DART underground - options

gjim

https://www.boards.ie/discussion/comment/123151982#Comment_123151982

That doesn't work.

After DART+ there is zero capacity for any further DART services.

Spencer Dock max is 12 tph. You can't funnel DW and DSW trains into Spencer Dock without more than halving the services on both.

The problem is simple arithmetic.

Spencer Dock - max 12 tph.

Loop Line - max 22 tph.

Hueston - not sure about this but less than 12 tph for sure.

All of these slots will be fully utilized during peak after DART+. The point of DART+ was to absolutely maximize the capacity of the system WITHOUT DU.

This means we have the capacity coming into Dublin along the four alignments which cannot be used. For example, DSW is capable of 24 tph according to IE but this capacity will effectively lie idle until DU.

If anyone thinks there's a credible alternative to DU in order to provide central capacity, I'd be happy to hear it.

gjim

https://www.boards.ie/discussion/comment/123151253#Comment_123151253

It won't be possible to terminate trains from the north, whether DART or intercity in Spencer Dock.

The link with the northern line will be for non-service train movements only. Having regular service trains merging/splitting at grade north of Connolly would kill DN capacity. This is the same reason why Howth has to be turned into a shuttle service.

And even if you had fully grade separation, Spencer Dock only has the capacity to serve 12 arriving tph, all of which are required for DW and DSW.

gjim

The same problem has been examined over and over again in study after study since 1972 and despite efforts to come up with something cheaper/simpler/alternative/etc. every single time some variant of DU gets identified as the only realistic solution.

And it's not at all surprising because it's almost the exact same solution every other European city in the same situation has arrived at - cities which are decades ahead of Dublin in terms of rail PT.

You have two legacy heavy rail alignments which terminate at the edge of the city. So you tunnel between them to create a single through-running alignment, and then run high frequency services. The value proposition is that a few km of tunnel in the centre allows you to create a high-capacity high-frequency line that can stretch to 80km in some cases while offering metro-like services in the core. This has been done over and over across Europe. It works wonderfully.

For Dublin, the added benefit of unlocking DSW with DU is the potential for housing development given how poorly used or underdeveloped the land around the alignment is - so much low-density light industrial or literal fields - and that's just inside the M50. High density housing around Kylemore would be only 6 minutes by DART to Stephen's green for example. Even Park West to SSG would be 10 or 11 minutes.

scrabtom

https://www.boards.ie/discussion/comment/123153171#Comment_123153171

There is such potential for housing on the Dart South West line. Between the area around Hazelhatch/South of Celbridge, Adamstown, clonburris, the kylemore section of city's edge, the inchicore rail works and the Heuston masterplan I reckon there's the potential to house another 100,000 people directly adjacent to the rail line.

AngryLips

https://www.boards.ie/discussion/comment/123149385#Comment_123149385

This is a good point. If you were to deliver DU as a Metro line, then you could link it up with Red line services beyond Heuston and upgrade the whole way to Tallaght as a fully segregated metro service, similar to the plans for Green line and Metrolink. And as for what would happen to the city centre section of the Red line, well Lucan luas has a bit of a question mark over where it will go once it gets into the city centre…

CatInABox

https://www.boards.ie/discussion/comment/123154083#Comment_123154083

The constraint on the levels of service is the requirement to terminate trains in the city centre. A metro version of Dart+ won't get around this issue, and will leave the existing dart tracks underused compared to their possible capacity.

I still believe that they'll really try and reduce the costs on this whenever it breaks cover again. Single stop in the city centre, probably around SSG, is likely.

riddlinrussell

Given the need to Mine D+ stations regardless, would it be the worst thing in the world to only have one intermediate stop, at least initially? I'd imagine it would dramatically reduce the build cost?

Future proof the likely sites of additional stations by doing platform level basic prep that would be a major challenge alongside a live running system, and then add them in after the fact?

murphaph

Even a single station at Tara to interchange with the other DART line and metrolink would be revolutionary. The vast majority of DU passengers would likely change at Tara or alight there if it was so built. Doing some prep-work to allow later addition of one or two stations would be a bonus. I still think we should be more ambitious and just build the tunnel with 3 or 4 deep level stations + one in the docklands.

riddlinrussell

A Tara/College Green stop would be the best option in a single station setup, given the platform lengths you can have entrances at both to the same platforms, capture core destination and interchange at once, while adding interchange with the Green line

gjim

https://www.boards.ie/discussion/comment/123154083#Comment_123154083

I wouldn't be a fan of this idea even ignoring the fact that it does nothing to solve the problem of core capacity for DART and is completely unrelated to DU.

If we're going to build a new metro line, then it should be a completely new alignment, yes starting in Tallaght but through the city centre and on towards/past Coolock area. Absolutely no need to rip up the Red line and tear up half the Naas Rd. The Green line is completely different as Luas south of Charlemont is already almost completely grade separated. Anyway there's a separate thread for what metrolink 2 should look like.

