DART+ (DART Expansion)

OisinCooke

https://www.boards.ie/discussion/comment/123600221#Comment_123600221

Very well put, and l agree wholeheartedly, a DART+ Tunnel that linked the Western and Southwestern Lines would be a poor use of resources and would not provide nearly as much benefit as a link with the Northern Line.

@murphaph put it very well. It should be built to link the two quad tracked (ie. separated DART and Intercity) spines into the city to allow for effectively a metro style DART service frequency-wise and allow for potential automation in future.

I’m afraid however that putting the northern tunnel at Fairview Park very likely wouldn’t work due to the now required deeper depth of Spencer Dock station and both the Tolka River and Port Tunnel both being in the way of the line rising above ground. It would also have to get high enough to bridge the Clontarf Road in a very short distance. Trying to avoid all of these obstacles would result in a gradient that would be much too steep.

I think avoiding a Clontarf Road station entirely and emerging above ground at Clontarf Golf Club before Killester would work far more comfortably. The only issue is it would add around 2km extra of tunnel length, but as @gjim mentioned, four-tracking all the way to Heuston means that the tunnel portal could be brought east by about 1.5/2km from the previous location of Inchicore depot, so would make the tunnel extension in the north a lot less expensive.

This also means that quad-tracking of the Northern Line may not have to start all the way back at Connolly. As the vast majority of Northern Line trains will be going straight into the tunnel, there may not be enough DART traffic between Killester and Connolly - aside from the odd service to Bray/Grand Canal - but nowhere near the level of conflict that will be present without the tunnel - to warrant separate running lines, so this would make FourNorth cheaper too.

In relation to a Heuston cut-and-cover station under the car park, this could work very nicely actually, and be tied into the station with a new underpass at the western end of the Heuston platforms, something which Heuston station could definitely benefit from. An exit could also be built to Heuston West, and too linked to the underpass, making it feel a lot closer to Heuston that it otherwise would and further increasing the overall DART+ Tunnel station inter-connectivity.

gjim

@OisinCooke - you're probably right that the golf course would be better.

Either that or Clontarf Rd would be FAR superior to branching off south of East Wall Rd, which would put a huge dint in possible frequencies/capacity because of the "crossing at grade in opposite directions" consequences.

Another advantage is that as part of the portal works, you could expand Clontarf to 4 platforms or build a new station at the golf club (replacing Killester) with 4 platforms allowing IC passengers direct interchange to DART N-SW. This was another failing with the old plan - Belfast/IC passengers would have had 2 changes to access stations along the DART N-SW and vice versa. While this way allows an interchange at Clontarf for DART N-SW or stay until Connolly for DART S-W - basically one change access for IC passengers to the entire DART network. Incredible connectivity.

And with the grade separation offered by such an arrangement, you could immediately offer 18 DART/hour before starting on FourNorth - leaving enough room for 2 IC slots per hour. A DART every 3.5 minutes is easily "metro level" service.

There's no need to consider digging up DART+W Spencer Dock - this was forced by old choice of location for the northern portal. You have plenty of choices now to swing further East for a docklands DART N-SW station.

This also gets rid of two complex and expensive underground stations from the old plan replacing them with a simple cut n' cover at Heuston and a surface station at Clontarf (Rd or Golf club). You'd still have the complexity of mined stations at Stephen's Green and either Pearse or GCD but for the initial project I'd drop the underground Christchurch and Docklands stations. Since these would require mining, so there's little benefit to bundling them into the initial tunnel project - they could be part of a follow-up project given that a 4 station DART-U achieves the goal of freeing the system from the Connolly.

This effectively creates 2 new metro lines crossing the city, and would offer one-change access from any of of about 80 DART or ML stations to any other - creating a genuine network and with metro-style "turn up and go" frequencies throughout the system.

AngryLips

If a Dart-U tunnel was built north of Fairview then what rail service will serve Clontarf Road station or would that station be mothballed? If all Dart services on the northern line are routed via DU then the only passenger services passing through Clontarf Road would be IC services to Belfast and Dundalk trains.