Some trains were delayed by more than two hours on the first day of a new hourly train service between Belfast and Dublin.
The new Enterprise schedule began on Tuesday weeks after the opening of the new Grand Central Station in Belfast.
After a €25m cash injection from the Irish government, daily services between Belfast and Dublin have doubled from Monday to Saturday.
However, passengers suffered delays on a number of trains on Tuesday evening due to a major signalling fault in Dublin.
The delays affected four trains departing from Dublin and one late train departing from Belfast.
Iarnród Éireann apologised for the delays but said the feedback on the opening day of the more regular services was “positive”.
Stormont Infrastructure Minister John O’Dowd said this week that the new service was a “huge boost” for cross-border public transport.
