Just to play Devil's Advocate here, but being from Ballymun myself and talkling to my relations who still live there, it would seem there is woeful ignorance about what an elevated rail metro will look like and many community community spokespeople, and even the likes of Rosin Shorthall seem very eager to contunually hype-up the idea that MetroNorth is to be built on Easternders-style railway viaduct with sheds and lock-ups beneath, or dirty, dark alcoves.
I understand 100% percent why Ballymun folk are so negative about this because they are comparing them to the sheds and garages which are at the bottom of the 8 and 4 story blocks and were for decades perhaps the number one reason for so much anti-social issues in Ballymun. They were pretty horrific and a magnet for all manner of lowlife. This unfortunately is what people in Ballymun think the elevated section of the metro is going to be like.
When I explained to my relatives it is going to look something more like this.
http://www.subways.net/australia/brisbane.jpg
And there will be no issue with looking in people's bedroom window because the tracks will be lined with screens, their whole atitude towards an elevated section though Ballymun changes. The most common comments I got back was. "well that fair enough then, not like what I was thinking it was going to be like at all"
So I personally think the issue here is the RPA need to get up to Ballymun and explain to the people there what the viaduct/piers will actually look like with nice illustations and models. And show best practice versions in other residential neighbourhoods around the world. I bet the whole issue would be resolved very quickly and people would forget about extra tunnelling under Balymun.
If the RPA guys are reading this, then lads give it a go. People in Balymun are not objecting for the sake of it and if you explain to them properly what you're planning they will accept it.