The big question about the M3 is whether it's needed at all. It is not one of the five motorways listed as a priority in the current National Development Plan (NDP). Nor is the greenfield dual carriageway that will replace the N2 between Finglas and the Rath roundabout, north of Ashbourne.
On the basis of these plans, we will end up with three major highways running northwards from the M50 in very close proximity to each other: the M1, which has already been completed as far as Dundalk; the new N2, which will include town by-passes, and the M3 from Clonee to Kells.
The M1, between the Dublin Airport interchange and Dundalk, opened in June 2003, costing €819 million. The latest estimate for the M3 is €800 million, including an allowance for archaeology. The first 17 kilometres of the new N2, currently under construction, will cost €207 million.
Nobody would deny there is serious congestion on the existing N2 and N3, mainly caused by commuters heading into Dublin. Ashbourne, Slane and Ardee are notorious bottlenecks on the N2, as is Dunshaughlin on the N3. These towns and villages should have been by-passed years ago.
That's what the National Roads Authority's Roads Needs Study proposed as part of wider plans to upgrade the N2 and N3 to dual carriageways. But this relatively modest 1998 study was supplanted in 1999 by the Government's NDP motorway programme, without a shred of evidence.
At present, the M1 is operating at about half of its capacity and could easily take diverted traffic from the N2 and N3. The best option would be a motorway link between the outskirts of Navan to the Drogheda by-pass on the M1, following the route of the railway line that carries ore from Tara Mines.
The rationale is simple. Minimal severance would be caused by such a plan, while the archaeological risks are likely to be a lot less serious than on the proposed route of the M3. In addition, the proposal would by-pass both Navan and Slane, though the latter would still need one of its own on the N2.
At present, the M1 is operating at less than half its design capacity north of the airport interchange. Giving traffic on the N2 and N3 the option of using it would make sense in itself, but it would also provide much-improved access to the growing port of Drogheda as well as to Dublin Airport and Dublin Port.
The suggested link road would also be much shorter (at 26km) than the two motorways and, therefore, much cheaper to build (at around €260 million).
Even allowing for the extra cost of by-passing Dunshaughlin, Ashbourne and Slane, it is obvious that the overall bill would be considerably lower.
What would happen then to the existing N2 and N3? Mainly two-lane with no hard shoulders, they could be retro-fitted as barrier-separated "2+1" roads, which would offer motorists the opportunity to overtake safely by using the alternating middle lane - as planned for parts of the N20 Cork-Limerick road.
Even if the N2 and N3 are replaced in whole or part by four-lane dual carriageways, the existing roads would almost certainly have to be given the "2+1" treatment on safety grounds alone. Experience in Sweden has shown that this has a dramatic impact in reducing head-on traffic accidents.
The possibility of linking the N2 and N3 with the M1 was examined in a 2001 study on the viability of an "outer orbital route" around Dublin. Though it found merit in the proposal, implementing it had to take into account "the limited availability of funding and the competing demands for this funding".
An imaginative proposal to build a single motorway to replace the N2 and N3, put forward in 2000 on behalf of the Bellinter Residents Association in Co Meath by retired civil engineer Alan Park, was rejected by the NRA on a number of grounds. But the real reason was that it was a radically new idea.
One of the ostensible reasons given was deeply ironic. A new motorway between the N2 and N3 would "run through a landscape currently undisturbed by major road infrastructure, with potentially serious implications for communities, the environment and farm severance". Not to mention archaeological sites.
Father Sean McDonagh, a Columban missionary and committed environmentalist, says even if the M3 goes ahead "all it would do is bring you to the bottleneck at the M50's Blanchardstown interchange 20 minutes earlier" rather than shortening overall commuting time. "It's just crazy."
Frank McDonald
A "march to save Tara" will be held in Dublin this afternoon, assembling at 2 p.m. outside the Garden of Remembrance, Parnell Square. Organised by the Save the Tara/Skryne Valley campaign, it will end with a rally at Wood Quay, site of earlier protests over the destruction of archaeological remains.