The government is going to spend 150 million euro on 41 new train carriages aimed at reducing congestion for commuters around the Greater Dublin Area.
It comes after Irish Rail said it might have to make some services "pre-book only" because of overcrowding.
Transport Minister Shane Ross says today's announcement will boost train capacity by a third by 2021.
Meanwhile Irish Rail plans to buy 600 trains over the next decade, first to replace the ageing Dart fleet and then to provide intercity services.
But it's said the first trains delivered could be hybrids, just in case key routes can't be electrified before 2024.