Passenger numbers on the Enterprise train service between Dublin and Belfast are down 60% since part of the track collapsed in August.
The cross-border service is jointly run by Iarnród Éireann and Translink in Northern Ireland.
The drop in passenger figures was revealed by Northern Ireland Regional Development Minister Conor Murphy yesterday.
It has been almost two months since the viaduct crossing the Broadmeadow estuary in north Dublin fell into the sea.
Repairs to the 20 metre section of railway line are expected to be completed by the end of November.
In the meantime, special bus services ferry rail passengers between Dublin and Drogheda, adding an extra 30 minutes to the normal journey time between Belfast and Dublin.
Research carried out by Translink indicates that the majority of passengers who have stopped taking the train since the collapse of the bridge now travel by car.
It is estimated that the disruption will cost Translink somewhere between £1-£2m in lost revenue.
