DART underground - options

gjim

https://www.boards.ie/discussion/comment/123699964#Comment_123699964

The interconnector/DART-U or whatever you want to call it - going back to the original 1970s DRRTS proposal - was NEVER intended to carry intercity traffic.

None of the designs then or since - whether detailed or just studies - would have been capable of carrying intercity traffic. Just like every other heavy rail metro tunnel in Europe. This article - https://worksinprogress.co/issue/the-magic-of-through-running/ - explains the theory and background to DART-U. There’s no need to bastardize the concept.

Really can we start a separate discussion on through-running intercity services? Because it has nothing to do with DART-U - except that the rolling stock uses the same gauge. It reminds me of the complaints against the first Luas proposals back in the day - that their tracks should be able to accommodate DARTs.

AngryLips

https://www.boards.ie/discussion/comment/123700240#Comment_123700240

I'm not advocating for it. I'm just discussing the possibilities …such as, if the NTA wants to radically reimagine what a city centre interconnector would look like (which they might, given that the existing project is dead in the water), they might look at a connection that facilitates both IC and commuter services, one that accounts for both Dublin Airport and AIRR recommendations. A connection to Dublin Airport would improve the business case for a second northern line massively.

PlatformNine

https://www.boards.ie/discussion/comment/123699144#Comment_123699144

I would argue that it is really both that will cause capacity restricitons. Adding DU without 4N may increase capacity a little, but without flyover junctions to reduce conflicts, the total capacity of the line is going to be heavily limited before 4N.

Where does the 20tph figure come from? The highest TSS I have seen from IE for it was 15tph from some D+ reports, but that was DARTs only with Rosslare services terminating at Greystones. I fully believe the loop line can handle that but I would assume that is as a metro-like service operating between the Maynooth/Navan lines and southern line.

While I wouldn't fully agree that a four-tracked northern line would only be limited to 12tph, I have never argued that it would increase DART capacity, they would still be limited to 9tph due to capacity restrictions south of Connolly. Even then I am aware that if the northern line capacity is increased it's not going to be by a significant amount, likely only 1 or 2 services.

KrisW1001

https://www.boards.ie/discussion/comment/123700081#Comment_123700081

That one platform for on, one for off system is called “Spanish boarding”, as it was first used in Madrid.

Munich S-Bahn trains stop at platform for 30 seconds, even at Marienplatz, one of the busiest stations in the tunnel section (count for yourself in the video here: https://youtu.be/9MGDyRjXoao?t=775 ). Marienplatz is only “elaborate” because the station box had to have a very small footprint: as a result, the eastbound tube is above the westbound, and some movements between platforms are not possible (as every tourist finds out once as the escalator takes them inexorably down past the train they wanted to catch). Karlsplatz (next station west) is a far more traditional design with three platforms (two regular, one wide central) for two tracks, as is Hauptbahnhof (next again).

The other two tunnel stations in Munich, Isartor and Rosenheimer Platz, are quieter and do not use the Spanish boarding system , and none of the outer stations use it. Ostbahnhof (the first surface station on the eastern end of the tunnel) is a regular arrangement, although complicated because there are multiple S-Bahn platforms here for the diverging lines.

DART trains typically stop for 40-50 seconds at platforms, and this seems to be more due to scheduling than capacity. That’s my own limited experience, and I’d love to find video evidence of this, but all the train nerds edit out the time at platform from their videos... Acceleration of the rolling stock is a major determiner in how much time you can spend at station for a given headway, and the new DART+ trains are a tiny bit faster than the stock running in Munich.

The DART Underground was proposed as a twin-bore tunnel, which would not prohibit “Spanish boarding” being used on the underground stations: all of the proposed stations in Dublin are likely to be busy. I wouldn’t see a huge difficulty in achieving the same level of service, which in itself is actually far more than Dublin will need for a couple of decades.

plodder

https://www.boards.ie/discussion/comment/123701016#Comment_123701016

That's interesting. I didn't know that's what it was called. I knew that at least one of those stations had the one on top of the other configuration, but wasn't sure which. The fact that you can't exit the station if you get off the wrong side of the train, and can't even access the wrong one for boarding (as the escalators only go one direction) maybe was just a side effect of the design, but it must help to keep passengers that don't need to be in conflict, segregated.

I knew Rosenheimer Platz was an ordinary layout as it doesn't have any interchange with U-bahn. I remember it well, as I worked up the road from there a long time ago.

gjim

Where does the 20tph figure come from?

DART+ will have 10-12 DART coastal plus 8-10 slots split between DART+W and SW plus a couple of non-DART trains traversing the loop line last I heard. Signaling was upgraded a few years ago in advance of DART+ to allow 23 tph. Also 23 tph is the DART capacity of DART+SW.

Adding DU without 4N may increase capacity a little, but without flyover junctions to reduce conflicts, the total capacity of the line is going to be heavily limited before 4N.

It’s not a “little” - DU will double the North-South capacity of the system allowing up to 20 tph both for N-SW and 20 tph for W-S.

DU itself removes a large number of conflicts - specifically those between DART+W and DART+N entering Connolly from the North and those between DART+W and phoenix park tunnel DART+SW trains.

