Welwyn Viaduct Bottleneck

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HSTEd

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Well it seems that with the construction of the Hitchin-to-Cambridge flyover attached to the Thameslink programme is to be taken in hand relatively soon (assuming work hasn't already started), there is only one major bottleneck remaining on the Southern ECML, that being the two track section surrounding the Welwyn Viaduct and its attached tunnels.

As far as I can see this will have to be dealt with sooner or later as it must be putting a damper on the suburban and intercity timetables.

The options as far as I can tell are:

1) Leave as it is and either invest in diverting additional freight and passenger trains via the Hertford loop to free up paths or simply put up with the restriction

2a) Construct a new pair of two-track tunnel bores to quadrouple the line north of Welwyn North station, rebuilding the station completely to allow the four track section to extend all the way to the North end of the bridge, reworking the track at the south end to enable all four tracks to reach the South end, shortening the twin track section by more than half and removing the station from it.

2b) Construct a new viaduct immediately to the east of the current one, probably with strengthening of the original bridge's foundations and placing the new supports so that the original view down the valley is preserved to the greatest possible extent.

3) Construct a twin-track tunnel from the northern end of the Northernmost Welwyn tunnel to somewhere immediately north of Welwyn Garden City station, allowing it to carry the fast tracks under the valley, this is the most expensive option but would completely remove the bottleneck with minimum disruption to the visual environment surrounding the existing Viaduct, it would however have to be rather steeply graded to reduce its length and cost and thus freight trains would be unable to use the fast line during engineering works.

I myself support either option 2a or 2b (if unlimited money was available) however I fear we will get nothing happening whatsoever.
 
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MidnightFlyer

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I doubt it will ever change on account that it is exceptionally expensive to bore tunnels or build viaducts to modern standards. I would have thought, though, that an extra viaduct is the more likely of the two.
 

yorksrob

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2a) Construct a new pair of two-track tunnel bores to quadrouple the line north of Welwyn North station, rebuilding the station completely to allow the four track section to extend all the way to the North end of the bridge, reworking the track at the south end to enable all four tracks to reach the South end, shortening the twin track section by more than half and removing the station from it.
.
I'm guessing you mean single track bores either side of the existing tunnel, in which case I'd have thought it would be easier to build one double track tunnel along side of the existing one and continue this to a new viaduct alongside the existing one.
 

HSTEd

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I'm guessing you mean single track bores either side of the existing tunnel, in which case I'd have thought it would be easier to build one double track tunnel along side of the existing one and continue this to a new viaduct alongside the existing one.
No, I mean a pair of two track tunnels to match the current pair of two track tunnel bores, if for no other reason than there are all those regulations about single bore tunnels.
I didnt use the best language there but you remember there are two tunnels immediately north of the Viaduct.
 

ntg

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What are the prospects of adding a second deck to the viaduct somewhat like having a elevated set of tracks over it...assuming the tunneling issue can be overcome?

I doubt that the construction of a second viaduct would ever be possible due the historical nature of the current viaduct and surround area.
 

yorksrob

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No, I mean a pair of two track tunnels to match the current pair of two track tunnel bores, if for no other reason than there are all those regulations about single bore tunnels.
I didnt use the best language there but you remember there are two tunnels immediately north of the Viaduct.
Oh, I see - you mean a pair in succession. Yeah, I think that would be a good idea, although I doubt there would be much point without continuing and duplicating the viaduct to eliminate the pathing conflicts altogether.

Looking at the number of tunnels on HS1, I don't think these would be too big a deal. The viaduct would be more tricky as you'd presumably need to use traditional building methods and materials that were sympathetic to the original. However, bearing in mind the relatively short length of the section and the importance of it I think it would be well worth the investment.
 

philjo

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I don't think Welwyn will be directly widened.
short term, hitchin flyover allows the timetable to be built around just Welwyn rather than hitchin bottleneck as well. Plus upgrading of Hertford loop.

Longer term HS2 will take some long distance traffic away to give more cpaacity on trains for intermediate ECML stations.
An eastern HS Line (via Stansted) will allow the London-Cambridge traffic to bypass Welwyn so the local services are serving the Hertfordshire/Beds stations.
 

HSTEd

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What are the prospects of adding a second deck to the viaduct somewhat like having a elevated set of tracks over it...assuming the tunneling issue can be overcome?

I doubt that the construction of a second viaduct would ever be possible due the historical nature of the current viaduct and surround area.
If people object to a second viaduct Im not sure how they would like the complete reconstruction of the existing one with a shiny upper deck, in addition I doubt the foundations of the viaduct could take all the extra load without an enormously expensive rebuild.



Otherwise rebuilding the station in combination with those tunnels would mean that the commuter trains at Welwyn North would only be braking on the two track section, and would stand and accelerate again (going Northbound anyway, south would be reversed) on four tracks, which would permit InterCity trains to pass at high speed through the station whether or not there was a commuter train in it.
 
