Fasts and Slows - any layout preferences?

[eMeS]

Four track working. I'm not a railway engineer, as my query will probably indicate.

In the Milton Keynes area on the WCML, both Fast lines are to the west of the Slow lines. On some other lines, e.g. the ECML at Sandy, I think the Fast lines run between the Slows. Are there any advantages to these different usages? Have usages changed over the years?

 

[yorkie]

See Quadruple Line Track Layouts

Views will vary, but in my opinion, if money was no object, it would be paired by direction (with all lines bi-directional) with flyovers provided at appropriate locations. The southern part of ECML and the South West Main Lines out of Waterloo are mostly like this.

 

[eMeS]

Many thanks for the link - very useful. As I suspected, the reasons are complex.

 

[LowLevel]

It depends really - the problem with paired by use is that it can be difficult and inefficient to cross from fast to slow and vice versa. A point on the network where it often seems to go to pot is Slade Lane/Longsight where you switch between the two systems often leaving stuff standing while it sorts itself out having arrived from or headed for Piccadilly (trains to/from the up/down Oxford Road lines being the main culprits).

 

[swt_passenger]

See Quadruple Line Track Layouts

Views will vary e.g.:

Originally Posted by Bald Rick
The ideal is paired by use, with a nice big gap between the two pairs, and the middle two lines bi-di. Offers best day to day flexibility and the ability to take a pair out for decent engineering work. This is exactly what the Trent Valley is from Nuneaton to Colwich.

In my opinion, if money was no object, it would be paired by direction (with all lines bi-directional) with flyovers provided at appropriate locations. The southern part of ECML and the South West Main Lines out of Waterloo are mostly like this.

The problem here though Yorkie, by quoting Bald Rick's 'ideal' above is that a couple of posts later on in that thread he agrees that he actually meant to write 'paired by direction'!

 

[Asriel]

Swings and roundabouts.

From an operational point of view its probably better to have then grouped by direction as it makes it easier for trains to pass from fasts to slows without blocking the lines going in the other direction.

From an engineering works perspective I think it works better having the fasts on one side and the slows on the other. If the Fasts on the ECML (inside lines) are closed under a possession with the Slows open to traffic its quite difficult to get across the slows to do any work in the middle and more hazardous for the workers with trains running on either side.

 

[asylumxl]

I think paired by use with grade separated junctions is the best possible layout. While this requires more ground work and a higher initial cost, I feel that it makes maintenance of the lines much easier and probably saves money in the long run.

 

[ushawk]

UF-DF-US-DS

A layout like the above would be preferable, whilst one set of lines can be closed for works, a service can still operate on the other lines.

 

[The Planner]

I'm with Bald Rick, the Trent Valley has it right.

 

[edwin_m]

Paired by use (up-down-up-down) is better operationally where the slow and fast lines carry separate services which don't interact very much. This was true of the Midland for example when it was built (the slow lines were mostly goods lines and didn't even have platforms at many stations) but much less true today when Thameslink crosses over several times per hour, conflicting with the opposite-direction track in between. Paired by use is also better at termini because each pair of tracks can lead to its own group of platforms, and termini of paired-by-use (up-up-down-down) main lines often have flyovers so that the last section is paired by direction (Kings Cross, Waterloo, Liverpool Street).

Paired by direction is better at handling a mix of different train speeds, because one can switch between fast and slow without affecting the trains in the opposite direction. However, at places where slow trains terminate or diverge from the main line they have to cross both fast lines - the Welwyn and the new Hitchin flyovers avoid these type of conflicts.

Probably if a line was being quadrupled today it would be paired by direction like the Trent Valley, unless an extension of an existing paired-by-use section. The Trent Valley has bi-di signalling on the central fast tracks so that a service can still run with either the eastern or the western pair closed for engineering work.

The line out of Manchester Piccadilly is paired by use but changes to paired by direction at a flat junction at Slade Lane after the Styal line has diverged from the slows. Under the WCML modernisation this was proposed to be converted to paired-by-use throughout, because this was thought to reduce junction conflicts.

 

[Joseph_Locke]

Paired by use (up-down-up-down) is better operationally where the slow and fast lines carry separate services which don't interact very much. This was true of the Midland for example when it was built (the slow lines were mostly goods lines and didn't even have platforms at many stations) but much less true today when Thameslink crosses over several times per hour, conflicting with the opposite-direction track in between. Paired by use is also better at termini because each pair of tracks can lead to its own group of platforms, and termini of paired-by-use (up-up-down-down) main lines often have flyovers so that the last section is paired by direction (Kings Cross, Waterloo, Liverpool Street).

Paired by direction is better at handling a mix of different train speeds, because one can switch between fast and slow without affecting the trains in the opposite direction. However, at places where slow trains terminate or diverge from the main line they have to cross both fast lines - the Welwyn and the new Hitchin flyovers avoid these type of conflicts.

Probably if a line was being quadrupled today it would be paired by direction like the Trent Valley, unless an extension of an existing paired-by-use section. The Trent Valley has bi-di signalling on the central fast tracks so that a service can still run with either the eastern or the western pair closed for engineering work.

The line out of Manchester Piccadilly is paired by use but changes to paired by direction at a flat junction at Slade Lane after the Styal line has diverged from the slows. Under the WCML modernisation this was proposed to be converted to paired-by-use throughout, because this was thought to reduce junction conflicts.