The primary benefits of 4N are supporting a decent IC service instead of having IC trains crawling behind stopping DARTs adding 20 minutes or more to journey times, providing improved reliability and operational simplicity - its contribution to DART capacity is very limited. Without DU it would provide NO extra DART capacity at all. With DU, you’ll get 3 extra slots per hour maybe.

While I wouldn't fully agree that a four-tracked northern line would only be limited to 12tph, I

How? Where are any extra 4N DARTs going to go? They either terminate in Connolly - an conflict nightmare - and very limited in terms of capacity - or else displace a DART W or SW crossing the loop line.

thosewhoknow

Would it be worth looking at making the tunnel big enough for double-decker trains if 4North doesn’t work out? (Or even if it does, just to allow for more capacity) I know that the current network isn’t suited for double-decker trains but I feel like it shouldn’t be too expensive if they’re just lowering tracks under bridges and platforms that only DARTs call at.

spark23

https://www.boards.ie/discussion/comment/123698970#Comment_123698970

Are the stations not being future proofed anyway with the platform length to allow for 2 five car Dart+ sets joined together as is possible, would be very foolish not to build some future capacity into the line. I can see the benefits of having Stephens Green as a larger future city center interchange even if not initially but future proofed to allow the possibility.

KrisW1001

https://www.boards.ie/discussion/comment/123701756#Comment_123701756

Inter city trains will never run on this tunnel. From the very first mention of a tunnel, it has been for commuter services. The costs are too high, the benefits too low.

And it's off topic here. Go to the "Cross Border Review of Rail Network" thread if you want to continue advocating for it.

PlatformNine

https://www.boards.ie/discussion/comment/123701439#Comment_123701439

DART+ will have 10-12 DART coastal plus 8-10 slots split between DART+W and SW plus a couple of non-DART trains traversing the loop line last I heard. Signaling was upgraded a few years ago in advance of DART+ to allow 23 tph. Also 23 tph is the DART capacity of DART+SW.

I don't believe that is correct. From the TSS diagrams I have seen, D+ Coastal South will support 15tph on the Loop line to GCD, with 12tph going to Bray. That is 3tph HH-GCD, 3tph to Maynooth-Bray, and 9tph (all DARTs) from the Northern line to Bray and Greystones. I will note I have seen two slightly different versions for services south of Bray. The first is from the D+W EAIR, Volume 2, Chapter 4 (link), and shows 2tph to Greystones with one service either continuing further south or as a shuttle (it doesn't specify). The second is attacthed to the D+N PC materials, Annex 3.3, Appendix C (link), shows 3/4tph to Greystones and a shuttle service from Rosslare to Greystones.

Also the DART+SW total capacity is 23tph, not the DART capacity. 12tph is from all the various fast line services, so ICs, regionals, and likely a few outer commuters as well. Then D+SW will support 11tph DARTs on the slow line, 4 terminating at Heuston, 4 terminating at SD via Drumcondra, and 3 terminating at GCD. I believe there isn't a 12th service due to terminal capacity.

It’s not a “little” - DU will double the North-South capacity of the system allowing up to 20 tph both for N-SW and 20 tph for W-S.

DU itself removes a large number of conflicts - specifically those between DART+W and DART+N entering Connolly from the North and those between DART+W and phoenix park tunnel DART+SW trains.

The primary benefits of 4N are supporting a decent IC service instead of having IC trains crawling behind stopping DARTs adding 20 minutes or more to journey times, providing improved reliability and operational simplicity - its contribution to DART capacity is very limited. Without DU it would provide NO extra DART capacity at all. With DU, you’ll get 3 extra slots per hour maybe.

Again, while I don't disagree that the tunnel will eventually allow for 20tph frequency eventually, I think it is going to have a hard time doing that without full grade seperation from non-DART services. It's not just that the IC services are getting slowed down, their different stopping pattern and fleet's physical characteristics also has an effect on DART services too. I think 15tph might be more realistic (12 DARTs + 2 Dundalk + 1 Enterprise) for a DU only network, but that comes back to my main critisism of DU before 4N, that I don't believe such a minimal increase in service would warrant the CBA.

It also might not remove conflicts with PPT services at either end of the tunnel depending on the fate of PPT services post-DU. They aren't building two new stations just for them to be shut down when DU opens, so either some services from HH will continue to use PPT or services will start at Heuston West, possibly depending on the design of the Portal. Eitherway there will be PPT tunnels going through Glasnevin Jnc. There are a number of other conflicts not solved by DU, not all of which even have a direct effect on DU frequency (Clonsilla Jnc for example), but their limitations will start to become more noticable when DU is complete and IE tries to push for higher and higher frequencies.

How? Where are any extra 4N DARTs going to go? They either terminate in Connolly - an conflict nightmare - and very limited in terms of capacity - or else displace a DART W or SW crossing the loop line.

They would have to be fast line terminal services. The D+ plan is for 5 services terminating in Connolly between its 4 bay platforms. 4N will allow services to move between the fast line and bay platforms without causing congestion for the slow line, and this should allow services from those platforms to operate more flexibly and more effeciently, potentially allowing for an additional Dundalk service or an express commuter service.