Fantasy - GWML west of Old Oak Common

[squingo44]

I've been looking at the GWML again, and gauging which sections of track looked reasonably feasible to 6-track. My answer is from just west of Langley to just east of Southall. The optimist in me would through in Hanwell and a rebuilding of the Wharncliffe viaduct, but I'm ignoring that for now.

It would be nice to build an express tunnel for the Elizabeth line from OOC to Southall, and 6-track from Southall to Langley. This would allow the services from Shenfield to serve as the Heathrow express services, while also allowing an express service from Reading to go non-stop between Slough and OOC.

You could have something like:

- 8 TPH Heathrow-Shenfield, express from Heathrow to OOC
- 4 TPH Heathrow-Abbey Wood, all stops
- 8 TPH Maidenhead-Abbey Wood, all stops
- 4 TPH Reading-Abbey Wood, express from Slough to OOC

And the finer details of the infrastructure interventions needed can be sketched in. Obviously a new Heathrow station would be needed, but it'll be getting a high speed station eventually anyway.

What do you guys think? Would it be better to build the tunnel for stopping services, and bottle up some of the stations on the surface line, so that freight traffic can interline with the express services rather than the stopping services?

 

[Mgameing123]

I've been looking at the GWML again, and gauging which sections of track looked reasonably feasible to 6-track. My answer is from just west of Langley to just east of Southall. The optimist in me would through in Hanwell and a rebuilding of the Wharncliffe viaduct, but I'm ignoring that for now.

It would be nice to build an express tunnel for the Elizabeth line from OOC to Southall, and 6-track from Southall to Langley. This would allow the services from Shenfield to serve as the Heathrow express services, while also allowing an express service from Reading to go non-stop between Slough and OOC.

You could have something like:

- 8 TPH Heathrow-Shenfield, express from Heathrow to OOC
- 4 TPH Heathrow-Abbey Wood, all stops
- 8 TPH Maidenhead-Abbey Wood, all stops
- 4 TPH Reading-Abbey Wood, express from Slough to OOC

And the finer details of the infrastructure interventions needed can be sketched in. Obviously a new Heathrow station would be needed, but it'll be getting a high speed station eventually anyway.

What do you guys think? Would it be better to build the tunnel for stopping services, and bottle up some of the stations on the surface line, so that freight traffic can interline with the express services rather than the stopping services?

It would be better if the main line was moved into the tunnels, then the current day mainline can be for semi fast and freight movements and the relief can be solely for the Elizabeth Line. Though I’d rather have that the new express tunnel went via Heathrow Airport that way Heathrow can obtain proper intercity train connections to the West of England and South Wales. It’s insane that the UK’s busiest airport has ZERO intercity trains.

 

[cle]

It would be better if the main line was moved into the tunnels, then the current day mainline can be for semi fast and freight movements and the relief can be solely for the Elizabeth Line. Though I’d rather have that the new express tunnel went via Heathrow Airport that way Heathrow can obtain proper intercity train connections to the West of England and South Wales. It’s insane that the UK’s busiest airport has ZERO intercity trains.

So express tunnels would be before / not include OOC? As two inter city stops before Reading would be nuts, but it will be a massive hub by then so some connections (notably HS2) would be missed. And even with one call at Heathrow, journey times would be back towards 30 mins on London-Reading.

Would you do Heathrow Central or T5 station?

I do love the idea of all Elizabeth trains extending beyond OOC on dedicated lines. You could do:

8tph T5 (two patterns)
4tph T4 (all stations)
6tph Reading (two patterns)
2tph Hayes bays for capacity - all stations
4tph OOC starters for capacity

 

[Bald Rick]

Six tracking was looked at in the late 90s. Didn’t get very far obviously, as it was horrendously expensive.

 

[MotCO]

How far from the current GWML will the third runway at Heathrow be? Could there be a slight diversion to serve the new third runway terminal, and would there be some sort of internal link from the third runway to the main airport?

 

[Mgameing123]

So express tunnels would be before / not include OOC? As two inter city stops before Reading would be nuts, but it will be a massive hub by then so some connections (notably HS2) would be missed. And even with one call at Heathrow, journey times would be back towards 30 mins on London-Reading.

