The first was a north–south line which would run from Swords to Shanganagh via Dublin Airport, Finglas, Broadstone, the city centre, Ranelagh, Sandyford and Cherrywood.

It was described by Transport Infrastructure Ireland as "an important commuter link for the communities and institutions of North Dublin City and County".

[17] It was speculated by the media that the Metro North Project would be indefinitely deferred on 12 August 2011 following a review by Leo Varadkar, then Minister for Transport, Tourism and Sport.

[19] In September 2021, government representatives indicated that the 2027 target would not be met and "was never likely to be achievable",[6] with some reports projecting that construction would not commence before 2027.

[3] On 22 March 2018, the National Transport Authority announced revised proposals for the former Metro North railway line, now called 'MetroLink'.

In addition the route was changed to provide an interchange with existing DART services at Tara Street station in the centre of the city.

The tunnel construction method was changed from twin-bore to single bore to minimise disruption and reduce costs.

MetroLink is to be driverless and the stations are to incorporate platform screen doors, while MetroNorth was designed to be manually operated by drivers using line-of-sight.

By developing in two phases the closure of the Green Line could be reduced and more time given to upgrading the existing pedestrian crossings to be fully grade separated through the use of underpasses.

[29] Engineering consultant firm SNC-Lavalin was appointed by Transport Infrastructure Ireland in March 2020 as operations advisor for the project.

[31] As of April 2023, a number of bodies (including Irish Rail, Dublin Airport, Abbey Theatre and Mater Hospital) raised concerns about aspects of the proposals outlined in the planning application.

[30] According to an initial planning report, the metro is proposed to operate for 19 hours per day, with services every 3 minutes at peak times.

[4] As of March 2021, the Minister for Public Expenditure and Reform Michael McGrath reportedly "warned that existing budgets may not cover" the full costs of MetroLink and related projects.

[38] In March 2019, the revised plans were released with the intention to upgrade the Green Line after the northern section is operational.

Planning on the Metro West Project was suspended in September 2011 following a review by Leo Varadkar, then Minister for Transport, Tourism and Sport, as money to construct the new railway would not be available in the foreseeable future.

[42] Metro West plans, published in 2007, proposed lines which would run overground, with some tunnels and bridges to avoid major road junctions.

When developing options for Metro West, the Railway Procurement Agency (RPA) considered routes south of the M50, serving Finglas more directly.

[45] On 11 November 2008, the RPA chose their preferred route for Metro West, including indicative stops, depot and Park and Ride locations.