Failure to spell out the reasoning for Metro West undermines credibility of plan, writes Frank McDonald, Environment Editor.
On the long shopping list of projects in the Government's €34.4 billion Transport 21 investment programme, the biggest question mark hangs over Metro West, which would link Tallaght with Lucan, Clondalkin, Blanchardstown and Ballymun.
At present, there isn't even a bus service between these centres.
Now it is proposed to provide them with what the Railway Procurement Agency (RPA) calls a "modern, attractive and highly accessible urban railway", which would have a capacity of 30,000 passengers per hour.
According to Minister for Transport Martin Cullen, "preliminary forecasts suggest that Metro West . . . will carry up to 20 million passengers a year". Yet we have not been told what the basis for these "forecasts" is or how much it will cost to realise them.
As in the case of Metro North, which would link Swords and Dublin airport with St Stephen's Green, no business case or cost-benefit analysis has been published for Metro West. Indeed, like every other element of Transport 21, this project is shrouded in secrecy.
Even calling it a "metro" is a misnomer. As Mr Cullen himself noted yesterday, it would run entirely on the surface, even crossing road junctions in a similar manner to the Luas, although bridges would obviously be required at major roads, railways and other crossings.
In effect, Metro West would be a souped-up version of the Luas. Even the computer-generated image issued by the RPA shows a fatter-looking tram at a street stop. By contrast, much of Metro North would run underground - like most "metros" worthy of the name.
Yet Metro West is now going to public consultation, and the RPA intends to make a decision on which route it would follow "early in the new year". Detailed design work would follow, with a view to submitting an application for a railway order "within a year".
Curiously, the half-orbital rail line is not due for completion until 2014, which would make it one of the last projects to be delivered under the Transport 21 timetable. Why it could take so long is a mystery, but the delay is presumably related to its procurement under a public-private partnership.
As for why it's needed, the Minister said west Dublin "has seen some of the most intense growth in housing and other development in the last decades [ and] this has resulted in large demand for travel to and from and within the area".
He might have mentioned that the proliferation of shopping centres, business parks and industrial estates in the M50 corridor is largely responsible for chronic congestion on the motorway that was originally meant to serve as a by-pass of Dublin.
But while the pace of development in west Dublin and beyond has been intense, it could hardly be called intensive. It has all the characteristics of a North American "edge city", which means that there would be long distances to get to "metro" stops.
If the shortest of the two route options is chosen, the proposed rail line could offer shopping centre excursions between The Square in Tallaght, Clondalkin town centre, Liffey Valley shopping centre, Blanchardstown centre and Ballymun town centre.
The M50 has been dubbed by economist Colm McCarthy as "Dublin's new main street", and Metro West would reinforce the edge city axis. It would also connect with Metro North, the Kildare and Maynooth rail lines, the Tallaght Luas line and the proposed Lucan Luas line.
With Metro North due to be completed in 2012 at a likely cost of €3.5-€4 billion, who can say that a government more strapped for cash than the present one would not pull the plug on Metro West?