Would you do Heathrow Central or T5 station?

I do love the idea of all Elizabeth trains extending beyond OOC on dedicated lines. You could do:

8tph T5 (two patterns)
4tph T4 (all stations)
6tph Reading (two patterns)
2tph Hayes bays for capacity - all stations
4tph OOC starters for capacity

Well no I believe the new tunnel should start after OOC and come back around Reading. Not all of it has to be tunnelled but by building a new dedicated short high speed line (Yes I’m aware it will be costly) then you can keep journey times roughly similar maybe even faster than today.

 

[squingo44]

Six tracking was looked at in the late 90s. Dism’t get very far obviously, as it was horrendously expensive.

Surely the runaway success of the elizabeth line shifts the calculus?

== Doublepost prevention - post automatically merged: 9 Sep 2026 ==

I think that an intercity high speed tunnel to Heathrow is inevitable, but I don't think it needs to be related to Elizabeth line expansion so I'm leaving it out of scope.

On second thoughts, I think that a tunnel for stopping services may be better than an express tunnel. This is because the relief lines on the surface are still going to carry freight, and therefore the EL services on the GEML are always going to be importing lots of scheduling risk by interlining with them.

Instead, we could have the tunnel between OOC and Southall be for stopping services, and rebuild Acton Main Line, Ealing Broadway, West Ealing, and Hanwell stations underground. This would have greater flexbility in their placements, so they can be built closer to concentrations of development.

In fact, I'd go so far as to say that the Elizabeth line should run 100% all-stops services through this tunnelled track, with the following timetable:

8 TPH Langley-Shenfield
8 TPH Langley-Abbey Wood
8 TPH Heathrow-Abbey Wood

With the relief lines running express services from Reading to Paddington, express between Langley and Old Oak Common. OOC presents a perfect opportunity for cross-platform interchange, but the Paddington station approach would require some reconfiguring so that the Elizabeth line tracks and the relief line tracks could be separated all the way to the Elizabeth line tunnel portal.

 

[irish_rail]

In my opinion the two biggest issues for the GWML right now are the poor state of the current infrastructure (which needs more and better maintenance), and also the ridiculously tight turnarounds at Paddington.
I've lost count of the amount of times I leave Paddington 10 / 15 minutes late due to the incoming set being late in, and this then inevitably snowballs into bigger delays as paths are lost further down the line.
If the turnarounds at Paddington where extended from the current 15 - 30 minutes, to a standardish 45 minutes (as was normal in HST days) I genuinely think you'd see a massive increase in punctuality. It would also make passengers life better as there wouldn't be the 5 minute scramble after the train is announced late, and would give the poor cleaners a chance to do their jobs at a reasonable pace!
In HST days it was relatively unusual to depart Paddington late. Nowadays, it's more or less the norm (on the trains I work anyway).

 

[Mgameing123]

Surely the runaway success of the elizabeth line shifts the calculus?

== Doublepost prevention - post automatically merged: 9 Sep 2026 ==

I think that an intercity high speed tunnel to Heathrow is inevitable, but I don't think it needs to be related to Elizabeth line expansion so I'm leaving it out of scope.

On second thoughts, I think that a tunnel for stopping services may be better than an express tunnel. This is because the relief lines on the surface are still going to carry freight, and therefore the EL services on the GEML are always going to be importing lots of scheduling risk by interlining with them.

Instead, we could have the tunnel between OOC and Southall be for stopping services, and rebuild Acton Main Line, Ealing Broadway, West Ealing, and Hanwell stations underground. This would have greater flexbility in their placements, so they can be built closer to concentrations of development.

In fact, I'd go so far as to say that the Elizabeth line should run 100% all-stops services through this tunnelled track, with the following timetable:

8 TPH Langley-Shenfield
8 TPH Langley-Abbey Wood
8 TPH Heathrow-Abbey Wood

With the relief lines running express services from Reading to Paddington, express between Langley and Old Oak Common. OOC presents a perfect opportunity for cross-platform interchange, but the Paddington station approach would require some reconfiguring so that the Elizabeth line tracks and the relief line tracks could be separated all the way to the Elizabeth line tunnel portal.

