It is claimed plans for Dublin's Metro North have been revised with the hopes they will unlock large tracts of land for housing.
The Irish Times reports the latest version would see the line running underground to as far north as Santry.
Meanwhile, there are concerns DART underground will not get funding in the Government's National Planning Framework, despite being committed to in the Greater Dublin Area strategy.
Mark Canavan from the Dublin Chamber of Commerce says the whole country would benefit from it.
He said: "It's main behefit would be to connect the central business district around the docklands and the city centre with high-density areas in the suburbs, and just provide easy access around the city.
"So, it would take an awful lot of cars out of the city. Its main benefit would be to connect the four rail lines which are currently aren't connected, so it would be a benefit to someone travelling to Cork from the airport."