Differences over when the Luas Green line should be converted to a higher-capacity metro system emerged at the public inquiry into the extension of the route to Cherrywood yesterday.
Chief executive of the Dublin Transportation Office (DTO) John Henry told inquiry inspector James Connolly SC that population growth figures "strongly suggest that rail capacity on this corridor would need to be expanded in the medium to longer term".
Mr Henry said the Government strategy, Platform for Change, was committed to converting the existing Green line and its proposed extension to a metro service in the medium term.
"I have made known to the RPA my view that it would be prudent to develop a detailed plan for the upgrade of the line."
However the Railway Procurement Agency (RPA) told the inquiry the higher-capacity metro would not be required in the medium term, and that Luas was the "appropriate transport solution" capable of handling passenger numbers "up to and beyond 2020".
The agency is seeking permission to almost double the length of the Green line, adding another 7.5km (4.6 miles) to the 9km (5.5 miles) route from St Stephen's Green through Sandyford via Carrickmines to Bride's Glen at Cherrywood.
While RPA transport planning manager Tom O'Reilly said the design of Luas "does not preclude" conversion to metro, the platforms would have to be be extended from 40m to 90m, and road interchanges altered to ensure permanent priority.
In addition, because metro was faster some stops on the Luas line were too close and would have to be closed.
Mr O'Reilly questioned whether the time savings due to a metro travelling faster would compensate for passengers walking further to metro stations.
He said the fleet of 12 carriages being procured for the service would be sufficient to provide for demand up to 2016, and after that capacity could be increased further by extending trams from 40m to 50m and increasing their frequency.
He said "forecasts suggest that the capacity requirement on this corridor will not require metro services until beyond 2020".
He concluded: "Luas is the appropriate transport solution on this corridor to meet the short and medium-term forecast transport demand."
The proposed Luas extension would add 11 new stops to the Green line. The proposed route deviates from the former Harcourt Street railway to pass east of Leopardstown racecourse before rejoining the original alignment at Carrickmines.
Under the Government's strategy Transport 21, the route is to be extended to Bray by 2016.
Some 50 per cent of the estimated €200 million cost of the route is to be provided by landowners in the vicinity of the route and in the Cherrywood area. Dún Laoghaire-Rathdown County Council is expected to make a lengthy submission to the inquiry on planning issues, starting tomorrow.