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yorksrob

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There are quite a few (admittedly stumpier) viaducts near London which have been widened over the years so that the join is almost imperceptible. I can't think of any as high or in as picturesque a setting but I'd be surprised if they couldn't do similar here.
 

jopsuk

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The viaduct would be more tricky as you'd presumably need to use traditional building methods and materials that were sympathetic to the original. However, bearing in mind the relatively short length of the section and the importance of it I think it would be well worth the investment.
You could presumably build something using modern materials and methods that's the same shape as the existing viaduct, and basically brick-clad it?
 

yorksrob

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You could presumably build something using modern materials and methods that's the same shape as the existing viaduct, and basically brick-clad it?
I'd have thought so - although the engineering guys would be better placed to confirm. I remember reading that even the Euston Arch was built around a brick and iron frame.
 

HSTEd

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What about just adding loops at the station to allow non-stop services to overtake stopping ones?
You end up with a rather short loop north of the station unless you rebuild the platforms, but it could be done, not sure how much good that does as your trains will still be accelerating quite slowly away from the station on that long two track section.

And then theres the listed station building to consider, which is a more major proposistion for such a minor remodelling.
 

Tomnick

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Loops wouldn't do much - as well as putting a good five minutes into anything stopping at Welwyn North, the stopper's still taking two paths.
 

gazthomas

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Close the station at Welwyn North - it is a bit of an induldgance given WGC is near. Stevenage couldn't justify retaining its old station after all.
 

philjo

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Roger Ford in Modern Railways once suggested extending the down slow line from Digswell over an extended viaduct to terminate in a new platform at Welwyn North. I think one track would be added to the west side of the viaduct.
The line would be bi-di from WGC so some of the moorgate trains would terminate at Welwyn North then reverse back to WGC & over the flyover.
The other trains need not call at Welwyn North (may be hourly off-peak) as can change at WGC.

This option would not require any tunnelling works.

Closing the station completely would not be popular - I believe that Welwyn north has one of the highest proportion of first class season ticket holders than other GN stations - most of whom would probably prefer to drive into London instead of driving into WGC to catch a train.
Many people also drive from the surrounding area to get the train from Welwyn north.
 

jon0844

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The people at Welwyn North must like driving, as they totally block all the surrounding roads (or used to - I think there are restrictions there now). They may have their FC tickets paid for, but they wouldn't pay to park in the station car park!

If Hadley Wood had more trains stopping that had first class, I bet FCC would make a fair bit there too.
 

Lee_Again

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Given that any solution involving the viaduct would cost 'lots', my ideas would involve a few smaller projects that, in my imaginary world, would cost less and produce similar results.

1) upgrade the section between Bell Isle (where the new TL junction will be) and Finsbury Park to 6 tracks. That would involve bringing back in to use the two existing tunnels directly outside Kings Cross and rebuilding the flyover and other works.
This would allow the TL service to be grade seperated from the ECML.

2) upgrade Finsbury Park to Alexandra Palace to six tracks. This is largely being done already. Again, keeps TL traffic of the mains.
Another benefit of 1 and 2 is that delays on the TL (see recent posts) will not spill over on to the ECML.

3) upgrade Hertford Loop to 100mph and put passing loops in at Godon Hill. The timetable could be done so that the stoppers pull in to the loop as the fasts pass. 4 stoppers per hour and 4 fast per hour.
I think this would cause a 6 minute extension to the Kings Cross > Cambridge fasts.

4) Give the Open Access guys a path each hour (a proper fast past all the way to Doncaster) but insist they run together as far as Doncaster. Here they would split and go their seperate ways. Splitting could be done in the yard if platform space at Doncaster is an issue. HST's to Sunderland?? Make the Open Access guys use the same trains (or at least compatible for multiple working).

5) Add a 5th line between Langley and Hitchin in the Down direction. This would allow the fasts from Hertford to continue up to the flyover without passing across the slow on to the fast. It would combine with the existing down slow just south of Hitchin station. Probably best to put a bay in at Stevenage for the stoppers (between existing down slow and my new down 5th track).

6) not sure about this - 2 per hour off Hertford and 2 per hour from Welwyn run through Cannonbury tunnel (should cope with 8tph on the single bore - but little ECS movements allowed) on to the NLL and join the Overground services to South East London etc. The 313's need replacing soon(ish) and those new trains would be perfect with a few more seats.

Thoughts
 

philjo

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Once Hitchin flyover is in use more of the Hertford services that terminate at Stevenage can run though & terminate at Letchworth GC without impacting the fast lines. At the moment they block platform 4 at Stevenage. This will also give Letchworth an extra train to Stevenage.
 

jon0844

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They'll surely continue to go to Moorgate, and possibly become part of London Overground one day.

I must admit that, although the problems are pretty rare, when things do go wrong on the core it does make you wonder how the hell they're going to run trains from Brighton and thereabouts through and up to Cambridge or Peterborough - and to time, to fit around the other trains on the ECML.

Tomorrow morning, I'm off to Gatwick. I could go to St Albans by taxi and take a train straight through but instead I'm going to King's Cross and then over to St Pancras to get a train from there.