I mean wouldn't it be cheaper to make an express tunnel? You save building 5 underground stations.

 

[Bald Rick]

Surely the runaway success of the elizabeth line shifts the calculus?

Nope.

 

[Mgameing123]

Surely the runaway success of the elizabeth line shifts the calculus?

== Doublepost prevention - post automatically merged: 9 Sep 2026 ==

I think that an intercity high speed tunnel to Heathrow is inevitable, but I don't think it needs to be related to Elizabeth line expansion so I'm leaving it out of scope.

On second thoughts, I think that a tunnel for stopping services may be better than an express tunnel. This is because the relief lines on the surface are still going to carry freight, and therefore the EL services on the GEML are always going to be importing lots of scheduling risk by interlining with them.

Instead, we could have the tunnel between OOC and Southall be for stopping services, and rebuild Acton Main Line, Ealing Broadway, West Ealing, and Hanwell stations underground. This would have greater flexbility in their placements, so they can be built closer to concentrations of development.

In fact, I'd go so far as to say that the Elizabeth line should run 100% all-stops services through this tunnelled track, with the following timetable:

8 TPH Langley-Shenfield
8 TPH Langley-Abbey Wood
8 TPH Heathrow-Abbey Wood

With the relief lines running express services from Reading to Paddington, express between Langley and Old Oak Common. OOC presents a perfect opportunity for cross-platform interchange, but the Paddington station approach would require some reconfiguring so that the Elizabeth line tracks and the relief line tracks could be separated all the way to the Elizabeth line tunnel portal.

Nope.

Infact it's probably more expensive today than it was in the 90's. But yeah additional capacity in some form though is going to be neccesary thanks to the success of the Elizabeth Line.

 

[squingo44]

Nope.

Why not?

== Doublepost prevention - post automatically merged: 9 Sep 2026 ==

I mean wouldn't it be cheaper to make an express tunnel? You save building 5 underground stations.

If you're building a tunnel extending the Elizabeth line in the west, you want to be able to use it to extend Shenfield services. But you can't extend those services onto the relief lines without interlining GWML freight traffic, so they're going to have to go into the tunnel, and they can clearly only really terminate at Heathrow. You want the split between express and stopping services to favour stopping services, probably around 2:1 - or 16 TPH stopping, 8 TPH express. And you also want some express services to go to the outer stations - Slough, Maidenhead, Reading, etc.

Therefore to me, it makes sense that the stopping services go in the tunnel, and the express services interline with freight traffic on the relief lines. It's probably a much higher capacity arrangement, since with electric freight vehicles the express services and the freight services can basically run non-stop at the same speed.

In fact, I'd go so far as to say all Elizabeth line services should be tunnelled and all-stops to either Langley or Heathrow, and the express services stopping between Reading and Langley turn around at Paddington.

 

[Mgameing123]

Why not?

== Doublepost prevention - post automatically merged: 9 Sep 2026 ==


If you're building a tunnel extending the Elizabeth line in the west, you want to be able to use it to extend Shenfield services. But you can't extend those services onto the relief lines without interlining GWML freight traffic, so they're going to have to go into the tunnel, and they can clearly only really terminate at Heathrow. You want the split between express and stopping services to favour stopping services, probably around 2:1 - or 16 TPH stopping, 8 TPH express. And you also want some express services to go to the outer stations - Slough, Maidenhead, Reading, etc.

Therefore to me, it makes sense that the stopping services go in the tunnel, and the express services interline with freight traffic on the relief lines. It's probably a much higher capacity arrangement, since with electric freight vehicles the express services and the freight services can basically run non-stop at the same speed.

In fact, I'd go so far as to say all Elizabeth line services should be tunnelled and all-stops to either Langley or Heathrow, and the express services stopping between Reading and Langley turn around at Paddington.

