Two new super-long Luas trams which cost the State €4m each have been taken out of service, the National Transport Authority (NTA) has confirmed.
The 55-metre-trams were introduced on the new Luas cross-city Green Line just before Christmas.
However, they have been withdrawn from service while technicians try to determine the cause of a technical fault, NTA chief executive Ann Graham said yesterday.
She apologised to passengers who have complained of over-crowding, bottlenecks and slow service, delays and other glitches since the cross-city went into operation in December.
"The main issue has been the availability of fleet, but we would recognise that it has been a sub-optimal service," she said.
An NTA spokesman said five other 55-metre trams are due to come on stream in the coming months once the fault is corrected.
"Technicians are working on rectifying the fault," he said last night, but added that the faulty trams are not the only issues that have plagued the roll-out of the cross-city service.
A number of trams are not in service because of a backlog awaiting maintenance at transport company Alstrom in Sandyford. The backlog is due to recent renovations at the depot.
Ms Graham said the NTA, Transport Infrastructure Ireland, Luas operator Transdev and Alstrom are meeting daily to resolve the problems.