The Taoiseach, Bertie Ahern, has once again refused to give an estimate of the cost of the proposed Metro project saying it "would be a nonsense to do so".
Speaking during Leaders Questions in the Dail this afternoon Mr Ahern said that to give an estimate of the cost would skew the process and not ensure best value.
He said that the Railway Procurement Agency (RPA) had made "careful assessments of the costs of this huge project" and the tendering process would be totally transparent.
Mr Ahern was responding to a question from Fine Gael leader Enda Kenny who said the M50 upgrade was also a public private partnership project but that the government had given an estimated cost of that before the tender process was complete.
The Taoiseach said that there were probably just six to 10 international companies capable of completing a project of this scale and the priority was to ensure they all tendered for it.
Responding to a question from Labour Party leader Pat Rabbitte on the costs of compensation awarded by the Residential Institutions Redress Board, Mr Ahern defended the figure of €1.2 billion and said it could not have been foreseen.
Mr Ahern said there had been 14,000 applications for compensation but initial estimate from the Department of Education was that just 7,000 former residents would come forward.