KrisW1001

https://www.boards.ie/discussion/comment/123155927#Comment_123155927

Tara’s not a huge station to be using as a DART/DART/Metro interchange point. If there were to be a single intermediate station, I’d put it at Merrion Square, with tunnelled links to connect to Pearse DART and St Stephen's Green Metro. Something like this:

CatInABox

https://www.boards.ie/discussion/comment/123157700#Comment_123157700

Tara St is already one of the busiest stations in Ireland, and that's before Metrolink arrives. In my opinion, it'd be a total no brainer to have the station there, in terms of connectivity it's by far and away the best location.

The problem is that it's almost impossible to get from there over to the Docklands Station/Spencer Dock, with the right orientation for joining the Northern Line (i.e. almost North/North West).

Realistically, at least in my opinion, the line will have to swing south so that it can orientate correctly, which, like the old Dart Underground plan, will mean the line will cross the Metrolink and Dart lines at SSG and at Pearse respectively. In an ideal world, a station at both locations would be best, but I could definitely see them going for just the one station at SSG.

I still think that they'll half the train length and double the frequency, which will mean shorter stations as well.

riddlinrussell

Wont we have the new DART stock for the next 40 odd years? Unless you're giving up hope of Dart Underground for the next half century then it will be designed to fit that rolling stock?

scrabtom

What would the station at Heuston look like?

Would it be mined out directly below the main station?

You would assume there would have to be significant disruption when constructing the tunnel portal at the very least.

CatInABox

https://www.boards.ie/discussion/comment/123158241#Comment_123158241

The new Dart stock is designed to be run in either 5 or 10 car sets. What I'd propose is that any train that goes through the tunnel would be a 5 car set.

It'd mean that they'd only need to mine out 90 metres or so, the new five cars sets are 82 metres long.

CatInABox

https://www.boards.ie/discussion/comment/123158371#Comment_123158371

Yeah, Heuston is going to be tricky no matter their approach. Original plan was to do the tunnel portal in the Inchicore Works, but I believe that the location is no longer possible (I cannot remember why, nor am I sure that it can't be done.) Either way, the Dart+ project is electrifying the two northern tracks, so any tunnel portal would presumably be on the northern side of the track now, so as to reduce conflicts.

The original plan was to then do a mined out station south of Heuston.

Really not sure of how they'd do it now, to be honest. It's all gotten very tight around there.

Really spitballing here, I don't know enough about either the space required or the space that's there, but could they do a tunnel portal between the new Heuston West station and the new National Train Control Centre? Or even south of the NTCC, into the car park there? Both of those would have issues with conflicts with the PPT trains, but would avoid conflicts with main line trains.

A tunnel portal before all that, going under the War Memorial Park, with a cut and cover (assuming that the tunnel wouldn't be too deep there for cut and cover) station around the car park? It'd reduce conflicts to the minimum, and would be cheaper than mining out a station there.

As I said, it's a tricky problem.

Kaisr Sose

https://www.boards.ie/discussion/comment/123142820#Comment_123142820

And don't forget the retrofitting if energy upgrades to existing housing stock..As you and many others say, where do we get the labour from?

I am not really au fait with the whole thread. I dont know what the issue is with tunnels in this country..All over Europe they solve transport problems, be it urban or through mountains, but in Ireland, they the problem.

At this stage, doing anything would be better than endless discussion about doing something. In my opinion, it's already 20+ years late.

specialbyte

https://www.boards.ie/discussion/comment/123158746#Comment_123158746

Original DART Underground had planning permission for the tunnel portal at the Inchicore Works. This involved closing the works and moving the depot elsewhere (Portlaoise AFAIR). This was also when the track layout for the four tracking section was fast-slow-slow-fast.

With DART+ Expansion the track alignment is now slow-slow-fast-fast with the slow tracks on the north side of the mainline to avoid cross over conflicts for the DARTs entering the Phoenix Park tunnel as part of DART+ programme.

The DART Underground Western Tie-In Study (2017) recommended the tie-in be relocated to by the junction of Con Colbert Road and Chapelizod bypass. The main advantage of this was that it was a shorter tunnel that was cheaper to construct. It also nicely aligns with the DART+ plans of the slow tracks being on the north side of the mainline (though that isn't called out in the report).

This Tie-In location was re-affirmed in the October 2021 DART+ Tunnel options report that considered the impact of MetroLink on the DART+ Tunnel. That report that concluded we should do the original DART Tunnel alignment in the city, integrating with DART at Pearse and MetroLink at Stephen's Green.

The huge advantage of the Con Colbert Road DART+ Tunnel tie-in location is that we can do all of the work around 4 tracking for DART+ SW etc and the vast majority of the works needed for that dovetails nicely into the DART+ Tunnel Western Tie-In plans.

scrabtom

https://www.boards.ie/discussion/comment/123158746#Comment_123158746

This is what it says about building the station for Heuston in the 2021 feasibility report. They have it directly below the main station.

specialbyte

https://www.boards.ie/discussion/comment/123159148#Comment_123159148

I wouldn't put too much weight on that part of the report TBH. That part of the report was about determining was a Heuston station even possible given each options portal location. Many of the portal options had extremely poor options for Heuston when the portal was located closer to the Heuston rail yard.

