Electrification of Dublin commuter rail services to Kildare, Maynooth and Drogheda, and on the first phase of a reopened Navan line, was proposed to the Government in July 2004 by Iarnród Éireann, according to documents obtained by The Irish Times.
Released under the Freedom of Information Act, the business case for a Greater Dublin Area Integrated Rail Network also included the crucial rail interconnector between Heuston Station and Spencer Dock, which was estimated to cost €1.3 billion at 2002 prices.
Although all monetary figures in the documents were meticulously blacked out by the Department of Transport, it was possible to discern that the overall cost of the investment programme - which also included Dart upgrades - was put at €3.4 billion.
"Immediate priorities" included quadrupling the Kildare line as far as Adamstown, four new stations along the line as well as new stations at Spencer Dock, Phoenix Park, Pelletstown and Porterstown, and reopening the disused Navan line to Pace, north of Dunboyne.
The investment programme also included a Dart spur from the northern commuter line to serve Dublin airport, although it was clear that if the Government opted for a metro line linking Swords with St Stephen's Green, this would become a redundant proposal.
In the longer term, having completed resignalling in the city-centre to relieve the "Connolly bottleneck", Iarnród Éireann sought approval to electrify the lines serving Kildare, Maynooth and Drogheda and to build the interconnector between Heuston and Spencer Dock.
This would include five underground stations: at Heuston (linking with the Tallaght Luas line); Thomas Street (serving the Digital Hub); St Stephen's Green (linking with the Sandyford Luas line and the Swords metro); Pearse Station (linking with the Dart); and Spencer Dock.
According to Iarnród Éireann, the investment programme would result in a four-fold increase in peak rail patronage by 2016, superior access to Dublin city-centre from nearly all population centres within a 100km commuter belt and convenient integration of all rail services.
Endorsed by Goodbody Economic Consultants, who said that the overall thrust of the plan "makes operational and market sense", funding options included additional exchequer grants, borrowings, leasing and public-private partnership arrangements and levies on commercial and residential schemes.
Areas with commercial development potential included Docklands, the Digital Hub, the Guinness brewery site, Heuston and Inchicore Works, while those with housing development potential were Docklands, Inchicore Works, west and north-west Dublin and south Meath.
In its evaluation of the plan Goodbody said that since all trains going through the tunnel between Heuston and Spencer Dock would have to be electric, "a decision needs to be taken with regard to whether all future purchases of rolling stock will be electric- powered".
The Department of Finance expressed concern that the €1.3 billion cost of the 5km rail tunnel could be underestimated by some €500 million in 2004 prices "if the general contingency figure was increased to metro levels". Moreover, it noted, this would need to be revised upwards.
In June, Iarnród Éireann conceded that the interconnector would cost "significantly more" than the 2002 estimate of €1.3 billion.
This was also based on a single-bore tunnel, probably with a fireproof wall between the two tracks to meet railway safety concerns.
Under Transport 21, which former minister for transport Martin Cullen has described as "my brainchild", the Swords metro line is to be up and running in 2010 although the more strategically important rail tunnel between Heuston and Spencer Dock is not due for completion until 2015.
