Thread by @gavreilly

THREAD: So, about the Metrolink, lines being "dug up" (hint: no they're not) and four year disruptions being ruled out before they're even touted…

1/ So, firstly: Remember how we all tutted and scoffed at ourselves when we built two Luas lines that didn't connect – and couldn't, because the two tracks were built at different widths?

There was a reason for all that.

2/ This was because even before construction, the idea was that the Luas' green line would some day be incorporated into a full Metro line.

(What's the difference? Longer carriages, angles of turns, and strength of foundations.) irishtimes.com/news/luas-line…

3/ After the Luas, plans were published for an underground 'Metro North' project, providing a direct rail ink from Swords, via the airport, to the southside city centre.

But why stop there when there's already a Metro-grade line running south from there? Why not link them?

4/ The NTA's Greater Dublin Area Transport Strategy 2016-2035 proposes to do just this. It recognised that, especially once the Luas green line had extended to Broombridge, the extra demand would quickly lead to capacity problems.

5/ The Metrolink project, as originally published in May 2018, intends to address this.

It took the old Metro North plans and extended them, building an underground line from Swords to Charlemont and then taking over the existing Luas line southbound from there to Sandyford.

6/ (Yes, *take over* the line: the Luas line from Ranelagh to Sandyford becomes the Metro line.

From Sandyford to Cherrywood remains a Luas; the Luas Cross City from Charlemont to Broombridge remains a separate line of its own.)

7/ Obviously this requires a new 'fork' to be built in the track between Charlemont and Ranelagh, diverting the existing Luas into the new Metro tunnel. This inherently causes some disruption to the present Luas service.

This is true of ANY upgrade-the-Luas-to-Metro proposal.

8/ Upgrading the Luas to Metro also means having to extend some train platforms, which is easy in some places and slightly more challenging in others.

Where the plan gets complicated is where the existing Luas crosses over a road. A Metro track is simply too busy to drive over.

9/ There's only two cases where this happens, at the Stillorgan and Beechwood stops. The road at Stillorgan is indispensable (it serves the Sandyford industrial areas) so the track will be elevated onto a new bridge.

THIS is the closest the existing Luas comes to being "dug up".

10/ At Beechwood, the plan is simply to close the junction where the line crosses Dunhille Avenue. It's a relatively minor road, but residents and local reps have myriad complaints (diverted car traffic, lengthy detours, noise disruption, property price impact, etc).

11/ This is something the residents are apoplectic about. They say it will carve their community in two, and add a 1.5km detour to a trip between either end of the road. There's also fears about the price of local property prices, given the perceived disruption of a rail service.

12/ But what else do you do? The only way to build the Metro, but not close that road, is to keep the Metro underground for longer.

This means less of the existing Luas gets the upgrade it needs, and more duplication between old Luas and new Metro.

13/ That's a plan which is being teased out by the NTA/TII at the moment, leading to as-yet-unpublished proposals which would purportedly disrupt the Luas "for up to four years" (independent.ie/irish-news/new…).

It has not been stated exactly WHY this would mean a four-year disruption.

14/ It is difficult to see exactly what proposal could mean a disruption of so long anyway.

As already mentioned: aside from station upgrades, the main overground works are building the 'fork' to allow the Metro run onto the metro-grade existing Luas line.

15/ Of course nobody wants a four-year disruption (if indeed that IS the case at all) - especially now the line serves such faraway areas. That's why Shane Ross ruled it out today.

The policy question that poses: is that worse than closing off one road just south of Ranelagh?

16/ The likely outcome is that, faced with either closing Dunville Avenue or more extensive and expensive works leading further south, neither will happen.

The southern part of Metrolink will probably end up being shelved, and only Metro North will go ahead for the time being.

17/ This isn't quite easy either. If the Metro ends at St Stephen's Green (for example) and you don't build a giant underground depot, you need extra space that allows carriages to switch directions. Not exactly simple in a capital city centre.

18/ The whole premise of Metrolink is in the title: it's linking a Metro into something that's already there. The whole design is predicated on access to existing overground depots and facilities that were future-proofed for this purpose two decades ago.

19/ But, because one road in Ranelagh is sacrosanct and nobody can decide exactly which leafy southside Dublin area should have to put up with the building works, none of them will get the extra rail capacity the whole system will soon urgently need.

~fin~