Why Are Some Straight Lines So Slow?

[Envoy]

I have just been watching the Don Coffey You Tube video of Class 175 Chester to Manchester via Warrington. On leaving Chester, the line goes for miles virtually straight yet the speed limit is only 75 mph. Surely, with long welded rail trains such as the 175 should be allowed to do 100 mph? Faster trains would entice more people away from cars as well as cut staff costs and you would cover more miles per train but with higher energy costs.

The Newport to Cardiff 4 track line is also almost straight as it crosses the coastal plain. The two fast tracks (mains) have a speed limit of 95 mph whilst the two relief lines have a speed limit of only 60 mph. Why is this so as they are side by side crossing the same landscape, have the same signal gantries and long welded rail? The relief lines between Newport and Severn Tunnel Junction are even slower with a speed limit of only 40 mph although one of these crosses the Bishton flyover.

 

[Welly]

Underlying track foundation might not be deep enough for 100mph running

 

[The exile]

I have just been watching the Don Coffey You Tube video of Class 175 Chester to Manchester via Warrington. On leaving Chester, the line goes for miles virtually straight yet the speed limit is only 75 mph. Surely, with long welded rail trains such as the 175 should be allowed to do 100 mph? Faster trains would entice more people away from cars as well as cut staff costs and you would cover more miles per train but with higher energy costs.

The Newport to Cardiff 4 track line is also almost straight as it crosses the coastal plain. The two fast tracks (mains) have a speed limit of 95 mph whilst the two relief lines have a speed limit of only 60 mph. Why is this so as they are side by side crossing the same landscape, have the same signal gantries and long welded rail? The relief lines between Newport and Severn Tunnel Junction are even slower with a speed limit of only 40 mph although one of these crosses the Bishton flyover.

Presumably the speed restriction on the reliefs is adequate for what they are mostly used for (freight) and there is little to be gained from the expenditure required to maintain them for a higher speed.

 

[zwk500]

Could also be to do with the strength of underline structures and clearances on the dynamic profiles.

 

[snowball]

It has often been mentioned on here that there are over 80 factors that can effect the speed limit on a section - straightness (radius of curvature) is just the most obvious of them.

 

[Meerkat]

Does seem odd though that the mainline in Wales is significantly slower than elsewhere?

 

[zwk500]

Does seem odd though that the mainline in Wales is significantly slower than elsewhere?

95 is a track maintenance category boundary, IIRC. Given the Severn tunnel is limited and most (all?) trains stop at Newport, the benefit of lifting that is limited. The crossing pointwork for Slow/Fast moves and branches etc may also be limiting the speed as it restricts the use of cant.

 

[Llanigraham]

Does seem odd though that the mainline in Wales is significantly slower than elsewhere?

Considering that it crosses an area that for many years was nothing but a huge tidal bog, and is remarkably unstable, it isn't surprising at all. There are roads across the Newport Levels that "float" on the surface and can be seen moving when a heavy tractor and trailer drive along them.

 

[Meerkat]

95 is a track maintenance category boundary, IIRC. Given the Severn tunnel is limited and most (all?) trains stop at Newport, the benefit of lifting that is limited. The crossing pointwork for Slow/Fast moves and branches etc may also be limiting the speed as it restricts the use of cant.

Admittedly I don’t know the acceleration profiles of trains but there seem to be decent straight bits, with relief lines, either side of Newport, and considering the speed ups for other main lines at various points (ie HST introduction, electrification) 95 seems low - it’s not even the max speed of regional trains nowadays.

 

[zwk500]

Admittedly I don’t know the acceleration profiles of trains but there seem to be decent straight bits, with relief lines, either side of Newport, and considering the speed ups for other main lines at various points (ie HST introduction, electrification) 95 seems low - it’s not even the max speed of regional trains nowadays.

It might seem low, but Newport, Cardiff and Swansea between them are only just over 1 million people. Also on the South Wales ML there are important freight flows to LLanwern and Port Talbot steelworks, that have an impact on junction layouts and so on. There is also the question of whether the formation and underlying geology pose any hazards, etc.
For context, the GWML west of Bristol and Westbury does not exceed 100mph (except for some very brief sections around Highbridge), and the Crosscountry route between Birmingham and Bristol/Cardiff also doesn't exceed 100mph.

