Engineers have had to reset dozens of traffic lights across Cork City after a major outage on the network on Wednesday morning.
An investigation is now under way to establish what caused the outage.
Motorists were baffled after encountering faulty lights at several busy junctions on key routes into and around the city centre.
Faults were reported north of the northern channel of the river Lee, at the bottom of Summerhill South, at St Patrick’s Bridge, as well as on the southern side of the channel at Christy Ring Bridge, and on several junctions up to and including South Gate Bridge.
A spokesman for Cork City Council described it as a “significant outage” on a portion of the traffic signal network.
“Investigations are ongoing as to the cause of this incident,” he said.
“Crews have responded and reset the majority of controllers which are now fully operational.
“We are continuing to work on the small number of remaining controllers which need to be reset.”