Are Slow Lines Really Fast Lines with a Lower Speed Limit?

[whhistle]

I might have asked this before but can't find anything on it now.

Take the WCML.
You have slow lines, and fast lines.

Could the slow lines be used at the same speeds as the fast lines? Or is the physical track of a lower grade so can't be hammered as much?

 

[Bletchleyite]

is the physical track of a lower grade so can't be hammered as much?

Yes (and more curves, and less cant etc). Considerable cost went into upgrading the WCML fasts to 125, the cost would have been much higher had all 4 lines been done.

 

[Joseph_Locke]

Not sure Bletchelyite's answer is complete: The Slows are generally on a very similar alignment (and in a few cases a better [Leyland] alignment) than the fasts, but because there has never been much of a need to provide faster speeds on them, the track construction and track quality / maintenance levels on th slows have been tailored down to suit 75 or 90 mph. Only where there is a business driver has a higher speed been designed (100mph south of Hanslope) and of course there was no need for this when the suburban MU fleet couldn't actually do 100mph! Re-canting, in some locations, may need the imposition of new standard differentials to cater for freight trains (with a lower limit in cant deficiency) but tht's a few signs on top of some taming and OLE re-registration work.

On the 4-track sections the signals are all parallel, so most of the slow lines are (in some locations alarmingly) overbraked - the only signalling constraints would be AWS positioning, overlap length and signal sighting.

Lastly, with a mix of freight and stopping services the benefits of "high speed" are relatively few, so it's hard to justify any significant interventions. That said, some of it would be very straightforward to do and could be implemented as part of ongoing renewals at a small extra-over cost (mostly of safety paperwork ...)

 

[LNW-GW Joint]

Yes (and more curves, and less cant etc). Considerable cost went into upgrading the WCML fasts to 125, the cost would have been much higher had all 4 lines been done.

While that's true, the 4-track sections have the same standard of signalling so a big chunk of the fast line speed capability is already there on the slows.
Many of the structures were also upgraded for both fast and slow lines.
The recent 75-100mph upgrade between Stafford and Crewe was quite a small project really, with the resignalling virtually all done a decade ago by WCRM.
The TV4 project gave 125mph fast and slow lines between Tamworth and Armitage, and bi-di signalling south to Rugby on the slows as well as the fasts.
It gets more complicated south of Rugby on the slows with frequent station platforms where the track loops out of line, while the fasts are mostly straight.
But the slows remain 75mph for large chunks (eg Northampton-Rugby-Tamworth), with some 100mph on the open stretches south of Northampton.
And I think the slow line OHLE is still the original BR 100mph spec, only the fast lines were renewed with higher-spec contact wire.
There is no TASS/EPS/tilt on the slows either, except on TV4, so 110mph is the current operational limit anyway.

 

[Joseph_Locke]

There is no TASS/EPS/tilt on the slows either, except on TV4, so 110mph is the current operational limit anyway.

If this was QI, the Alan Davies klaxon would be going off ...

If the braking, sighting, OLE, track geometry, clearances, bridges, aerodynamics and platform widths are all OK, there is no reason why the PS can't be 125mph, with no tilt/TASS/EPS requirement, as this is only to try and get higher speeds on curves. This debate will be ongoing as work to clear HS2 conventional compatible trains on NR lines means that speeds for non-tilt stock (e.g. HS2 conventional compatible trains) have to be raised significantly ot achieve HS2's ambitions for journey time.

 

[edwin_m]

On the 4-track sections the signals are all parallel, so most of the slow lines are (in some locations alarmingly) overbraked - the only signalling constraints would be AWS positioning, overlap length and signal sighting.

This is true where the signalling on both sets of lines is 4-aspect, but it's a common configuration particularly on the ECML for the Slow lines to have 3-aspect signalling. The signals are still parallel (necessary to avoid driver confusion) but the available braking distance on the slows in therefore halved. With this setup all the signals on the Slows would need replacing with 4-aspects if they were to be upgraded to the same speed as the Fasts.

 

[MarkyT]

Of course on the Western we never had "Fast" and "Slow", preferring "Main" and "Relief". There are/were other line naming conventions in use on multi track infrastructure, such as "Through" and "Local" on parts of the Southern, "Main" and "Electric" on the GE (although both have been electrified for about half a century now!). Sometimes when paired by use, parallel tracks may be named by where each pair peels off to at some junction further along the line, even though pointwork might actually allow trains from either pair to access either diverging route.

 

[MarkyT]

With this setup all the signals on the Slows would need replacing with 4-aspects if they were to be upgraded to the same speed as the Fasts.

Or indeed to any higher intermediate speed for which the original three aspect spacing was inadequate.

 

[LNW-GW Joint]

This is true where the signalling on both sets of lines is 4-aspect, but it's a common configuration particularly on the ECML for the Slow lines to have 3-aspect signalling. The signals are still parallel (necessary to avoid driver confusion) but the available braking distance on the slows in therefore halved. With this setup all the signals on the Slows would need replacing with 4-aspects if they were to be upgraded to the same speed as the Fasts.

