A decision on the preferred route to link up the two Luas lines in Dublin city centre is to be made by September.
Five options are under consideration, but whichever is chosen, construction will see Dublin's main city centre thoroughfares being dug up for at least two years, the Railway Procurement Agency (RPA) has acknowledged.
The RPA yesterday said there could be "no gain without pain" and warned Dublin Bus - which provides almost seven times more passenger journeys than the Luas - it will have to alter some of its busiest routes during construction.
Dublin Bus would also have to permanently move some of its bus stops after the construction period, according to RPA chief executive Frank Allen, who said: "You can't have a tram with 300 people on board stopped at a bus stop."
While other public transport would be able to share the space, private cars and commercial traffic would be banned from the route permanently. The RPA also said the 7.5km (4.7-mile) Cherrywood extension, which it expects to begin building this autumn, would not be completed until 2010.
The RPA said the route for the city centre connection, Line BX, had not yet been selected. It acknowledged that an important criterion was which route was the shortest, as some of the longer ones might not be faster than walking between Luas lines.
The RPA said that in any event, the line would be continuing on through the north city to Grangegorman to bring the benefits of tram service to communities there.
In relation to the Cherrywood extension, the RPA said a significant number of bridges were required as the line crossed and recrossed the M50 motorway.
The work also involves realigning the Ballyogan Road and crossing another new central spine road near Carrickmines.
The revelations about disruption during construction marred what should otherwise have been a day of vindication for the RPA. After years of criticism during the construction of the initial two lines, the agency has delivered a fine transport system.
Few transport issues have been as contentious as the construction of the Luas but, since its completion, the city has embraced the service in significant numbers.
Questions remain about the length of time needed to build new elements. While the RPA argues the Cherrywood extension is complex, it also runs largely through what is open countryside. If it takes 3½ years to construct, it will work out at just over 2km a year. The Nassau Street/College Green axis, at about 1.5km, works out at a rate of about 0.75km a year.