95mph is 150kph, and that is higher than many comparable continental lines.

 

[Annetts key]

… and the Crosscountry route between Birmingham and Bristol/Cardiff also doesn't exceed 100mph.

IIRC, some work was done (investigation rather than renewals or heavy engineering work) some years ago, with the aim of increasing where possible some of the (then) speed limits between Yate and the (then) Western Route boundary (it may have gone further).

Some speed limits were increased, as there were amendments in the sectional appendix. But I don’t think there were any radical changes.

As said above, there are many factors behind a line having a particular speed limit. That includes a compromise over signal spacing. A line with a greater distance between signals has a potential for a higher line speed, but at the expense of reduced line capacity. And it’s an expensive business changing the signalling, let alone the track formation.

 

[LNW-GW Joint]

The Chester-Warrington route is handicapped by several metal bridges of doubtful quality, over the Gowy and Weaver and their tributaries.
You can feel the rise and fall over each span over the Gowy, where the ground is also marshy.
There's also the awkward junction at Helsby which (from Warrington) is a right hand junction in the middle of a left hand curve, leading to 40mph towards Chester and 20mph towards Hooton - particularly noticeable on Northern services to/from Chester which do not call. Helsby also still has semaphore signalling on all lines.
Not to mention the CLC junction at Mickle Trafford and the severe approach control at Chester East Jn.
Drivers also use the stretch past Mickle Trafford box for a running brake test.
At Acton Grange there's the choice of upper or lower routes into Bank Quay (WBQ) from the south, where P4, mainly used by Chester trains, is also heavily approach-controlled.
On the lower route via Walton Old Jn, the final crossover to the WCML is only 10mph.
I think the 75mph PSR is the legacy of LMS operation, and nobody has spent any money since to change it.
The fastest bit is the downhill stretch from Runcorn East over the WCML towards Acton Grange, which is quite an efficient 50mph crossover, only to be held at walking pace on the approach to WBQ P4.

 

[The Planner]

IIRC, some work was done (investigation rather than renewals or heavy engineering work) some years ago, with the aim of increasing where possible some of the (then) speed limits between Yate and the (then) Western Route boundary (it may have gone further).

Some speed limits were increased, as there were amendments in the sectional appendix. But I don’t think there were any radical changes.

As said above, there are many factors behind a line having a particular speed limit. That includes a compromise over signal spacing. A line with a greater distance between signals has a potential for a higher line speed, but at the expense of reduced line capacity. And it’s an expensive business changing the signalling, let alone the track formation.

It was altered in several places all the way past Cheltenham. The level crossing changes etc stopped it being fully fulfilled.

 

[D365]

Could also be to do with the strength of underline structures and clearances on the dynamic profiles.

That's the simple answer.

 

[Nicholas Lewis]

I have just been watching the Don Coffey You Tube video of Class 175 Chester to Manchester via Warrington. On leaving Chester, the line goes for miles virtually straight yet the speed limit is only 75 mph. Surely, with long welded rail trains such as the 175 should be allowed to do 100 mph? Faster trains would entice more people away from cars as well as cut staff costs and you would cover more miles per train but with higher energy costs.

The Newport to Cardiff 4 track line is also almost straight as it crosses the coastal plain. The two fast tracks (mains) have a speed limit of 95 mph whilst the two relief lines have a speed limit of only 60 mph. Why is this so as they are side by side crossing the same landscape, have the same signal gantries and long welded rail? The relief lines between Newport and Severn Tunnel Junction are even slower with a speed limit of only 40 mph although one of these crosses the Bishton flyover.

As its above 60mph its in track category 2 which is good for 90mph subject to any geometry, structures, earthworks and clearance constraints. I see it has some semaphore signalling still so its probably historically restricted to 75mph and to move it to a higher speed would need Network Change and a shed load of work to validate signal sighting, clearances, dynamic loading on old bridges first let alone costs for any improvements necessary. This will cost and in todays environment the operator aint going to get funding for that albeit to my mind simple speed improvement schemes should be pursued.

