Iarnród Éireann is today lodging its application to build Dublin's underground DART interconnector which is designed to link up the city's transportation system.
The Government has consistently said that the underground DART and Metro North will both go ahead despite a combined cost of around €5 billion.
The application to An Bord Pleanála for the underground DART comes as the board prepares to give its decision by the end of next month on Metro North, which will run from the city centre to Swords.
The underground DART, or interconnector, has been described as the most important part of Transport 21. Running from the Docklands to Heuston Station and Inchicore it will allow rail passengers from Cork to connect to Belfast.
It will open up two DART lines - one running from Balbriggan to Kildare and the other from Maynooth to Bray, intersecting at Pearse Street station.
The underground DART will also link with Metro North at St Stephen's Green, with the Inter city lines at Heuston and with the LUAS.
Like the Metro North, the project will be a public private partnership and the Government will not have to pay for its construction until it is completed as planned in 2018 .
The Dublin Chamber of Commerce has called on the Government to publicly commit itself financially to the project's completion.
