The Government has announced that work will begin on Dublin's new Metro North rail line in 2021 and is due to open six years later.
The long-awaited link up between Swords and the city centre is part of a €7.5bn investment programme.
Finance Minister Paschal Donohoe says it is worth the money.
“If we don’t have a transport link to there, the potential to build homes, the potential to develop DCU, for example, will be capped, because this planning permission,” he said.
“This panning permission will not be delivered because the capacity will not be there to get people in and out of their homes and in and out of work.”
Mark Gleeson from Rail Users Ireland has welcomed the news, but fears costs could spiral.
"The figures depend on what the cost of the actual final plan is going to be,
"There are variable costs in terms of land, the price of land is increasing rapidly at the moment in Dublin,
"And also previous plans … may not be valid, as land that was required for Metro North may have been built on."