even with high platforms and very frequent service on a largely segregated double track route. For many examples see Manchester Metrolink.

Thanks for this. The Axminster set-up is what I rather had in mind at the top of this thread. The Penrhyn design is obviously suitable for some locations, and does eliminate the 2nd platform. As the double loop is installed at Axminster.......Maybe not such a daft idea after all?:roll:

 

[jopsuk]

Um, I think you misunderstand the Axminster arrangement. It's really just a standard two-track station in the middle of a three-mile section of double track railway.

 

[HSTEd]

Or we could just do a Penryn.

 

[Yabbadabba]

Um, I think you misunderstand the Axminster arrangement. It's really just a standard two-track station in the middle of a three-mile section of double track railway.

Just to back up what you've said.

 

[swt_passenger]

Sorry, No, thats a typo. The enhancement comes with putting in more loops along the line.

You may not realise already, but if you go back and edit the post (in advanced mode) you can fix the title...

 

[edwin_m]

When thinking about single track layouts you need to understand how signalling works, particularly in respect of overlaps. Basically if a train is approaching a red signal there usually needs to be 200m or so of clear track after the signal, as a safety margin in case it fails to stop at the right place. The overlap is released for use by other trains by a timer, which is set so the train in question must have reached the signal and stopped or at least be moving very slowly. For traditional semaphore signalling the rules are a bit different but have a similar consequence.

This means basically that two trains can't enter a passing station simultaneously unless the loop extends for at least 200m either side of the station. It also means that if the two trains were stopping on the same track they would need to be a gap of 200m or more between them! There are some situations where this can be reduced or avoided but they involve running the trains more slowly. I think the Penrhyn arrangement only works if one train arrives before the other one.

 

[DarloRich]

Traditionally, British Crossing Stations have the (short) passing loop in the station, neccessarily needing (usually) TWO platforms, plus a footbridge, or subway. This is expensive and inconveinent.

My proposal, is to have TWO loops either end of a single platform, adequate to take the longest passenger train. The loops would be long by British standards, to accomodate the longest trains.

In the USA, single track is the norm, except for the busiest lines. They reckon on 75% capacity of double track, using Centralised Signalling.......We could use ERTMS-2 Cab Signalling. IF needed, the two loops could be linked, to give a by-pass to non-stopping trains, (eg. Freight)

No need for two platforms, footbridge, lifts etc. Thus making it easier to provide more stations. Of course, not ALL stations would need this layout, only sufficient to handle the frequency of traffic.

"Penryn" loop surely?

 

[snowball]

I seem to recall that the section Altrincham to Navigation Road carries more trains now that it is operated as two bidirectional single tracks than it did when it was operated a one double track section.

I imagine that claim's achieved by counting a tram as a train. The trams are at 6-minute frequency in each direction through most of the day on weekdays, which is certainly more frequent that the trains ever were.

 

[Kentish Paul]

The passing loop outside the station also occurs to the east of Tisbury. The loop (both tracks) are bi-directionable. If a down train is late the up train will leave the station and enter the loop. The down train will then pass on the through track and stop at the platform.

The opposite happens if the up train is late. The down will wait in the loop and proceed to the platform once the up train has cleared.

On my various journeys to Yeovil the latter seems to happen more often.

 

[edwin_m]

I seem to recall that the section Altrincham to Navigation Road carries more trains now that it is operated as two bidirectional single tracks than it did when it was operated a one double track section. At a cost of greatly increased journey times between Northwich and Manchester.

The total of trains plus trams now is far more than the number of trains previously. However that doesn't say anything about the capacity of the route - it is close to maximum capacity now but would have been way below maximum capacity before.

 

[Searchlight]

The passing loop outside the station also occurs to the east of Tisbury. The loop (both tracks) are bi-directionable. If a down train is late the up train will leave the station and enter the loop. The down train will then pass on the through track and stop at the platform.

The opposite happens if the up train is late. The down will wait in the loop and proceed to the platform once the up train has cleared.

On my various journeys to Yeovil the latter seems to happen more often.

Thanks for that........Bi-directional operation of loops is the norm on USA and other countries lines signalled with CTC. Turnback facilities could be provided by putting in a bay platform, attached to the main platform.