Ireland’s national rail operator Iarnród Éireann will seek planning permission early next year to build an underground railway in capital city Dublin to connect the existing rail lines.

The estimated €3bn DART (Dublin Area Rapid Transit) project involves building a 7.5km subway to link the Luas network, Metro North, the Kildare line and the Northern rail system.

The planned line would run from Inchicore to the Docklands covering six new stations – five underground and one overground.

The line would include two tunnels, each 24m below ground level.

The subway is expected to carry 20 trains in each direction per hour, catering to nearly 64,000 commuters every hour.

The operator expects the work, if approved, to begin in 2011 and finish by 2016.