I think you're misundstanding what I'm saying. I'm not talking about Elizabeth Line services. I'm talking about the GWR fast trains that run non stop from Paddington to Reading. It would surely be cheaper to put them in a tunnel, move the Freight and Semi Fast GWR trains on the current day main line so that the relief can be decidicated tracks for exclusive Elizabeth Line usage.

 

[A S Leib]

In my opinion the two biggest issues for the GWML right now are the poor state of the current infrastructure (which needs more and better maintenance), and also the ridiculously tight turnarounds at Paddington.

Would uncompleted electrification be third or lower?

 

[HSTEd]

I think you're misundstanding what I'm saying. I'm not talking about Elizabeth Line services. I'm talking about the GWR fast trains that run non stop from Paddington to Reading. It would surely be cheaper to put them in a tunnel, move the Freight and Semi Fast GWR trains on the current day main line so that the relief can be decidicated tracks for exclusive Elizabeth Line usage.

It may be cheaper to build a single (or double in a single bore) track tunnel for freight trains, which could be potentially operated without crew in the tunnel.

That might be cheaper to build given the much fewer (if any) lives at risk, allowing more relaxed safety approaches.

 

[alf]

if 6 tracking is too expensive how about building flyovers to get the 387 GWR EMUs off the down fast at 60 mph west of Langley instead of the 1950’s flat crossing at 40 mph that blocks the up fast track. And do the same with the up slow to up fast between Slough & Langley, flying over the down slow to stop delaying down Elizabeth trains & 40 wagon stone trains & 25 wagon loaded jet fuel trains.
There is room between the road overbridges that cross the line for the flyovers if electric train gradients like 1 in 35 are used. A 60 mph impetus will soon see them over the top & down the other side.

 

[cle]

Freight does have a few different locations though, like Colnbrook.

Fast tunnel is cleanest and simplest, with no stations and no Heathrow. Portals just west of Maidenhead.

Twyford station itself would need a little work but broadly you can six track on last easily after Maidenhead. Pointless tunnelling to Reading, it's a lot of mileage and open fields.

Heathrow instead gets a metro (double to T4 or close it / Picc only) - and increase the T5 service massively. More fasts/semis can now run, and Hayes could be well-used for western connections - whole new service patterns to eg Newbury and Didcot could exit out of Paddington now with faster Hayes and Slough calls.

 

[Bald Rick]

Why not?

Because it’s like saying that the advent of the latest Sky TV deal has shifted the calculus of Port Vale winning the Champions League.

In other news, the Government is completely broke. There is no money for even basic enhancements on the railway (electrifying to Oxford, for example). New tunnels under the GWML is pure space cowboy territory.

 

[HSTEd]

In other news, the Government is completely broke. There is no money for even basic enhancements on the railway (electrifying to Oxford, for example). New tunnels under the GWML is pure space cowboy territory.

Well..... if such a project allows radical increases in Elizabeth line service west of Old Oak Common..... it could bring in quite a bit more ticket income than electrifying to Oxford.

Elizabeth line ticket revenue was ~£670m in 2024/2025 and is reportedly still growing.

 

[London Trains]

Because it’s like saying that the advent of the latest Sky TV deal has shifted the calculus of Port Vale winning the Champions League.

In other news, the Government is completely broke. There is no money for even basic enhancements on the railway (electrifying to Oxford, for example). New tunnels under the GWML is pure space cowboy territory.

Here we go again, ridiculing people in the speculative section of the forum

 

[rmHawk765]

In other news, the Government is completely broke. There is no money for even basic enhancements on the railway (electrifying to Oxford, for example). New tunnels under the GWML is pure space cowboy territory.

I mean the government isn't broke at all, the railways are...

 

[Mgameing123]

It may be cheaper to build a single (or double in a single bore) track tunnel for freight trains, which could be potentially operated without crew in the tunnel.

That might be cheaper to build given the much fewer (if any) lives at risk, allowing more relaxed safety approaches.

A freight tunnel is probably alot more difficult when it comes to capacity. Under long streches of tunnels used by freight trains you're only allowed to run 1 train at a time.

== Doublepost prevention - post automatically merged: 10 Sep 2026 ==

Freight does have a few different locations though, like Colnbrook.

