Metro North has been given the final go-ahead despite doubts about the future of the project.
The Rail Procurement Agency was given permission for a 16.5-km track from St Stephen's Green to Swords last October.
But An Bord Pleanála had shortened the proposed route and asked that the rail depot be moved from Belinstown north of Swords to Dardistown south of Dublin Airport.
Today the board approved revised plans that would also involve permission for acquisition of lands.
Two plots are occupied by sports clubs Na Fianna and Whitehall Rangers.
There is also land owned by Fingal County Council used as an aircraft viewing area and land belonging to the Dublin Airport Authority.
The permission will last for ten years meaning these lands and others along the route cannot be developed by anyone else in the meantime.
It has been reported that Minister for Transport Leo Varadkar will announce before the end of the year the postponement of both Metro North and the Underground DART. The combined cost of which is estimated at €5bn.
But the Rail Procurement Agency is reported to have already spent €200m on the Metro project and is due to select a winning bid to build and operate Metro North from two competing consortiums Celtic Metro and Metro Express.
It is also understood the bidders could be entitled to compensation if the project is deferred.
Mr Varadkar recently announced that the Metro West project would not be going through the planning process.