A new DART depot west of Maynooth station was not approved due to flood risk concerns.
An Bord Pleanála has approved the DART+ West project, extending the DART network from Connolly/Spencer Dock in Dublin to Maynooth and on to the M3 Parkway near Dunboyne.
The project aims to provide sustainable transport options for communities like Maynooth, Leixlip, and Castleknock.
Iarnród Éireann applied for a Railway Order in July 2022, planning to start construction in 2024 and begin service by 2029.
The plans include a new station at Spencer Dock and a second entrance at Connolly Station.
A new DART depot west of Maynooth station, however, was not approved due to flood risk concerns.
Cllr Angela Feeney said the the decision to refuse permission for the Maynooth depot is "exceptionally disappointing".
"In the interests of rapid delivery of these essential projects for North Kildare, Irish Rail must both tender for the elements of the project which have been granted permission immediately; and must also commit to applying for a new Railway Order for the Maynooth depot at the first instance," she said.
She added: "It would be outrageous if a multi-year delay to this project is caused by what should be an easily amendable element of the planning process."
Mark Gleeson from Rail Users Ireland says Irish Rail has no more room in its existing infrastructure.
He said until a depot is provided in Maynooth, there will be no extra trains ordered to increase capacity and frequency not just on the Maynooth line but on the DART+ South West Route out towards Hazelhatch.

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