DART underground - options

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.

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.

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.

The long term plan is to move Sligo trains to Heuston via a new Maynooth to Hazelhatch link, 4 track the northern line and end Rosslare services at Bray so the whole DART network will have it's own tracks and no mixing with intercity. That'll give us a great core DART network that can comfortably accommodate spur lines like in the original DART plan from the 1970s. We souldn't then go start mixing in intercity trains again.

It also provides a better service to Islandbridge with the Heuston West stop.

No matter what way you slice it before DART Underground, Heuston is going to have to have a radical expansion to accommodate a doubling of all intercity services, DARTs every 15 mins and increased commuter service. It can go northwards over the river or southwards and tunnelize St johns road. I don't think irish rail have realised this though, they're still obsessed with selling or renting land for development not thinking how they're going to accommodate a dramatically increased service without adding more platforms.

If/when they made the Howth Branch a shuttle service, they should move the "Junction" station slightly north a tad, and and continue the Branch under the northern line towards the Malahide Road at Coolock and onwards to link with Metro North, it would then feed passengers into the DART and Metro lines from Howth/Sutton/Bayside/Coolock/Beaumont and the like.

There are no plans for metro 2.