* The planned 7.5km tunnel will link the Docklands with Heuston Station and terminate at Inchicore.
* It will allow passenger numbers on DART and commuter lines to treble from 33 million passengers at present to 100 million.
* It will cost €2bn to deliver and will be built under a Public-Private Partnership deal.
* It is due to open in 2015, the same year that Metro North is delivered.
* It will pave the way for two DART lines in the capital: one from Hazelhatch (Celbridge) to Bray, and the second from Maynooth to Howth.
* The stations are at the Docklands, Pearse Street, St Stephen's Green, Christchurch, Heuston and Inchicore.
* The system will link with Metro North, DART, commuter services, intercity and Luas.
* An estimated 6,000-7,000 construction jobs will be created during the building phase.
* Planning permission will be sought later this year, and it is hoped to begin work in 2011.