Capacity on the notoriously overcrowded Dublin-Maynooth railway line will increase by 40 per cent at peak times from early next month.
However, Iarnród Éireann has warned regular commuters that they can not be guaranteed a seat.
The expansion of services on the Maynooth line is one of a series of improvements announced yesterday by the company.
The northern commuter line from Drogheda to Dublin is also being enhanced - with an extra morning peak service.
A new early morning commuter service will be introduced from Athlone to Kildare, and frequency will be increased seven days a week on the Cork-Cobh and Cork-Mallow commuter services.
However, the biggest improvements are earmarked for the Maynooth line, with three new morning peak services to Connolly Station and two evening peak services.
Iarnród Éireann spokesman Barry Kenny said the improvements would boost passenger numbers on the line by one million next year.
Asked whether it would mean an end to standing on trains, however, he replied: "No. Commuter services are about full loading. Every time we put on extra services they fill up, and this will fill up very quickly.
"On Intercity services we want to see an end to people standing but it's part and parcel of commuter services," he added.
Other improvements announced by the company are extra peak-time Dart services to Malahide and Portmarnock; an expansion of services to Gorey; and increased frequency on Intercity routes such as Dublin-Sligo and Dublin-Cork.
A €70 million investment in 36 new railcar carriages would mean a phasing out of "the bum-shakers" in Co Kerry and elsewhere, Mr Kenny noted.
All the improvements will be introduced from December 11th.
A further enhancement of services in Co Waterford, Kilkenny and Carlow, including the introduction of a new commuter rail service from Kilkenny to Dublin, will be introduced on March 27th next.
Minister for Transport Martin Cullen, who attended the publication of the plans, said: "I'm really delighted with the attitude of can-do about Iarnród Éireann at the moment. It has been a huge transformation from a company that was really left behind for many, many years."
However, Labour TD for Dublin West Joan Burton accused both Iarnród Éireann and Mr Cullen of "re-announcing" the same expansion in services on the Maynooth line - known locally as the "Calcutta express".
She said the proposals were "greeted with derision" by the local community when first announced as they were inadequate to meet the needs of a rapidly growing population.
