Bus journey times through parts of Dublin city centre have more than doubled since new Luas lines opened, an Oireachtas committee has heard.
City Council chiefs said that between 9am and 10am, it takes an average of 23 minutes for a bus going from north to south to navigate College Green.
Before the Luas Cross City lines came into operation, it took about 10 minutes.
Changes to pedestrian crossings have also led to waiting times at lights taking twice as long, Dublin City Council chief executive Owen Keegan said.
He also said potential gridlock had been well-flagged before the new lines opened.
"It was always recognised by the city council that College Green, which has only one lane in each direction, would not be able to accommodate the same number of buses and taxis," Mr Keegan told the Oireachtas Committee on Transport, Tourism and Sport.
Dublin Bus chief executive Ray Coyne said that 17 routes have been realigned to ease congestion in College Green and another 10 will be moved out of the area on March 5.
Longer, 55-metre Luas trams operating more frequently will be travelling through College Green by the end of March.
They will be given priority at lights to avoid blocking traffic on the quays while crossing O'Connell Bridge and the Rosie Hackett Bridge.
Peter Lunden-Welden, chief executive of Luas operator Transdev, told the committee that seven new long trams will be on track in the first week of May. Transdev will also be seeking 26 trams to be extended and wants to buy another eight.
"Whatever we put in place for Luas, it seems that will not meet demand. My prediction is that will not solve the congestion. There will be higher demand," Mr Lunden-Welden said.
The Luas boss told the committee that since the Cross City line opened, tram journey times through College Green have improved by three to four minutes.
Mr Coyne said the average peak-time bus speed in the city is 14kph, with the aim to increase it to 18kph.
However, he warned there are few viable options for taking buses out of College Green. Only Parliament Street and Westland Row offer nearby routes to traverse the city centre.
Conor Faughnan, of the AA, said the fallout is still being felt from a 2009 decision to ban cars, except taxis, from College Green.
"Put simply, there's no room for buses and trams," he said.