A planning application for a major transport project in Dublin is due to be submitted to An Bord Pleanála (Irish Planning Board) in September.
Irish Department of Transport said the MetroLink project would “transform public transport in Dublin and improve interconnectivity with national rail links”.
It is expected to enter into operation in early 2030.
Transport Secretary Eamon Ryan said he was confident the project could be delivered on time and on budget.
He added that the €9.5bn (£8.16bn) cost estimates were “overly cautious and conservative”.
Mr Ryan described the MetroLink plan as a “mega project” which he said would transform public transport in Dublin.
The project aims to connect the north and south of the city.
It will be 19.4km long with 16 stations, mostly underground, running from the north of Swords to Charlemont Street in the south of Dublin city centre.
The department said there will be trains running every three minutes during peak hours, capable of carrying up to 20,000 passengers per hour in each direction.
It will interchange with the DART (Dublin train service) and Luas (tram service) transport systems.
By 2050, the Irish government estimates it will provide more than one billion carbon neutral fully electrified passenger journeys.
A planning application will be submitted in September, with the Department for Transport recommending its approval.
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