To be honest, nice as the link up would/will be, it's such an incredibly short and easy walk from King's Cross to St Pancras that I really don't think it would have been that difficult to keep trains going in to King's Cross and forget about the link!
 

Grimsby town

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My plan was to relocate the station to the south of the viaduct and have one platform on the up slow which would be bi directional and served by a half hourly secvice calling at Welyn Garden City, Hatfield, Potters bar, Finsbury Park and Kings Cross. The Cambridge stopper would go via the Hertford loop and Knebworth would be served by a half hourly service to Peterborough which would have Kebworth as it's first station after Finsbury Park.
 

MidnightFlyer

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My plan was to relocate the station to the south of the viaduct and have one platform on the up slow which would be bi directional and served by a half hourly secvice calling at Welyn Garden City, Hatfield, Potters bar, Finsbury Park and Kings Cross. The Cambridge stopper would go via the Hertford loop and Knebworth would be served by a half hourly service to Peterborough which would have Kebworth as it's first station after Finsbury Park.
So you'd have no services between Knebworth and Welwyn Garden City, Hatfield, Potters Bar etc?
 

swt_passenger

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They'll surely continue to go to Moorgate, and possibly become part of London Overground one day.
Why do you say that?

They are clearly intending to have 4 tph Welwyn GC slows diverted to Thameslink, it is stated in all the relevant RUSs. Moorgate is going to have a much enhanced service to/from the Hertford loop in lieu of the diverted services.

This has been discussed here quite a few times in the last few months.

--- old post above --- --- new post below ---

To be honest, nice as the link up would/will be, it's such an incredibly short and easy walk from King's Cross to St Pancras that I really don't think it would have been that difficult to keep trains going in to King's Cross and forget about the link!
You seem to be forgetting that you need destinations for 24 tph from south of the river. There isn't the capacity to send them all up the MML, so where do you suggest they go instead? You can't suggest Blackfriars bays, because their capacity is already taken by 8 tph terminating there anyway...
 
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jon0844

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That would seem rather odd, if not stupid. Who would want to be on an all-station stopper that goes through the core? It would take ages!

There are of course semi-fast trains that terminate at WGC in the peaks (to reserve paths over the viaduct) and I could see that these might go through. The only reason they currently have a few stops along the way is to stop them catching up with the slows from Moorgate, which they usually do by Potters Bar - and then crawl behind to allow the slow to stop at Brookmans Park and Welham Green.

If London Overground does happen, I am sure there will be trains to Moorgate AND trains to King's Cross (or beyond) which will fill out the slows quite considerably!

Edit: BTW, they may be planning to cope with 24tph but surely only in the peaks, so perhaps they won't be running that many slow trains throughout the day and into the night?

I am sure the plans will change anyway, as there have been discussions and quite often we get 'the current thinking...' posts which suggests nothing is fully decided. My comment about not bothering with the link was only opinion, not a serious suggestion that they don't do it!!
 

OxtedL

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The people who live at the stops where the all-stopper stops?

Southern for instance often reference demand for service extensions as being extant on the Sydenham line, where everything stops everywhere.

(Apologies if I have misinterpreted what is being said.)
 

Bald Rick

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It's been considered many times before, and it is difficult to make the case. Yes it releases capacity at this location, but there isn't the space elsewhere on the route (not least KGX) to make use of it.

Network Rail still own a few of the houses in the Mimram valley under the existing viaduct from when the last rund of proposals went through and locals got cold feet.
 

Grimsby town

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So you'd have no services between Knebworth and Welwyn Garden City, Hatfield, Potters Bar etc?
That's probably the only problem. It wouldn't be possible to go north from these places without going to Finsbury Park. Maybe stopping 1 of the Peterborough's at these
stations or just at Welwyn Garden City with good connections if the patronage is there as I imagine most people want to travel to London from these places
 

philjo

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That's probably the only problem. It wouldn't be possible to go north from these places without going to Finsbury Park. Maybe stopping 1 of the Peterborough's at these
stations or just at Welwyn Garden City with good connections if the patronage is there as I imagine most people want to travel to London from these places
A lot of people use the train to commute to work in WGC, Hatfield (also a lot of UNI students at Hatfield) or Potters Bar so you would still need direct services to Knebworth & Stevenage from potters Bar, Hatfield & WGC. Off-peak a lot use the train to WGC for shopping as M&S & John Lewis are a couple of minutes walk from the station.
 

RichW1

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Well, it is expensive to do this stuff I agree...if only we had cash surplusses like the Chinese or Brazilians. We really (on paper) need to build all of these things and we must remember several countries are just getting on with the job thinking 50 years ahead and more. I do get concerned. It may well be quicker to add to the debt whilst interest rates are so low and swallow the bitter pill (this obviously assumes the economy will grow). I don't know, I'm just putting it out there. I want a competitive UK plc in 2030 and after not a constrained one. But hey I'm thinking allowed here, nothing more.
 
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