The Government has approved a timetable for extending DART services to Kildare and to Drogheda.
Minister for Transport Eamon Ryan said that when the project is complete the number of people living within 1km of a DART station will go from 250,000 to 600,000.
He said the announcement "highlights our commitment to invest in high-quality public transport and decarbonise Ireland's transport system. This rail project will transform the lives of people living in communities along the route, giving them a fast, reliable and frequent train service into Dublin "
DART + South West will see the line from Connolly station out to Celbridge electrified and a new low emission, high frequency train service to stations at Islandbridge, Park West and Cherry Orchard, Clondalkin, Adamstown, and Celbridge and Hazelhatch.
There will also be a new station at Heuston West.
A railway order for the line will be submitted to an Bord Pleanála by the end of this month.
National Transport Authority CEO Anne Graham said the project "will provide a major upgrade to rail services for passengers living along the rail corridor.
"This project will be particularly beneficial to commuters, as many of the DART trains will operate to and from Dublin city centre through the Phoenix Park tunnel to Connolly and Grand Canal Dock stations."
The new service Is promised to be at least twice as frequent as current service with up to 11 services per hour in each direction at peak times and capacity for up to four times as many passengers. The infrastructure is scheduled to be in place by the end of this decade
Commuters in Drogheda are being promised DART services to Dublin city from early 2025. This will be facilitated by the electrification of the line to Drogheda. The line to Maynooth and to the M3 Parkway will also be electrified and there will an upgrade for the infrastructure to Greystones.
The new services will be facilitated by the DART+ Fleet programme which will see Iarnród Éireann commission up to 750 new electric or battery electric vehicles over ten years, the biggest purchasing order in the history of Irish public transport.
The new trains will allow expansion of services while the lines are being upgraded and greater accessibility and more dedicated wheelchair spaces.
There will also be four bicycle spaces per carriage and charging points for e-bikes and e-scooters.