The WCML has been 4-aspect on all lines since the original electrification in the 60s.

 

[MarkyT]

Few lines were built as four track originally. Almost without exception they started out as a single pair and then later a second pair was added either by placing an additional track either side of original pair or building an independent second pair on a new broadly parallel alignment. The second pair, howsover constructed, was provided for growth clearly but primarily for segregation of traffic, usually to get slower stopping passenger or freight traffic out of the way of faster expresses. The second pair, while sometimes able to take a better faster alignment, often didn't need to do this, so to minimise cost sometimes compromises were made weaving round island platforms and bridge piers etc that impose a speed limit. In other cases where the later alignment could achieve a higher speed, that became the express pair with the original pair remaining for the locals.

 

[DarloRich]

Or is the physical track of a lower grade so can't be hammered as much?

Generally - Same rail type, same sleepers, same ballast, same signalling

 

[driver_m]

This is true where the signalling on both sets of lines is 4-aspect, but it's a common configuration particularly on the ECML for the Slow lines to have 3-aspect signalling. The signals are still parallel (necessary to avoid driver confusion) but the available braking distance on the slows in therefore halved. With this setup all the signals on the Slows would need replacing with 4-aspects if they were to be upgraded to the same speed as the Fasts.

You can still have 125mph 3 aspect signalling though, as seen via Hixon on the WCML.

 

[bramling]

This is true where the signalling on both sets of lines is 4-aspect, but it's a common configuration particularly on the ECML for the Slow lines to have 3-aspect signalling. The signals are still parallel (necessary to avoid driver confusion) but the available braking distance on the slows in therefore halved. With this setup all the signals on the Slows would need replacing with 4-aspects if they were to be upgraded to the same speed as the Fasts.

In the case of the ECML there would need to be some realignment in places where the slows curve to avoid bridges and platforms. In some places speed is limited even lower round some of these, for example 55mph through Brookmans Park on an otherwise 75mph slow line.

 

[edwin_m]

You can still have 125mph 3 aspect signalling though, as seen via Hixon on the WCML.

Yes you can, but if the line is busy enough to have four tracks I'd expect it to have four-aspect signalling at least on the fasts. Excluding very short ones such as station approaches, is there any four-track on the national network that has three-aspect on all tracks?

 

[edwin_m]

The WCML has been 4-aspect on all lines since the original electrification in the 60s.

Yes it does, and I think the SWML has too, but many other four-track sections don't. Although the OP mentioned the WCML as an example, it isn't in the thread title and I wouldn't like anyone reading to think the same arrangement applies everywhere.

 

[LNW-GW Joint]

How about Severn Tunnel-Cardiff?
Or the future Bristol TM-Filton 4-track section?
I just don't know, but the WR seemed to get by on 3-aspect for most of its routes.

 

[TheEdge]

While we are on track speeds and seemingly arbitrary names and speeds...

Is 60mph a magic number in the world of track maintenance? I ask this as I learn the East Suffolk Line, where the vast majority of it is 55mph, with no obvious reason why 60, or higher, isn't possible. Or is it crossing infrastructure related?

 

[The Planner]

It isn't just speed related, track category is based on mean tonnage per annum as well, though 61mph is a boundary between Cat 5 and 4 track on low tonnage routes.

 

[Trainfan344]

The East Suffolk line is a world of it's own, I always avoid it wherever possible.

 

[driver_m]

Lime St tunnels are 3 aspect, 4 tracked and the slow is faster than the fast.
Chester has a small bit of 3 aspect 4 track.

 

[Wilts Wanderer]

Really bizarre is the exit from Bristol Temple Meads towards Filton. Most traffic uses the 40mph Filton Relief Lines, whereas the more lightly used 25mph Filton Main Lines become single at Dr Days Junction and converge back into the Reliefs through a single lead crossover at Lawrence Hill. Though not for much longer tho

 

[Sean Emmett]

Lime St tunnels are 3 aspect, 4 tracked and the slow is faster than the fast.

Someone should start a trivia thread - where are the slow lines faster than the fasts?!

Before the latest remodelling the PSR through Reading on the mains was 50, having been reduced from 80 - so lower than the reliefs which were 60. But the mains are now faster again.

I think there a various quirks on the WCML Trent Valley section and on the Southern

Final thought is where has the designation of running lines changed? Weren't the fasts and slows swapped over going south out of East Croydon?

 

[Bald Rick]

While we are on track speeds and seemingly arbitrary names and speeds...

Is 60mph a magic number in the world of track maintenance? I ask this as I learn the East Suffolk Line, where the vast majority of it is 55mph, with no obvious reason why 60, or higher, isn't possible. Or is it crossing infrastructure related?

The 55 on the East Suffolk is all about the level crossings, many of which are ABCL or AOCL+B; the ‘L’ meaning ‘locally monitored’ (ie by the train driver) and the limit for those is 55mph max.

 

[etr221]

Someone should start a trivia thread - where are the slow lines faster than the fasts?!

