DART underground - options

Where do you have 1100m to go from underground to over the DPT?

Your crayons, pedantry and snark have never been helpful to begin with.

See below which was shared previously.

Your aversion to crayons is rather baffling. This is a thread discussing future route options for a rail line...

I'm not sure what you are saying here.

What's the long term goal of Irish rail here? Once it's built, it will be politically infeasible to close it to passengers again. Do they think they can do this upgrade work during Metrolink shutdown?

That report is based on the DU station being under the DART+ station. If the DU station isn't under the DART+ station, then you don't have this issue. The DART+ station can be south of Mayor Street.

If the tunnel portal isn't at Docklands )at Fairview instead), the TBM route could avoid going under the DART+ station altogether.

The tunnel won't happen for a long time (decades), that is clear. The case for the tunnel remains valid and it will be revisited once the short-term solutions have reached their limitations.

It is extremely likely that the tunnel Docklands station won't be under the DART+ station but a large plot still exists south of the DART+ station. The new tunnel design will just have to utilise that site differently than originally envisaged.

On a slightly different take, I wonder how a CBA analysis would hold up on a second Metro line versus a revised DU. The main benefit of DU was East-West connectivity (correct me if that's totally off). If this capacity can be given with a high capacity Metro line, rather than a 1600 gauge heavy rail line (which may have to share capacity between Dart, Commuter and Intercity), then a second Metro line will win hands down.

Realistically, the cost of building DU with 170m long platforms might be seen as 'too prohibitively expensive' versus a second Metro line, given the 'relatively' constrained capacity of a 1600 gauge rail line versus Metro (driverless trams every 90seconds)...

In terms of construction cost, can someone confirm how the original DU stations were going to be built? The current Dart platforms are 170m long, so I assume DU would have had the same? The Metro platforms are much shorter at 80m, which will allow easier and cheaper cut and cover stations to be constructed.

The tunnel allows for a big increase in a capacity on the existing heavy rail network. We need to utilise and maximise the existing infrastructure. Metro isn't going be able to achieve anything like the same level of coverage or capacity from one line.

Once the DART+ projects are complete, the case for the tunnel will improve immensely. There will be four quality lines serving established population centres and brand new, modern rolling stock, new depot, etc. What it will need is the tunnel to tie the lot together and eliminate bottlenecks. We are talking one ~6km tunnel with huge benefits, another metro might cost less but wouldn't give anything like the same level of benefits.

Fair enough, but if you don't have the eastern portal in the docks, where would you bring it out? I can't see any other location that offers the same connection opportunities.

Just for information, the Western portal was at Inchicore, not Heuston: the Heuston DART Underground station was to have been built at the front of the mainline station, with entrances on street by the Luas stops and within the building itself. The actual station box would have been partially under lands owned by Diageo/Guinness.

@AngryLips A "Connolly North" station where the Western line crosses the Northern would be at Ossory Rd, just southeast of Croke Park. However, that location is 500 metres from Connolly station, which is too far for an "interchange" - it's exactly the same distance from Connolly as the current Docklands station is.

(a station serving Croke park is worth investigating in its own right, though)

The problem is walking distance. An interchange station connects two lines, so ideally you want the walking distance from one to the other to be close together. 500 metres is not "close": for comparison, O'Connell Street (upper and lower) is 560 metres long

I suppose that depends if you're including Dart+ Tunnel in the "Full Dart+ Projects" label!

I think with some intelligent placement of station entrances you can 'get away' with certain layouts, especially if you add things like travelators/escalators to pedestrian access tunnels. These often feel like they (psychogically at least) don't count as 'real' distance.

I threw together a crayons route that I feel could work and get you enough height around the Tolka and Port Tunnel.

Included some proposed station entrances as well, route is very rough, it's going to assume all stations with the "possible" exception of Spencer Dock are going to have to be mined out, Heuston could maybe be done cut and cover if the whole thing was in the road, but I can't imagine them closing that for the duration of constriction...

https://www.google.com/maps/d/u/0/edit?mid=1B8bR1J7U6FSsXG9j-QvKvlC4lenWbkE&usp=sharing

interchange stations would be extremely close to both Connolly and Docklands. Also if you were going to build a new station between Drumcondra and Docklands, around Ballybough would make more sense.

I think the best place for the eastern portal would be immediately west of the Tolka and north of ABR, then rising to connect to the Northern Line east of Clontarf Road station. An underground station at Docklands could be built south of Mayor Street, giving that connectivity but without all the other hassle of creating a tunnel portal there or disruption at the DART+ station. Obviously engineering assessment would be needed to ensure the tunnel portal at Fairview is possible but if so, but that applies to every suggestion.

And just for information, the latest options report had the Western portal at Good Counsel GAA Club beside the Chapelizod bypass, not Inchicore. It also has the Heuston underground station under the existing station.

Re: a route over the DPT, if you did a rising curve popping above ground just after the tracks into the docks, curving around following the dock road, then up over Tolka, DPT and tying into the northern line (refer to my map above and previous suggested drawing in the thread for the concept) then you're looking at a rise of around 14m over 1.3km (0.6°) of a rise to clear the tunnel top, even going more extreme to try and set up a proper flying junction into the northern line here (not sure on curves needed for that, but let's assume we need 7m of clearance above the track height (13m approx)) leaves a gradient of 1.02°