Fast tunnel is cleanest and simplest, with no stations and no Heathrow. Portals just west of Maidenhead.

Twyford station itself would need a little work but broadly you can six track on last easily after Maidenhead. Pointless tunnelling to Reading, it's a lot of mileage and open fields.

Heathrow instead gets a metro (double to T4 or close it / Picc only) - and increase the T5 service massively. More fasts/semis can now run, and Hayes could be well-used for western connections - whole new service patterns to eg Newbury and Didcot could exit out of Paddington now with faster Hayes and Slough calls.

In reality 6 tracking is only neccesary to Heathrow Junction. It's mainly between Heathrow Junction and the Elizabeth Line portal where capacity becomes a huge problem.

 

[D365]

Here we go again, ridiculing people in the speculative section of the forum

At least this is one of the better threads, in so far as it's labelled as a 'Fantasy'

 

[irish_rail]

Would uncompleted electrification be third or lower?

Well the horrendous performance of IETs on diesel due to most sets having engines isolated all of the time would be greatly negated with more electrification. But where the need is greatest (the almost exclusively diesel Penzance route) would also require the most expenditure and in my view would never happen.
Increasing turnarounds at Paddington on the other hand should be feasible for far less outlay than electrification or building new tracks / tunnels.

 

[squingo44]

Because it’s like saying that the advent of the latest Sky TV deal has shifted the calculus of Port Vale winning the Champions League.

In other news, the Government is completely broke. There is no money for even basic enhancements on the railway (electrifying to Oxford, for example). New tunnels under the GWML is pure space cowboy territory.

I don't disagree with you there. But since this is a speculative thread, I was hoping you'd understand that I'm not asking you whether this is a project we should be building right now, but rather whether it's a fitting vision for the future of the network. So the question of whether the government is broke isn't relevant to the question at hand. I'd like to hear something different from you for once.

So let me ask you again - do you think this proposal makes sense as a capacity extension of the GWML, for when such a project will eventually be implemented? If not, what do you see as the main alternatives?

 

[Mgameing123]

At least this is one of the better threads, in so far as it's labelled as a 'Fantasy'

I mean some form of capacity upgrade will need to happen at some point. I honestly suspect they would rather go the HS2 route and build a new dedicated High Speed line between Reading and Paddington (I obviously advocate for it to stop at a Heathrow station) because that way we can provide a capacity upgrade and a journey time upgrade,

 

[MotCO]

A freight tunnel is probably alot more difficult when it comes to capacity. Under long streches of tunnels used by freight trains you're only allowed to run 1 train at a time.

Is there a maximum length of tunnel through which diesel trains can travel? If so, since I assume most freight is diesel hauled, it would make sense not to send freight down the tunnel.

 

[Zomboid]

This is labelled as fantasy, so what I'd do is expand Euston HS2 to become the high speed hub for London (let's assume the eastern leg happens as well, so probably something like 16 platforms). Then 4 track it out to somewhere like Aylesbury and build a new line via Oxford Parkway (maybe with a station there, sadly it's a bit far for "Shin Oxford" to also have platforms at Wolvercote on the Cherwell/ Cotswold lines but that'd be ideal for the interchange) to join the GWML around Swindon. Should clear most of the fastest trains out to permit a bit more to run on the existing lines.

Obviously away with the fairies.

 

[zwk500]

Is there a maximum length of tunnel through which diesel trains can travel? If so, since I assume most freight is diesel hauled, it would make sense not to send freight down the tunnel.

Depends on what your ventilation is like and how much emission the diesels put out, and your air quality rules.

Normally restrictions on having trains in the same tunnel sections are to do with fire evacuations. Evacuating 1 driver will be considerably easier than evacuating a train with a full load of passenger.

The biggest reason not to send freight in a tunnel is that there's a hell of a lot of freight terminals connecting in (including Southall/Brentford branch on the Main Line side).

 

[PartyOperator]

I mean the government isn't broke at all, the railways are...

Why would a broke railway funded by a broke government have built a tunnel from OOC to Northolt?