The other trivia thread topic is where fast trains run on the the slow line(s), and slow trains use the fasts - this was certainly (and still is?) the case on the LSW Windsor line from Waterloo to Barnes

Final thought is where has the designation of running lines changed? Weren't the fasts and slows swapped over going south out of East Croydon?

Yes, to Stoats Nest, as part of the Three Bridges panel box resignalling in the early 1980s, which finally sorted a differentiation based on the pre-grouping legacy, when the LBSC installed two new tracks, not for SE(C)R use (which is wht the Quarry line is separate - the original line for that stretch was SER.

It's not the only case - another that comes to mind is part of the GE line out of Liverpool Street was swapped as part of the electrification back in the 1940s (Ilford flyover is part of this). And there are a fair number of redesignations - a significant one that comes to mind is Midland mainline Kentish Town-Kettering (AIUI), which in steam days was passenger and goods, changed to fast and slow (and goods lines upgraded for passenger use) - to Bedford for the BedPan dieselisation at the end of the 1950s, not sure what happened further north.

 

[Shaw S Hunter]

Before the latest remodelling the PSR through Reading on the mains was 50, having been reduced from 80 - so lower than the reliefs which were 60. But the mains are now faster again.

IIRC this happened when BR realised that passenger demand was such that all passenger trains should call at Reading meaning only freights went through non-stop. The reduced PSR enabled a small reduction in maintenance requirements/cost.

 

[edwin_m]

It's not the only case - another that comes to mind is part of the GE line out of Liverpool Street was swapped as part of the electrification back in the 1940s (Ilford flyover is part of this). And there are a fair number of redesignations - a significant one that comes to mind is Midland mainline Kentish Town-Kettering (AIUI), which in steam days was passenger and goods, changed to fast and slow (and goods lines upgraded for passenger use) - to Bedford for the BedPan dieselisation at the end of the 1950s, not sure what happened further north.

The four-track Erewash Valley from Trent through to Chesterfield had two passenger and two Goods lines as well, and the surviving parts of the Goods lines were only upgraded to passenger standards with the re-signalling ten years or so back. I think this was also true of Leicester to Trent until the Leicester re-signalling of the late 1980s. Part of the reason was that permissive block was allowed on Goods lines but not on passenger lines unless (in some cases) there was no passenger train in section. On a railway with huge amounts of goods traffic it would help to be able to stack several goods trains nose to tail if necessary.

 

[DY444]

Yes you can, but if the line is busy enough to have four tracks I'd expect it to have four-aspect signalling at least on the fasts. Excluding very short ones such as station approaches, is there any four-track on the national network that has three-aspect on all tracks?

It may not be any more (I haven't been to look since electrification work started) but Tilehurst to Didcot was predominantly 3 aspect on all lines.

 

[MarkyT]

It may not be any more (I haven't been to look since electrification work started) but Tilehurst to Didcot was predominantly 3 aspect on all lines.

I think the speed on both Mains and Reliefs was the same 100mph until they upgraded the Mains to 125mph for the HSTs in the 1970s. The HST of course was designed with braking capability to stop from 125mph in the same distance as previous trains could from 100mph, so it was not necessary to move any signals.

Part of the reason was that permissive block was allowed on Goods lines but not on passenger lines unless (in some cases) there was no passenger train in section. On a railway with huge amounts of goods traffic it would help to be able to stack several goods trains nose to tail if necessary.

My father remembers solid nose to tail WW2 traffic on the old Midland Goods Lines. Congestion was so bad that sometimes trains would move forward only a single block section during a shift! As you say permissive working cannot be used routinely for loaded passenger trains, the only exceptions being at platforms where it is necessary for admitting multiple trains for various purposes such as joining portions.

 

[MarkyT]

A section where Fasts and Slows are the "wrong way round" or at least confusing in modern usage is the former LDCR main line between Shortlands and Swanley. Speed is broadly the same on both pairs apart from around Swanley. The south pair are termed the "Fasts", but actually most express trains to and from Kent use the north pair, the "Slows". For a short while in the early 1990s, Eurostars from London used the "Fasts" as far as Bickley Jn where they turned off to join the SER main line towards Tonbridge. Once the first phase of the CTRL opened, joining the Chatham main line at Fawkham Junction, and the new grade separation was completed at Shortlands, Eurostars switched over to using the "Slows" along with the other Medway and Thanet expresses while stopping traffic, freights and Maidstone trains once again had the "Fasts" largely to themselves. Chatham Expresses using the "Slows" avoids a speed sapping weave at Swanley. The lines might be better being retitled as "Chathams" for the north pair, and "Maidstones" for the south pair throughout. Perhaps something like that will happen at a future resignalling.

 

[GW43125]

The other trivia thread topic is where fast trains run on the the slow line(s), and slow trains use the fasts - this was certainly (and still is?) the case on the LSW Windsor line from Waterloo to Barnes

Still happens, down Windsor and Reading services (semi-fast) use the slow lines as this is a parallel move at Barnes to get to Richmond, stoppers go on the fasts so they can get to Hounslow and stay out of the way.

On the way up, fasts do use the fasts, however.