 

[Halish Railway]

This picture is taken from Waterbeach, looking towards Cambridge North - The line is very straight, but the linespeed is a mere 75mph. Once you get going it becomes apparent why its only 75mph - The ride quality is very choppy.

 

[CW2]

The signalling can be an important factor in determining the linespeed. Routes which are still reliant on semaphore signals probably haven't seen much investment in signalling technology in the last 50 years. So as train maximum speeds have increased, if there hasn't been serious investment in the signalling then maximum speed and route capacity will be capped.

 

[Brissle Girl]

The difference between 95 and 100 is only 2 seconds per mile, so by the time you’ve accelerated up to 95 and the when you need to start braking for the approach to Newport you might save 12 seconds, over sticking at 95. Whilst the more fleet of foot electrics might give you a couple of extra miles running at 100, it’s probably never been deemed enough of a benefit to make whatever changes are required. In general, easing areas of low speed offer much more benefit - in that area I’ve often wondered whether an increase in the turnout onto the Ebbw Vale branch (which I believe is still 15mph) is on someone’s enhancement list.

 

[jdp30]

This picture is taken from Waterbeach, looking towards Cambridge North - The line is very straight, but the linespeed is a mere 75mph. Once you get going it becomes apparent why its only 75mph - The ride quality is very choppy.

View attachment 130206

Is the rail really that wobbly or is it just the camera doing that?

 

[dk1]

This picture is taken from Waterbeach, looking towards Cambridge North - The line is very straight, but the linespeed is a mere 75mph. Once you get going it becomes apparent why its only 75mph - The ride quality is very choppy.

View attachment 130206

The short (3 signal sections) 90mph spurt on the down from Bannolds AHB to just short of Dimmocks Cote AHB has always seemed odd to me.

 

[InkyScrolls]

Is the rail really that wobbly or is it just the camera doing that?

It's a bit of both. The sometimes alarming appearance of uneven, but safe track can be exaggerated considerably by perspective. Next time you get chance, stand on a platform end and look down a stretch of straight track - it looks much rougher than it is.

 

[dk1]

It's a bit of both. The sometimes alarming appearance of uneven, but safe track can be exaggerated considerably by perspective. Next time you get chance, stand on a platform end and look down a stretch of straight track - it looks much rougher than it is.

You see that a lot on certain groups. There’s always the old BR stalwarts who say ‘wouldn’t have been like that in my day’ who take great umbrage when you try to tell them it’s the zoom on the lens not the track itself.

 

[Sly Old Fox]

IIRC, some work was done (investigation rather than renewals or heavy engineering work) some years ago, with the aim of increasing where possible some of the (then) speed limits between Yate and the (then) Western Route boundary (it may have gone further).

Some speed limits were increased, as there were amendments in the sectional appendix. But I don’t think there were any radical changes.

As said above, there are many factors behind a line having a particular speed limit. That includes a compromise over signal spacing. A line with a greater distance between signals has a potential for a higher line speed, but at the expense of reduced line capacity. And it’s an expensive business changing the signalling, let alone the track formation.

The line speed was raised from 90 to 100 between Charfield and Yate a few years back.

For reference, on the Great Western the line speed is (basically) 90 mains/40 reliefs between Severn Tunnel Jn and Newport, and 95 mains/60 reliefs between Newport and Cardiff. Line speed through Newport itself is 20/30 depending on platform or 40 on relief (non platform) lines.

 

[Envoy]

Many thanks everyone for your interesting answers thus far to my query regarding sped limits. It has been mentioned that the coastal plain between Severn Tunnel Junction and Cardiff is land that has been reclaimed from coastal marshes and that roads are uneven in this area. This still does not explain why the fast lines can be 95 mph whilst the relief lines are only 40 to 60 mph and all tracks have modern signalling with the same spacing. Use of the relief lines for passenger trains is likely to increase when/if new stations are inserted such as Cardiff East Parkway and Tredegar Park (Newport West).

