The Dart underground project, shelved a decade ago following the economic crash, is being resurrected by the National Transport Authority (NTA), documents reveal. The â¬4.5 billion underground line to link Heuston Station to the Dart line by tunnelling under the city via St Stephenâs Green was one of the âbig threeâ transport projects planned during the boom, along with the Luas Cross City and the Metro. While the new Luas opened in December 2017, and a planning application for the Metro is due to be submitted to An Bord Pleanála shortly, the underground â by far the most expensive of the three projects at the time â was shelved in 2011.