The Railway Procurement Agency (RPA) hopes next week to announce a date for the opening of the second Luas line at the end of September, a month after its original due date.
The RPA said it had been reluctant to give an exact date until now because it did not want to be accused of missing targets.
However, it was confident that next week it would be in a position to make an announcement on the Tallaght-to-Connolly Station line.
"The tests on the line have been going very well, we're running trams at a 10-minute frequency, so I'm hopeful we'll be able to set a date next week and I'm very hopeful that it will be at the end of September," RPA spokesman Mr Tom Manning said.
The new "Red Line" had been scheduled to open at the end of August but the length and complexity of the line had led to delays, he said.
"It's much more complex than the Green Line - it's nearly double the length and there are far more junctions along the way and the signalling system is quite complicated, but we're at the fine-tuning stage now."
The Green Line, from Sandyford to St Stephen's Green, is 9 km long, has 13 stops and six junctions. The Red Line is 15 km with 23 stops and 34 junctions. It will take 43 minutes to reach the end of the the Red Line, almost twice as long as the Green Line at 22 minutes.
The RPA had not encountered any problems during the testing of the Red Line, Mr Manning said, and even though more than twice the amount of Red Line track was on-street, there had been no problems with motorists or pedestrians.
"I think motorists are quite used to the Luas from the Green Line," he said.
When the new line opens, it will operate free of charge for the first five days. Adult single journey tickets for an end-to-end trip are €2 on both lines. However, a single child ticket will be more expensive on the Red Line at €1, compared with 80 cent on the Green Line.
Some 700,000 passengers used the Green Line from July 5th to August 5th.