This latter is actually a form of paired by destination, which was the aim of the WCRM work; the issue is that the stations to Stockport are all "platforms" on the outside" ...

 

[mr_jrt]

My preference is to have the fasts on the outside with the slows in the centre, a-la the Metropolitan line. That way turnbacks don't require any fancy grade separation, and all local stations just require a single island platform. Fast services would need to slow down to stop anyway, so putting in points to give access to the slows and the platforms is trivial. At fast/slow interchange stations you just switch layouts from a single island platform to a pair of islands. Switching between fast and slow lines is also about as high capacity as you can get.

Downsides are that whilst you have all the advantages listed above, branches obviously require grade separation to cross one of the fast lines. Also, the fast lines will want to be as straight as possible to maximise speed - so there will be more land required to spread them out before and after a station...obviously, this isn't a problem when you have the centre lines as the fast lines, which is why the ECML does it this way I suspect.

 

[MarkyT]

My preference is to have the fasts on the outside with the slows in the centre

Definitely worth considering if one was widening an existing route, adding fast tracks one each side of existing slows allowing relatively conflict-free track switching together with simple stations. With modern express passenger trains able to climb fairly steeply, one of the fasts can be 'flown over' a branch diverging from a flat junction in the middle. Overall its 'horses for courses' which arrangement is best for any particular application and many routes contain sections of each, with good reason.

 

[6Gman]

Definitely worth of considering if one was widening an existing route, adding fast tracks one each side of existing slows allowing relatively conflict-free track switching together with simple stations. With modern express passenger trains able to climb fairly steeply, one of the fasts can be 'flown over' a branch diverging from a flat junction in the middle. Overall its 'horses for courses' which arrangement is best for any particular application and many routes contain sections of each, with good reason.

Quite. The WCML is a good illustration of how different arrangements make sense in different places. Crewe-Stafford is by function reflecting freights coming in/out of Basford Hall; Trent Valley is by direction; south of Hanslope is by function again since most of the slower trains run via Northampton.

Horses for courses.

 

[Senex]

Paired by use (up-down-up-down) is better operationally where the slow and fast lines carry separate services which don't interact very much. This was true of the Midland for example when it was built (the slow lines were mostly goods lines and didn't even have platforms at many stations) but much less true today when Thameslink crosses over several times per hour, conflicting with the opposite-direction track in between.

The Midland is a particularly interesting case because it ended up with so much four-tracking and because very often the widening was not done all at once by adding to tracks on one side, but by adding first a track on one side, later a track on the other, and then later again converting the pairing by direction to a pairing by use. And because of the nature of the company's principal traffics it made very good sense to have the additional tracks normally as goods lines and to keep ordinary goods traffic clear of passenger traffic and fast goods (both of course using the main lines).

As edwin_m says, the coming of Thameslink changed things dramatically on the London to Bedford section. Instead of putting in some long loops to the slow lines, so that TL could keep to its own pair of tracks, the cheaper alternative of crossing (on the flat, of course) to the fast lines was taken, involving a conflict and all the joys of approach controlled signalling every time it happened. As levels of service both on TL and the Midland main line grew, problems duly emerged. I can think of a number of locations where the BR/MML on-time HST in which I was travelling was routinely slowed from line-speed to 20 to 30 mph whilst a slightly late-running TL was either got out of the way across to the slow or caused a conflicting movement crossing out path.

As for Slade Lane Jn, well, the PicVic scheme had a flyover planned and authorised for that location, and I certainly know that the idea was at least discussed again more much recently. (But this isn't Reading, or Airport Jn, or Crossrail, so it'll never get done.)

 

[southern442]

What is the layout of the Waterloo-Reading mainline on the section between Clapham jn and Barnes? As far as I know it's a wierd one like DF,DS,UF,US or something like that, can anyone confirm or correct this?

 

[swt_passenger]

What is the layout of the Waterloo-Reading mainline on the section between Clapham jn and Barnes? As far as I know it's a wierd one like DF,DS,UF,US or something like that, can anyone confirm or correct this?

That's correct as far as how it is operated in practice, but the line naming in the Sectional Appendix has been left as the more conventional DS DF UF US. It's operated on a day to day basis with the down line roles swapped to reduce the conflicts that would otherwise be caused by what is a RH junction (as seen if looking west) where most of the fast services go via Richmond, and the slower services go via Kew.

Part of the reason they can easily do this is that the 'Down Windsor' is a single line for a short distance through Queenstown Rd, so they don't have any real issues with swapping trains from DS to DF and vice versa, as they have to go through a single track section anyway...

I touched on this later on in the thread about four tracking that was linked to (by Yorkie) earlier on in this thread, one of the options if the Windsor side route between Waterloo and Clapham Junction ever became usable as a full four track railway again was to operate it as 'paired by use' i.e. with DF UF DS US on the four track section all the way from Waterloo and through Clapham Junction, Putney and Barnes. AIUI that idea is pretty much dormant because even if the Eurostar flyover at Nine Elms was removed they'd prefer to allocate the 8 tracks through Vauxhall as 3 Windsor side, 3 main fasts and two main suburban, because it is the main fasts where the capacity is most needed.