|Type||Rapid transit, Heavy rail|
|Status||Under review (as of Sep 2017)|
|Locale||Dublin city centre|
|Planned opening||"After 2030"|
|Line length||7.6 km (4.7 mi)|
|Number of tracks||2|
|Track gauge||1,600 mm (5 ft 3 in) Irish gauge|
|Electrification||1500 V DC Overhead catenary|
DART Underground (Irish: DART Faoi Thalamh), previously known as the Interconnector, was to be a railway tunnel that was proposed to run under the city centre of Dublin, Ireland. The plans for the tunnel also included an expansion of the electrified DART and the Dublin Suburban Rail network, as well as a tunnel between Heuston Station and Pearse Station. For many years it was touted as 'essential' in order to integrate suburban services in the city, and to increase capacity on the rail system. It had been planned to leave the existing lines via the Phoenix Park tunnel and the Royal Canal idle in the event of the scheme being built , despite those lines already connecting Heuston Station with Dublin's Docklands - which the DART Underground scheme was supposed to achieve. Accordingly, when the Irish Government published the new national spatial strategy in 2018, the revised plans effectively dropped the scheme in favour of using the existing lines instead.
Having previously secured planning consent , the project was initially deferred in November 2011 until at least 2016, and by September 2015, it was announced that the project was to be redrafted to a lower cost design. In October 2016, a "scaled down" plan was published with a target commencement date (subject to railway orders and planning permission) "in 2020". As of September 2017, project planners suggested that it would be "[after] 2030 before passengers could use the new line". During 2017, the National Transport Authority reviewed the project, so as to identify cost saving measures (from the original €4 to €4.5 billion estimate), with the review expected to be "finished around the new year ".
DART Underground was first proposed in 1972 in the "Transportation in Dublin" study conducted by An Foras Forbartha, an anteceding body to Forfás (sometimes erroneously referred to as the 'Dublin Transportation Study') as an underground rail link to connect the 3 main Dublin Railway Stations.
Phase 1 Upgrade and electrify Howth – Bray (completed 1984 as the DART).
Phase 2 An Underground line from Connolly to Heuston. Rapid Transit tracks Heuston to Clondalkin overground. Spur to Tallaght from Clondalkin (a small part was completed in 2010 when Rapid Transit tracks were installed either side of Clondalkin)
Phase 3 A short northerly spur off the Maynooth line to Blanchardstown and a short southerly spur to Broadstone. (The former was never completed but was partly revived in 2001 as Metro West before that was itself shelved in 2011 and the latter spur was opened as Luas Cross City in December 2017.)
Phase 4 An underground tunnel from Broadstone to Sandymount. (This was later redesigned as Metro North from Drumcondra to St Stephen's Green and shelved indefinitely in 2011.)
The DRRTS, if completed as envisaged in 1975, would have resulted in a cross shaped pair of tunnels in the city centre meeting at a central station in Temple Bar.
The plan was next proposed in 2001 as an 'Interconnector' in the Platform For Change strategy report issued by the now defunct Dublin Transportation Office or DTO.
A Railway Order permitting the construction of the project was granted in December 2011 by An Bord Pleanála. In August 2014, Minister for Transport Paschal Donohoe TD was told that both the Dart Underground and Metro North projects would have had to rely on private funding if they were to be built. In 2010, the estimated projected cost for DART Underground was €4 billion, more than half of which was expected to be provided by a public private partnership arrangement. Mr Donohoe was told he had to decide on whether to proceed with DART Underground by 24 September 2015 when the Railway Order giving authority and planning approval expires. A High Court ruling reduced the period for which compulsory purchase order notices could be issued from seven years to 18 months. The NTA's Greater Dublin Area draft Transport Strategy 2016 – 2035 published in October 2015, expressed the desire to see the tunnel completed as part of the over all DART extension programme.
Delays and status
On 30 June 2010, Iarnród Éireann submitted an application to An Bord Pleanála for a Railway Order for the scheme under the Transport (Railway Infrastructure) Act 2001. Under this Act, the Board charged with considering planning, environmental and property issues regarding proposed developments.
A month later, in December 2011, in the Railway Order was granted for the development. The granting of the Railway Order permitted both the construction of the scheme and any necessary compulsory acquisition of property. It did not however commit funding to the project.
