Disruptions from Maynooth and Dunboyne to Dublin can be expected.

The €10 billion project was given the green light last week, 25 years after it was first proposed, with operations set to begin in the mid-2030s.

It's now being projected that some busy western commuter lines to Dublin city centre will face major disruption for up to 21 months, as per the Irish Times.

Partial closures will be required on the Western Commuter Line and the South Western Commuter Line, from Maynooth and M3 Parkway near Dunboyne, to Connolly and Docklands, in order to facilitate construction at Glasnevin.

Niall Haverty, inspector for An Coimisiún Pleanála, stated in a report that there would be a 'significant negative impact' on the lines, but reassured the public that this would be outweighed by the long-term benefits.

The MetroLink is set to run mostly underground from Swords to Charlemont, serving 16 stations along its 18.8 kilometre line.

The service will interchange with Irish Rail services at Glasnevin and Tara Street.

At Glasnevin, existing tracks will be lowered by two metres, resulting in the closure of the western line through the area for almost two years.

Services coming from the M3 Parkway will be unable to continue to the Docklands and will have to terminate at Broombridge.

The South Western line will be affected for just five months; however, a longer section of the line will be impacted.

Trains from Maynooth to Connolly, as well as trains using the Phoenix Park Tunnel to reach Connolly, will terminate in Heuston.

Irish Rail stated in its MetroLink application that the closures would have a 'significant disruptive impact' on passenger, freight, and maintenance services, with Mr Haverty's report saying: “They contend that this closure period is excessive and that a shorter closure period should be feasible."

Furthermore, Irish Rail raised the issue of its Dart+ programme, which aims to electrify the lines and upgrade them to Dart-standard service frequencies, saying that these upgrades 'may be completed or under way prior to MetroLink construction commencing,' according to Mr Haverty.

Transport Infrastructure Ireland (TII) acknowledged the service disruptions and impacts on customers, but said this represents a 'worst-case impact' and confirmed it was working to reduce the overall impact of the closures.

Mr Haverty added that it was 'somewhat surprising' the two public transport bodies 'have not reached an agreed position in relation to the proposed Glasnevin Station' prior to submitting their applications.

“This is intended to be an interchange station between the MetroLink and the heavy rail network, and it would have been reasonable to expect that matters relating to how the interchange would be built and operated and the amount that the railway tracks would need to be lowered and would have been agreed, at least in principle, in advance of the applications being made," he said.

During the time of disruption 'any alternative transport arrangements required, with options within our own network, and with bus and Luas services' would be 'considered and determined, in consultation with the NTA'.