With the tie-in at Con Colbert Road/Chapelizod bypass in Inchicore there are many options for Heuston station. It's about 1.75km from the portal to Heuston station. You need a ventilation/intervention shaft or station every 1km to meet modern fire safety guidance. So you need an intervention shaft between the tie-in and Heuston station somewhere anyway. That gives you some flexibility (+/-300m) on the placement of the Heuston underground station. It could be under the existing station, under the R148/outside St Stephen's Hospital or under the Guinness brewery lands and be within 2km. Lots of factors to weigh including constructibility, costs, disruption to existing uses, transport interchange distances etc. Something that any active DART+ Tunnel project would need to consider a fresh.

CatInABox

https://www.boards.ie/discussion/comment/123158979#Comment_123158979

Thanks for that post, incredibly informative, and it's good to see that they've already looked at a lot of this. Also good to see that the tunnel portal on the northern side of the tracks is viable.

On the station, as specialbyte says, I don't think that they'll limit themselves when it comes to DU, they'll essentially be starting again, and will look over the requirements/data all over again. From how they've designed Metrolink, and their desire to reduce the number of mined out stations, I really think that they'll design any station at Heuston to be Cut and Cover as well. It's this desire to reduce costs that makes me think that there'll be only on City Centre station, as it'll have to be mined out due to the depth. That won't (or probably won't) be a constraint around Heuston, as the tunnel won't need to be as deep there.

murphaph

Personally I see the Heuston Station station as being fairly straightforward in an international context. Between Military Road and Steeven's Lane there is a ramshackle collection of 70's era government owned buildings (Revenue, HSE, Garda) that could easily make way for a station. Likewise anything in the Docklands should be very straightforward as there is ample room. Personally I see a lot of merrit in the above suggestion to replace Stephen's Green and Pearse with a single station under the western side of Merrion Square, linked to the aforementioned stations by underground passage way. 200m by travellator is nothing. One mined out station somewhere around Christchurch and we are done.

KrisW1001

Cut and cover at Heuston will be increadibly disruptive, as any location for the station box is already occupied by a busy road, or by rail or Luas tracks.

Mining is much more expensive, but it has the advantage of not disrupting what's above, except for the construction of entrances and exits.

Cut-and-cover on this scale is really, really messy. This is half of Marienplatz S-Bahn station in Munich, during construction and how it looks today:

Marienplatz does have a small set of shops and an ticket office at its top floor underground, but that’s not why the build was so big. In fact, it’s a smaller footprint than the other stations: to fit the station-box into the available space, the east and west tracks (and thus platforms) run one above the other here, rather than side by side.

mackerski

https://www.boards.ie/discussion/comment/123160082#Comment_123160082

It’d be some crack trying to get permission for a tunnel underneath Government Buildings.

specialbyte

https://www.boards.ie/discussion/comment/123165736#Comment_123165736

It's not that wild. MetroLink passes directly under the length of Leinster House and pretty close to Government Buildings.

Zebra3

https://www.boards.ie/discussion/comment/123165748#Comment_123165748

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CatInABox

https://www.boards.ie/discussion/comment/123160198#Comment_123160198

There's a large car park at Heuston that'd be ideal for a cut and cover station, without much disruption at all.

It's hypothetical of course, but I don't see the NTA moving away from the principles that they've chosen for Metrolink. Cut and Cover wherever possible, with a focus on ease of construction.

KrisW1001

https://www.boards.ie/discussion/comment/123166679#Comment_123166679

DART Underground has to cross the MetroLink alignment somewhere near St Stephen’s Green, and stations are proposed within 200 m of that crossing point. There’s no alternative to mining in this case: the Metro tunnel is too close to the surface for DU to go over it, so it must go deeper.

Building under the Heuston carpark could be done as C+C, and while it is also possible in or around Christchurch, it’s not really feasible: digging out here would require closing several road arteries into the south inner city for several years. Any Pearse/SSG station has to be mined, and then Spencer Dock could be C+C or mined, but doing it as C+C basically requires closure and rebuilding of the station that will be built as part of DART+ West

CatInABox

https://www.boards.ie/discussion/comment/123166899#Comment_123166899

Yeah, that's why I said wherever possible. I've also said previously that they'd try and get away with as few stations as possible.

A Cut and Cover station at Heuston, a mined out station at SSG, and a station at Docklands, would be my guess on what they'd do. No station at Christchurch.

People have suggested a station at Merrion, with pedestrian access to both Pearse and SSG via an underground tunnel to each, I cannot see this happening. They really do not like mining out tunnels by hand at all, which is why I think they'll remove as many mined out stations as possible.

murphaph

https://www.boards.ie/discussion/comment/123166899#Comment_123166899

Just on a point of order, whilst I agree that platforms of that length will surely see two mined stations in the city centre, it would actually be technically possible to re-open those road arteries after a few months, not years, if they did choose to go cut and cover. Bailey bridges could be constructed over the excavation pits once they get going on them. Would that be preferable to mining? Probably not.