DART+ (DART Expansion)

@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.

Putting the portal anywhere near Heuston is a non-runner. The place @gjim mentions is a particuarly bad pinch point:

Trying to put a proper, grade-separated portal here would be hugely disruptive, and getting from ground level here to the depth needed for the Heuston deep DART station would need a fairly steep gradient of close to 3%.

Building it at Inchicore might add the cost of more tunnelling, but it wouldn’t have anything like the operational headaches during construction or commissioning, and would allow a more streamlined, faster approach into the Heuston deep station.

One nasty problem with trying to extend the tunnel beyond Fairview is that there is no way to do this without crossing the M50 tunnel. Worse is that you’re trying to cross that tunnel while trying to ascend to surface level. The M50 is not deep enough here for the railway to go over it.

The angle of the curve necessary to get between Connolly and Pearse and Stephen’s Green would be too sharp I think. While a stop at Connolly would be nice and would really make this an all-rounder of an underground link, I don’t think it’s doable or all that necessary

The DART underground tunnel per the offical plans was to surface within Inchicore, and then remain subsurface to join the Dublin Cork mainline with via an underpass

Heuston was ruled out long ago, the NTCC building is built on top of the previous location for the portals

I missed this before but none of those things sort out Connolly?

Implement all those things a you'll still be limited to 12 DARTs an hour entering the city from North coastal and limited to 8 DARTs an hour from DART+S and DART+SW through the centre.

How will electrifying the Enterprise do anything? The Enterprise doesn't hold up DARTs, it's the exact opposite - DARTs slow down the Enterprise. If the Enterprise, IC and all non-DART trains disappeared overnight from coastal North, the alignment would still be limited to 12 DARTs/hour.

Same with DART-SW and DART-S - the bottleneck is not the IC traffic, it's the lack of capacity through the centre.

That was a response to the video posted which explained why movements into, out of and through Connolly cause delays. The video explains the problems very clearly.

Enterprise particularly blocks multiple paths as it exits, Sligo line commuter trains also do so, as does the Rosslare service.

The limit of 12 tph, 5 minutes per train, is in part due to these conflicting movements regularly putting whole paths out of action north of Connolly. Remove and reduce these conflicts, and you increase throughput.

"The limit of 12 tph, 5 minutes per train, is in part due to these conflicting movements regularly putting whole paths out of action north of Connolly. Remove and reduce these conflicts, and you increase throughput."

No you're synthesizing facts here. Those conflicting movements are a disaster for reliability but the 12 t/h limit comes from the loop line bridge being limited to 20 t/h - 12 go to the coastal DART service and 8 to be shared between DART+W and DART+SW. So even if all IC traffic disappeared from Connolly this simple arithmetic would still apply.

The pinch point is that you cannot build something using just the footprint of the final structure. The less space you give, the more it costs and the longer it takes... there really isn't space on site to build this unless you close lines.

The platforms must be level. This is non negotiable.

8m depth means Cut and cover. That seems cheap, if you're happy to massively disrupt the operations of Heuston for the long construction period.

The idea of a portal at Heuston is dead ever since they built the train control centre. There just isn't enough space on the site to do tunnel now without screwing up the operation of the station. Inchicore won because it wouldn't disrupt revenue service during construction, and it allows a higher speed entry and exit.

This is an expensive build no matter how you slice it. Penny pinching around the edges won't save much, but will reduce the value of the final project.

Re: the Connolly comment, capacity of the loop line is not fixed in stone. There isn't much you can do about speed, but the resignalling of the line will reduce headway, potentially raising throughput. The key is to have only DART trains on this segment.