In September 2015, it was announced that the project had been cancelled in favour of a simpler alternative. However, it was planned to return as part of a future DART Expansion Programme, starting no earlier than at least 2020 or 2021.
As of 2016, the National Transport Authority was reviewing the DART Underground project, with a view to examining the design of the tunnels, and undertaking feasibility studies to see if it would be possible to use single-bore tunneling as opposed to twin-bore tunneling.
In September 2017, it was suggested that this review would complete early in 2018, and that -depending on the outcome of the review- works on the project would not commence until at least 2020. Revised projections suggested that it would be at least "2030 before passengers could use the new line".
There was considerable opposition to the project in Dublin's East Wall area where the tunnel would have begun and where tunnelling operations were planned to be located. People also complained that while they would have had to endure the disturbance created by the tunnelling works, they would not gain anything from the project as they would not have easy access to a DART station since they were roughly halfway between the Clontarf Road and Docklands stations. Iarnród Éireann responded, claiming that they can use Clontarf Road Station. It is a roughly 20 minute walk from East Wall to Clontarf Road station. 
In late 2017, developers expressed concern that planned developments near Pearse Street Station were declined permission on the basis of their potential impact on the proposed DART Underground project.
Dublin's existing DART line runs in a north-south along the Eastern seaboard from Malahide and Howth to the North of the city to Bray and Greystones to the south of the city in County Wicklow. The line passes through the city centre by means of the elevated Loopline Bridge across the River Liffey between Connolly and Pearse stations passing the elevated Tara Street Station on the South bank of the river Liffey.
If DART Underground were to be completed as proposed, the single-line DART would be replaced by two DART lines forming a rough X and intersecting at Pearse Station. The first line would begin in to the north-east of the city in Howth/Malahide following the existing DART line to Clontarf Road and then diverge eastward into a tunnel and to a proposed new underground station in the Docklands and then westward to a new underground station near Pearse Station, under St Stephen's Green (where it might interconnect with the proposed Metro North), Christchurch, and directly beneath Heuston Station. Emerging from the tunnel the line would then continue to a new overground station at Inchicore after which it would follow the existing South Western Commuter line to Hazelhatch to the west of the city.
A second DART line would follow the existing southern DART line from Bray/Greystones to Connolly Station, from which it would diverge on the existing but un-electrified line from Connolly to Maynooth to the northwest of the city in County Kildare with a branch off the line at Clonsilla to M3 Parkway, County Meath.
- Daniel McConnell (22 September 2015). "€3bn DART underground project scrapped in favour of scaled down version". Irish Independent. Retrieved 22 September 2015.
- "'We won't let go': Irish Rail is convinced the long-delayed Dart Underground will go ahead". TheJournal. 21 September 2017.
- "DART UNDERGROUND: Property Protection Scheme / DART FAOI THALAMH: Scéim Chosanta Maoine" (PDF). Irishrail.ie. Irish Rail. Retrieved 5 February 2018.
- "Metro, DART projects put off in plan". RTÉ News. 10 November 2011. Archived from the original on 12 November 2011. Retrieved 10 November 2011.
- "Dart Underground plan scaled down to slash costs". Irish Independent. 31 October 2016.
- Environmental Impact Study Dart Underground 2010 History of Archived 7 September 2013 at the Wayback Machine.
- Platform For Change Summary Report November 2001 Archived 19 November 2007 at the Wayback Machine.
- McGee, Harry (13 August 2014). "Dublin rail projects to rely on private funding". The Irish Times. Retrieved 29 September 2014.
- Iarnród Éireann. "About Us – DART Underground". Archived from the original on 3 March 2015. Retrieved 1 March 2015.
- Department of Public Expenditure and Reform (November 2011). "Infrastructure and Capital Investment 2012–16: Medium Term Exchequer Framework" (PDF). Retrieved 11 January 2012.
- "Railway Order granted for DART Underground". An Bord Pleanála. Retrieved 17 December 2011.
- "DART Expansion Programme". Archived from the original on 12 April 2016. Retrieved 2016-10-16.
- "Angry residents oppose DART Underground plan". Dublin People. 26 August 2010. Retrieved 23 February 2013.
- "Dart site office block decision unreasonable, says developer". The Times. 3 January 2018.