DART underground - options

While alternative connections are interesting, if it doesn't connect to the coastal line North of Connolly, then you haven't solved the Connolly/loop line bottleneck. And if you are not connecting to the Kildare line out of Hueston, you are wasting the 40km of the best proper fully grade-separated electrified rail alignment in the country by terminating services away from the centre in Heuston or sending the trains in a long loop bypassing most of the city centre.

The goal isn't a "better" London Overground type system (with out-of-centre terminals and alignments that avoid the city centre proper) - the only type of heavy-rail metro most people in Ireland have experienced it seems - where legacy heavy rail is used to provide some peripheral and orbital connectivity. The idea is to run Euro-style heavy-rail metro - pretty much indistinguishable from metro. Most recent city trip to Madrid was like this - heading to the centre of Madrid from the airport, half the trip used a "DART" and not a "metro" but I bet most Irish visitors will only extol Madrid's metro.

"Euro-style" heavy-rail metro systems (unlike say "London Overground" type systems) generally provide through-running, travel through the very centre of the city and run direct and efficient alignments. I just don't see any other interconnection, except that between the Kildare route (somewhere west of Heuston) and the northern coastal (somewhere north of Connolly) being all that useful if the goal is to provide proper metro services using heavy rail.

A future DU tunnel which connected Maynooth to GCD/Pearse, SSG, Christchurch, Heuston would be a fantastic alignment.

It wouldn't be as good as the classic X arrangement because many of the no-change journeys on such a line/service would offer very little utility - an example would be Leixlip to say Adamstown - which would be a 40km train ride to cover a 4km crow-flies distance. Relatively straight alignments provide more utility than ones that curve around or particularly are U shaped as all end-to-end trips provide utility.

One thing I've always felt uneasy about the X arrangement was that you were going to piss off lots of people living on the coastal route and get lots of push back on it.

Think of folks living on the south side who work at East Point or folks living in the north side, but working at various locations on the south side.

They go from having no change trip to a trip with a change and possibly 2 changes for those living in Howth!. That is going to lead to a lot of pissed off people. Many of whom choose where they live based on the DART line. 

This makes little sense to me but sadly I can well imagine the Irish Times running a campaign along these lines. Right down to using words like "folk" for passengers we are expected to have sympathy for.

It is same refrain we've heard over and over used to attack projects to improve PT Ireland - find a small number of existing customers who might have to change their travel patterns in some minor way and give them a soapbox to complain and vent. Ignore the huge benefits that would acrue to a much larger cohort.

It like that blind guy they found and used as a basis to bash BusConnects because this one person would now have an extra change. But absoultely no mention of the thousands or tens of thousands of users who would benefit.

These arguments are incomplete (and often disingenious) because they require ignoring or discounting to zero the utility provided to future users and usage patterns. In other words, look at the cost to existing passengers but ignore the benefits to future passengers (and existing ones who would benefit from the change).

For just one of your examples - passengers coming from coastal North. Are we really suggesting that a direct access to SSG (including Green Luas) and Christchurch is worth less utility than direct access to stations south of GCD? I feel confident in predicting that SSG would attract 10 times the patronage than any station South of GCD.

And this was a "I don't believe it but I'm just saying what others will say" type of post, then please spare me. If I want to read one-sided arguments about the costs PT projects, I can always pick up a copy of the Irish Times and get my fill there.

Yeah I might have been a bit strong but it touched a nerve as it echos much of "human interest" approaches taken by the press as a means to attack PT projects. "But someone will have to do something a bit differently!!"

I simply don't see the need to divert Northern Darts away from Loop Line.

Not sure I fully don't understand your position. You don't see a need for an interconnector at all or you think the intersecting U idea delivers more utility/value than the X type arrangement?

@loco_scolo - I think the intersecting U idea has merit as I believe the most important thing is to allow through-running of electrified commuter heavy rail services in the centre of the city and if the X configuration proved to be impossible or extremely expensive and/or disruptive it would be my second choice. The key purpose is to increase radial capacity and frequency. I'm not convinced (yet) that the X configuration is infeasible but I think the U configuration is a reasonable backup.

But I think your idea of heavy-rail extensions to Tallaght and the like are non-runners and miss the point of heavy-rail metro to some extent.

The idea of "interconnectors" as have been realised all over Europe was/is to exploit under existing/legacy heavy rail alignments which, because of the typical 19th century rail alignment configuration (terminal stations dotted around the periphery of the city cores), can not support decent metro-level of service because of the lack of through-running in the centre.

Heavy rail tunnels and new alignments in urban or even sub-urban areas are extremely expensive - particularly the stations as the platforms are huge requiring very expensive stations. Thus the classic European (and now British - with Crossrail in London) formation is to choose the shortest/least cost connecting tunnel that allows you to use existing alignments to support through-running metro-like frequencies.

Any brand-new urban rail alignments and tunnels which do NOT connect existing heavy rail lines at both ends, should be to metro/ML-type standards, not heavy rail - they are cheaper and easier to build and allow more flexibility in terms of curvatures and gradients and passengers prefer higher frequencies.

Thus I would NOT be in favour of heavy rail extensions in the city itself except for some sort of interconnector. I do think Tallaght needs a new/proper rail connection but I would serve it using an ML type system (say going to Coolock/Howth Junction on the other side).

If the core of the heavy rail system is sorted out (with an interconnector), then further heavy rail extensions should be at the outer periphery - like to Navan - where the costs are relatively low.