A planning application for the MetroLink transport project will be lodged with An Bord Pleanála in September, with an expectation that it could be in operation in the early 2030s.

The Minister for Transport said he had secured agreement from the Cabinet to proceed with the fully segregated railway for the capital.

Eamon Ryan described the MetroLink plan as a ''megaproject'', which he claimed would transform public transport in Dublin.

The project has big ambitions connecting the north and south city.

It will be 19.4km in length with 16 stations mostly underground, running from north of Swords to Charlemont Street in the south of Dublin City centre.

It is envisioned that MetroLink will be fully automated, with trains running every three minutes at peak time, capable of carrying up to 20,000 passengers per hour in each direction.

It will interchange with the DART and Luas transport systems.

The preferred route for new MetroLink according to its website

By 2050, the Government estimates that it will provide more than one billion carbon neutral fully electrified passenger trips.

A planning submission will be lodged in September, with the Department of Transport recommending its approval.

A final costing has not yet been worked out because the project still has to go through the planning and procurement stages.

Artist's impression of future MetroLink station at St Stephen's Green, Dublin

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However, early estimates for the transport plan comes in at €9.5bn, with the most extreme figure putting it at €23bn.

Three quarters of the cost during construction will be paid for by the Exchequer and the final quarter by a public private partnership.

Minister for Finance Paschal Donohoe told a media briefing a range of cost scenarios have been worked out, taking into account inflation pressures and changes to the economic environment.

The Government said it does not expect the figure to go as high as €23bn. The MetroLink statement quote a range of between €7.16bn and €12.25bn.

Minister Ryan said he expects the overall cost to come in at the lower range estimate of just over €7bn because "the tenders could be lower" to deliver the project.

He said it is not cheap to build transport projects in Ireland, but reiterated he is confident that it will deliver benefits to the Irish economy over time.

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MetroLink represents the largest ever proposed single capital project in Irish history, according to Minister for Public Expenditure Michael McGrath.

He added that when combined with BusConnects and DART+ it can "revolutionise" public transport.

National Transport Authority Chief Executive Anne Graham said that today was an important day for Irish public transport.

She said: "MetroLink is about providing a frequent, reliable, sustainable alternative as part of an integrated system, so that we can encourage more people to get out of their cars and on to public transport."

Transport Infrastructure Ireland Chief Executive Peter Walsh said the new service will have an "end-to-end journey time of only 25 minutes, as part of an integrated public transport system".

Sinn Féin spokesperson on Transport Darren O'Rourke welcomed the re-announcement of the long promised MetroLink, but has called on Minister Ryan to explain the ballooning cost.

He said: "This project has been on the cards for 20 years at this stage. Communities and commuters have waited far too long for this important rail link into the city.

"We need assurances that this project will now be finally delivered on budget and on time, and ahead of schedule if possible.

"I am concerned about the massive cost escalation for this project already.

"The original National Development Plan 2018-2027 estimated this would cost €3bn. Today, the Government are saying it could cost up to €12.25bn, over quadruple that previous estimate."

'Objections cannot be rules out'

The Chief Executive Officer of the National Transport Authority (NTA) has predicted that the MetroLink project will be delivered by 2034 and cost €9.5 billion. Anne Graham said that inflation and labour costs were included in the calculations made in the project.

Speaking on RTÉ's Drivetime she said international workers who specialise in tunnelling would be brought in to work on the project.

Ms Graham said that objections cannot be ruled out, but she had confidence that the public consultation that has taken place already has been worthwhile.

Meanwhile, business group Ibec said that MetroLink will contribute to the development of a more accessible, integrated, and efficient transport network in Dublin.

Aidan Sweeney, Ibec Dublin & Eastern Region spokesperson, said that Metrolink is needed for the development of an integrated and sustainable public transport network that will meet future demand in Dublin.

"As we transition to a net-zero society by 2050, a wholesale return to pre-Covid commuting patterns must be avoided. As it stands, Dublin is far too car dependent," Mr Sweeney said.

"Metrolink will offer a significant public transport option for people travelling between Dublin city centre and serving the growing population in Fingal and across north Dublin," he said.

"The new rail link offers improved quality of life for residents and workers through shorter commutes, better air quality, and more leisure time. People will also benefit from improved accessibility to Dublin Airport, which is attractive to tourists and supports the further enhancement of Dublin's experience economy," he added.