However traffic volumes have been falling along the route in recent years partly due to the economic downturn end of the boom, but also mainly due to the fact that many quarries along the route are nearing the end of their productive lives.

Changed to emphasise the non-temporary nature of this volume drop.

The motorway proposal is seems a hangover from the Celtic Tiger era when there seemed to be no limits to public spending or population, economic and traffic growth, oil was plentiful and cheap, and carbon footprints were almost unheard of.

Sharpened the focus on the fact that the justification is no longer there (I am not sure we want to associate the later years of the Celtic Tiger with "unlimited public spending"). Also, you cannot prove that the proposal is a holdover from the previous economic era - but you can prove that it sure looks that way.

It is being perpetuated by road planners who need to justify their existence but have simply run out of viable new motorway projects to pursue.

I would think very hard about whether I would want to make this accusation. If the point is simply to emphasise bureaucratic inertia, there are ways to phrase it that will not rub the people who make the decision you want to influence quite as much the wrong way.

Why are we wasting spending money on planning such crazy developments an entirely new road, and ignoring when overhauling the existing infrastructure is much simpler, more cost effective, and less environmentally destructive alternatives? It is time our planning systems took account of our changed economic circumstances and started planning for a more sustainable and lower carbon emissions future.

And [I]f we do want to dramatically improve our public transport infrastructure, an extension of the Luas beyond Saggart to the Naas/Blessington area would be a good start.  After all Blessington did have its own tram service until 1932.

Toned down the accusations, emphasised the technical and logistic superiority of your alternative proposal.

- Jake

If you only spend 20 minutes of the rest of your life on economics, go spend them here.