It is expected that a large section of the green Luas line in Dublin will not re-open until tomorrow morning at the earliest.
No trams have been running between Balally and Brides Glen since yesterday evening, because of a power fault.
Engineers are still working to identify the source of the problem in the Stillorgan area.
Ciara Egan from Transdev, which runs Luas, said replacement bus services were in operation.
She added: "There's no Luas service between Ballally and Brides Glen...Dublin Bus are accepting Luas tickets for the duration of the disruption."
Meanwhile, a crash is causing long delays on the M7 heading south just after junction 10 Naas South.
The left lane of the motorway is currently blocked. Drivers approaching the area from Dublin and the M50 are advised to divert if possible.
It is not yet known how long it's going to take to get a large section of the green Luas line in Dublin back up and running.
No trams have been operating between Balally and Brides Glen since yesterday evening, because of a power failure.
The fault is affecting thousands of shoppers getting to Christmas sales, and thousands of horseracing fans heading to Leopardstown.
Racing and operations manager at Leopardstown David Attwood said they had made changes to their shuttle bus service to help. Their shuttles will run to Leopardstown from Balally Luas stop, and back from Leopardstown to Balally this evening.