Cheap Tunnel

Rather than the billions they're talking about, why wouldnt they just drop a tunnel onto the floor of the Liffey, no tunnelling of note, no CPO, save a fortune, get you from Hueston to Tara Street in a jiffy, 2 pedestrian tunnels from IFSC and Tara Street side. You can catch the Luas on both sides of the river.

Or why not link the red & green line Luas further out of town, like along the canal, so you could get to Stephens Green from the Red Cow without having to go into Hueston. The tunnel must have been on the premise that Dublin is Manhattan, which it aint & never will be. You'd think they should crack on with a rail link to the Airport & stop with all the crazy stuff.

And a Limerick Cork motorway should be top of the infrastructure list - the €40M they already wasted on this craziness would have been a decent start.

I'd imagine a sunken option would likely cost a lot more. A tunnel just dropped on the river bed would rise well above the current road level. Sinking it would require dredging millions of tonnes of material, a dredger wouldn't be able to access most of that section without removing all bridges. Then you have the issue of trying to move massive tunnel sections into place, removing and re-building all the traffic bridges.

I think a lot of the thinking behind the tunnel option is they're trying to improve public transport infrastructure but are afraid to cause too much inconvenience to car users in the city centre.

Aside from the cost and difficulty of "dropping a tunnel onto the floor of the Liffey" (leaving aside the basic engineering considerations, have you considered the flooding possibilities of that? Or what about the effects on the city's sanitation?), it wouldn't fulfill a large part of the reason for having the tunnel interconnector. The purpose of the tunnel is not simply to connect the Heuston network to the Connolly network, though that is a key objective, it is also about bringing people to the optimum city centre destinations within the southside. If it was simply about connectivity between the two the existing Phoenix Park tunnel line would have sufficed. That is being prepared to accept passengers starting next year but it will not provide a suitable replacement for the Dart interconnector.

Ok, we're leave the liffey with a fast boat....

Connecting the Luas lines along the Grand Canal would get the people to the premium spots, this tunnel seemed Rolls Royce, for what it was going to actually do.

Luas connection would not suffice. It does nothing for the heavy rail infrastructure (and that is what the point of the interconnector is). It does nothing to connect Heuston and Connolly and it does nothing to relieve the constriction caused by Connolly station itself.

Dart Interconnector is actually not an overkill, it is actually necessary but the cost of it is high because tunnelling is not cheap and there is no overland corridor that can be used (going back to your point about the canal - that does provide a corridor that possibly could be used if we filled in the canal and put rail lines in instead, however it is restricted in terms of footprint and would adversely affect the city in other ways, the Luas already runs along a stretch of it, it is an amenity in itself and is used and it is one of the major cycle routes in the city)
It is probably more necessary than an airport connector but is far more of a risk still in the current economic climate. It is an expensive project, and was designed with the intention of maximising future capacity (larger tunnels for example) - call that a lesson learnt.

The harsh truth is though that there was only ever going to be a one or the other option between the airport connection and the Dart Interconnector. The airport connection is cheaper, will come on stream sooner, will have better optics with the public and the recommissioning of the Phoenix Park Tunnel will allow at least some commuter connectivity into the city though it does little for the Connolly conundrum. The Dart Interconnector was always only part of a plan that also involved extending electrification and reconfiguring city centre heavy rail services - just building the tunnel would not realise the true benefit of the project.

I thought the Phoenix Park Tunnel should do the "heavy lifting" of connecting Hueston & Connolly, plus you have the Luas that does that and if there was better integrated ticketing that wouldnt seem like such a hassle (for instance in London you regularly catch 3 tube lines to get somewhere - and between escalators and walk arounds in London, the stroll through Hueston to meet the Luas isnt that big a deal). Re the canal, couldnt you do an elevated track overheard the canal, keeping the amenity. Sure it cant be more than about 1.5 to 2 miles from Dolphins Barn (or thereabouts) to the Barge pub.

Most other countries are removing elevated rail lines. High Line in Manhattan is an interesting legacy of their elevated system.

The point was to NOT connect directly to Connolly. Connolly is already a pinch point. Dart Interconnector would have moved the connection pivot away from Connolly.

At the moment in London they are building a tunnel across the city to connect East to West and one of the primary drivers for that is you don't want to dump a load of people off heavy rail onto the Underground for the purposes of crossing the city - it is not a good thing, integrated ticketing or not. Just to note there is already North-South connection in London.

Elevated line along the canal would not retain the amenity value. You would have to provide a link across Inchicore from the main line (and of course that would most likely have to be a tunnel) and then you would have to build and maintain the same structure in a very confined footprint close to the Luas line and major road and cycle routes.

The route would also pass south of the city.

I suspect it was definitely aired as a possibility but I doubt it was ever a runner.

I'm incredulous that the Limerick to Cork road gets ne'er a mention in the Government splurge (& I've looked at the official doc, not the press snippets). Surely connecting ROI's 2nd & 3rd cities would make the bleedin' list anyway. Noonan, Coveney - are yis awake at all???

Forget about Limerick/Cork /Dublin.
In Letterkenny we need our 2nd bridge to show off our tidy town !