Rail chiefs today sought permission to press ahead with a €2.5bn Dart Underground in Dublin with work expected to begin within two years.
An application lodged with planning authorities maps out the proposed 7.6km twin tunnels to be bored under the city centre in an attempt to treble the number of rail passengers.
The project will connect the Northern and Kildare rail lines, with underground stations built at Spencer Dock, Pearse Station, St Stephen's Green, Christchurch and Heuston Station. A new overground station would also be built at Inchicore.
Transport minister Noel Dempsey refused to disclose how much funding the Government would have to contribute to the public-private partnership scheme.
The Government will apply to the European Investment Bank, which recently pledged €500m towards the Metro North project, for some of the financing.
Potential private backers have until July 20 to express an interest. Investors would take a share in profits under the plans.
"There has already been significant interest," Mr Dempsey's spokesman said.
Under the ambitious proposals, Dart Underground will link all of the capital's rail systems - Dart, Commuter, InterCity, Luas and Metro - to form for the first time a fully integrated rail network.
Iarnród Éireann believes the project could increase passengers three-fold to as many as 100 million journeys on the Greater Dublin rail system every year.
Mr Dempsey claimed the railway order application - the equivalent of planning permission for rail projects - was a major stepping stone towards a mass transit system for the city.
"Not only will this project connect Iarnród Éireann's routes it will also provide links with the Luas and Metro at St Stephens Green, Spencer Dock and Heuston stations," he said.
"It will also provide for new stations at Inchicore and Christchurch, thus opening up new areas for travel by train."
The plans are being submitted under the Government's Transport 21 investment programme.
The work involves building 8.6km of new railway - 7.6km of which will be in tunnels - from the CIE Inchicore Works to tie into the Northern mainline, south of East Wall Road and north of the Docklands area.
Iarnród Éireann said construction, involving two boring machines tunnelling under the city at an average depth of 24 metres, would be completed and the system up and running by 2018.
Up to 7,000 jobs are to be created during construction and thousands more indirectly with improved access to retail, commercial, leisure and tourist destinations in the city, it is claimed.
Frequency and capacity on the Dart Northern, Maynooth and Kildare lines would be increased while the Dart would be extended to Maynooth, Hazelhatch/Celbridge and the Northern line.
Pearse Station will become a central transport hub connecting all lines.