Commuters on the Drogheda and Belfast Enterprise services and northbound DART users suffered severe delays yesterday when the line between Connolly and Kilbarrack stations closed for repairs.
The damage was caused by the collapse of casing on a gas pipe on a bridge over the railway line on to overhead wires.
An Iarnród Éireann spokesman said last night the damage was not as bad as initially feared and it was "virtually certain" services would return to normal today. Initially, the company said the disruption was likely to continue "well into" today and possibly tomorrow.
The company laid on bus transfers for commuters on the Belfast service while DART users were allowed to use their tickets for transfer on to Dublin Bus routes.