DART underground - options

Sydney maybe, but not Melbourne. Melbourne has the world’s largest tram network (250 km of double tracks), plus a good regional rail network and a pretty decent bus service too. Rail has always been part of Melbourne’s development, and this has done a good job of keeping densities high. Houses in Melbourne suburbs might be a bit bigger than Irish ones, but the sites tend to be the same size or smaller, even in the outermost suburbs. Sydney has much more “American” suburbs, with large lots.

Munich’s driver-operated S-Bahn tunnel carries 29 trains per hour in each direction (2 minutes spacing, with a 2-minute empty slot) during peak periods using 1990s signalling and no platform doors. This is probably the limit of what you can do with non-automated heavy rail.

Mixing of train types on the same line is what keeps frequencies down on DART. Once you dedicate the tracks to the same model of train (or models with very similar acceleration/deceleration curves), you can really reduce lead times.

A two minute headway should easily be possible on a new-build tunnel using modern fast-accelerating trains and ETCS signalling. Actually, I’d expect the new DART+ Hazelhatch-Heuston section to be capable of this from start of service, but I doubt it will ever be timetabled like that.

I've previously on this thread suggested the same, basically a station where the platforms run from the corner of D'olier to Tara Street, straight run up for lifts, escalators etc to Tara, direct exit at D'olier and an underpass/corridor exit to College Green

Sure, and thats one of the reasons Metrolink was chosen instead, because the O'Connell Bridge station was judged to be horrendously expensive.

Choosing College Green for a station on DU doesn't have much merit when Pearse and Tara St are right there with much better connectivity. It's a poor value prop

What are the barriers to fully automating any heavy rail line really? The Dart South line seems to be the primary challenge due to thorny level crossings, but what other barriers exist that aren't a case of stuff like upgrading signalling etc?

Long Term the plans we have between AIRR and Fournorth etc will almost if not fully separate "commuter" (including DART) from "Intercity":

• D+ SW
• Fournorth
• Fast lines to Drogheda
• Fast lines to Portarlington
• Sligo/Heuston connector
• Redirecting Wexford trains via Waterford on improved lines

That leaves you with basically people commuting from North of Wexford to Greystones as the only 'Non-DART' commuter rail (if you presume that DART-esque service gets extended to Portarlington when the Fast lines are built)

If its only level crossings and signalling then that's "Just work" rather than anything insurmountable. Even if the service pattern for the outer reaches is far less heavy, if they all integrate and are automated then you can gain all the headway advantages etc and they just "slot in" to the timetabling.

I will say triangle transfers are fairly useful to have, biting the bullet on SSG for DU/Metro, GCD for DU/DART South, Tara for Dart South/Metro does spread the load quite well.

In an 'Ignore Spencer Dock, surface near Fairview' scenario, could GCD be reached and still curve nicely to avoid slowing trains?

General DART discussions have brought up that GCD is underutilised and could become a terminating station for non DARTs to simplify the core.

Adding DU connectivity and improving accesses there gives you a major 'South Docklands' growth focus while maintaining the 'close to the city' SSG stop that also can have you at Tara/O'Connell in a few minutes by swapping to Metro.

I think for Pearse I'm in no way opposed personally, but I think I would again site it (if we are still doing SSG) so that it can serve double duty as much as possible

While that's 350metres distance I would site the platforms in the centre of that space, with access points a 75m walk away at Pearse and the Liffey (or maybe a little closer on Pearse end and further on the Liffey end) that space can be used to do crowd management for the transfer and on the Liffey end captures:

• IFSC right across the bridge
• 9 minute Walk to Connolly for Intercity
• 7 min walk to George's Dock luas towards Spencer Dock Station
• 14 min walk to Spencer Dock itself

I still would not be upset if the powers that be pursued a 'project split' of sorts and regurgitated previous tunnel plans but only to go as far as St. Stephen's Green (or even Christchurch) as a Hueston 'line extension'. The stated default for any potential future further other extension phases could then be as per the route from the 2011 Railway Order (or nearest of the 2021 review if really needed to state it).

It would be nice if this could be done for the mid-2030s rather than wait to stated post 2042 to start looking at it again.

At least then the south city centre could get a couple of new rail stations, including to the existing less well served Christchurch (and the other planned DART station for Inchicore locals) and link to the north/south LUAS Green line… and Metrolink if it happens hopefully, as a direct heavy link to Heuston Station and the rest of the country.

All of the previous tunnel iterations went as far as Christchurch/ High Street, and 3 of the 5 short-listed line options in the 2021 review went past St. Stephens Green. It would take a few years to plan and tunnel to Christchurch or St. Stephens Green anyway and in that time a decision could be made on going further?!

Cost Benefit Analysis e.g. in the 2021 report did say best to not stop on the south side of the Liffey and to instead cross it and link to the rails on the other side of the city but, waiting for the full-blown version sometime in the far future (well past 2042) seem personally to me, less attractive.

This is especially if in the hopefully not so far future there may be four-tracking of the northern line, and an airport heavy rail line, to also consider to link into for 'future phases' of such a tunnel.

The M50 is a major problem if you want to surface at Fairview depot: you can't go over it, and if you go under you can't get back up to the surface in time. The only viable options are either the docks, or further north.

There is space to grade separate the lines at the Docklands if the joining point is brought south, but it requires either a slightly tighter curve on the line emerging from the tunnel, or a different orientation of the deep Spencer Dock station.. moving it east as you suggest would help. Currently both sets of tracks are elevated here as they approach the bridge (roughly 6m elevation), so it is an "at grade" join, but that will not be the case when one pair of tracks is climbing out of a tunnel. The biggest challenge is gradient, but I think it's doable if you can rise at 3% within the tunnel, before reverting to a more reasonable 2.5% once out.

If the underground line is still tunnelled as two bores as was planned, there's a lot more flexibility around exit points.

Wouldn't you then be:

• Surfacing on a curve
• Steeply rising on a curve to bridge the Tolka
• Be trying to tie in to the middle of the junction between to sections of track, as it crosses the Tolka?