FourNorth - Quad Track Railway - North Dublin

I'd wager that there are absolutely no technical issues about quad tracking the northern line. Building retaining walls is bread and butter stuff for civil engineers. It's purely a money thing. It has to happen too.

Has there been any updates on the 4N feasibility report? Last I heard it was supposed to release sometime in 2025 but obviously that hasn't happened yet. At the very least I would hope it's getting close to publication?

I do agree with a lot of what has been said though, it will be a lot of work, but I doubt there would be anything seriously technically challenging.

If I had to guess the most notable works are going to at Howth Jnc. and Kilbarrack. The former I don't think would be technically challenging, but I think would be the single largest sub-project, as it almost definitely involves a major rebuild of the station. With plenty of space around the station I am hoping it wouldn't be too difficult to expand the station to 6 platforms, but either way platforms 1 and 2 can't survive as they are now. Kilbarrack however does concern me the most as I am not quite sure how they will approach it. No matter what though, a few houses would need to be knocked and even then, I doubt they would propose a 4-platform station, probably something more like the proposed Kylemore Rd Station.

For being a listed structure, I would have liked for it not to be covered in ads. I should have known it was a listed structure, that doesn't surprise me, but imo ads on a listed structure is just shameful.

From an engineering perspective I am not sure how they would solve that other than just building a second visibly identical bridge next to it? Hopefully that won't be a problem.

It won't be possible to excavate and build retaining walls when the only space you have to work on is a steep slope, literally up against a busy rail line with overhead electrical wires and little to no access for long stretches.

This is off-topic for this thread and should be discussed elsewhere but using the Google maps measure tool in this case is the height of naivety.

Not going to get into a big discussion on this as it is off-topic but weekend closures would achieve nothing. You couldn't operate any machinery that close to the operational rail line and live electrical cables. Even with full closure every weekend, it would take a decade. You'd get very little down in a weekend with it so spot/start, and you have to do both sides. That's assuming you can do such heavy engineering works with affecting the power supply, signaling cables, drainage, etc. needed to allow trains to continue operating at all.

Sheetpiling would have to be done from the top given the height of the embankment but there is no flat working space there. To sheetpile from the bottom, you'd need a very big machine and you'd have to remove all cables and supports for it to operate. But in reality, it would be unlikely to be sheetpiled, more likely a permanent contiguous piled wall, which would also be a large machine and would need a level, safe working space at the top of the embankment, which could only come from every garden bordering the rail line.

And that's before you actually start excavating anything, which obviously can't be done from on the slope itself. And all spoil excavated has to be taken away and new materials brought in, so you need access to the public roads, which is a few narrow bridges several metres above the trackbed. So at each bridge you'll need a ramp for trucks to drive up/down.

People here are seriously underestimating the scale of the works required.

DART+ between Parkwest and Heuston is not comparable to between Killester and Raheny. Parkwest to Heuston has working space and full accessibility along the northern side as far as Inchicore. Then there is the CIE owned Inchicore works to the south. A track may have to be closed to allow for working space on the trackbed, while rail operations continue on the other two tracks. They'll probably put up hoarding to separate the works area from the railway. You also don't have OHLE to worry about which significantly reduces the risk of operating machinery based the tracks and makes closing and reopening a track easier and quicker.

West of Inchicore is more constrained but is generally wider and less steep embankments. That whole section needs to be reengineered anyway, including adjusting trackbed, realigning tracks, OHLE cables and supports, new signaling and drainage, etc. Even if not widening, you would still have major works there just more electrification so including the widening works doesn't add hugely to the complexity or disruption.

And I didn't say that additional tracks on the Northern Line was impossible but it would involve significant disruption to rail operations and major CPO of private houses. I suspect that the report will say lots of things are possible but the full impacts of them would have to be assessed in further detail. Basically kick the can down the road in the hope the consultant gets another gig out it.

The point L1011 made is also excellent…the new rolling stock with be BEMU. Just take the catenary down section by section if it's in the way!

In order to drive in the sheetpiles and excavate the embankment, the machinery will have to operate from the rails which obviously has limitations with cables and supports above, regardless of whether they are live or not. Removing excavated material will also have to be done with rail wagons. Doing that both sides for 1.5km will take a long time, far longer than acceptable for closing the line. Doing it in sections doesn't help, any section still blocks at least one track between the two nearest sets of points, you might be able to divert some services onto the other track (assuming that can operate) but that would still seriously curtail services for the duration of the works or any section thereof.

You'd likely have to take out more than half the embankment for much of the length. There will be a certain distance from the rail line to be maintained, assuming some of the works can happen to the side while the railway continues to operate (I don't know which body will decide if rail services can operate alongside such works and if so, how much separation is required). Even with minimal separation, you need space for the tracks, any additional working space requirements above that needed for the tracks, plus the footprint of the retaining walls and its foundation. That will fairly eat into the embankment.

Like I said, I don't want to get into a discussion on it (not least because it is off-topic) but people here are seriously underestimating the scale of work which would be required to quadtrack or the impact it would have on the rail line and that should be pointed out.

Not speaking as an engineer, but I have to agree. This hardly needs to be the greatest engineering feat that humanity (let alone Ireland) has ever achieved.

It's not as if there are apartment blocks along right along the length of the steep enhancement. There are other sections that will be more challenging in terms of minimizing CPO/demolition.