Semaphone signalling has been mentioned as a limiting factor. These signals must be incredibly old and I did notice large sections of the Chester to Warrington route had them in the Don Coffey video. I also note that virtually the entire Marches Line has these old signals and that this route was supposed to have been fitted with modern signals controlled by the new Canton Control Centre - but this got quietly dropped. However, even with these old signals on The Marches, speeds of 90 mph are allowed on many sections.

It seems to me that if a line does not go to London, there is a reluctance to make any investment that would speed up travel in the regions. Even jointed rail still exists on some lines such as the Cambrian Coast, Heart of Wales and South Pembrokeshire. So, probably the same tracks from the days of steam!

 

[Magdalia]

This picture is taken from Waterbeach, looking towards Cambridge North - The line is very straight, but the linespeed is a mere 75mph. Once you get going it becomes apparent why its only 75mph - The ride quality is very choppy.

View attachment 130206

The short (3 signal sections) 90mph spurt on the down from Bannolds AHB to just short of Dimmocks Cote AHB has always seemed odd to me.

Another factor, particularly important in the Fens, is automatic level crossings. Increasing the maximum line speeds usually involves moving the trigger points for these.

 

[Annetts key]

It's a bit of both. The sometimes alarming appearance of uneven, but safe track can be exaggerated considerably by perspective. Next time you get chance, stand on a platform end and look down a stretch of straight track - it looks much rougher than it is.

Umm, as someone who has walked along the track rather a lot, I’m not sure I agree with that statement. Especially as just looking at it does not give the whole story. For example, unless you know what you are looking at, a lay person would not notice the signs of sleeper voiding, which does contribute to a poor ride.

The speed of the train also has a significant effect on ride quality.

In an ideal world, a straight level section should be completely straight and level, with no visible minor kinks or dips, and the clean part of the rail head should be consistent along its length. In order to see if a rail is level, you also need to be looking at it from a low angle. Not from the height of a person sat in a cab, or stood up on a platform.

It is true however that cameras do lie, as the image depends on the lens. And a round lens ALWAYS distorts the light and therefore the resulting image. Especially if a zoom lens is used.

It seems to me that if a line does not go to London, there is a reluctance to make any investment that would speed up travel in the regions. Even jointed rail still exists on some lines such as the Cambrian Coast, Heart of Wales and South Pembrokeshire. So, probably the same tracks from the days of steam!

Money, or rather the lack of it, is indeed the main reason. However, there will not be much, if any rail dating from the days of steam on main lines or major secondary/branch lines.

Even on lightly but regularly used freight lines/branches the rails are often not that old. Disused or infrequently used freight lines/branches and sidings, that’s another matter…

 

[The Planner]

You also need to consider if a line speed improvement can actually be utilised effectively. Its all very well saving 2 minutes between A and B if you only end up sitting at B for 2 minutes longer. Someone saves time but its often not the leg that has the most benefit.

 

[Dr Day]

This still does not explain why the fast lines can be 95 mph whilst the relief lines are only 40 to 60 mph and all tracks have modern signalling with the same spacing. Use of the relief lines for passenger trains is likely to increase when/if new stations are inserted such as Cardiff East Parkway and Tredegar Park (Newport West).

AFAIK the reliefs don't get used by any passenger trains in normal service, so spending scarce money upgrading them would be of limited value to the railway as a whole and either way completely irrelevant which side of the border they sit. I would presume if the relief lines are to get more passenger use then the cost of upgrading them would form part of the business case for those extra services, if indeed it made much of a difference to the journey time if trains were stopping frequently at the many proposed new stations on that stretch.

 

[The Planner]

AFAIK the reliefs don't get used by any passenger trains in normal service, so spending scarce money upgrading them would be of limited value to the railway as a whole and either way completely irrelevant which side of the border they sit. I would presume if the relief lines are to get more passenger use then the cost of upgrading them would form part of the business case for those extra services, if indeed it made much of a difference to the journey time if trains were stopping frequently at the many proposed new stations on that stretch.

Exactly this, when Newport and the area was resignalled, it was looked at but wasn't considered value for money.

 

[Meerkat]

Exactly this, when Newport and the area was resignalled, it was looked at but wasn't considered value for money.

Bit surprised the politicians didn't get involved - "why is Wales' main line slower than everybody elses"