Some road-building projects in the past had not been "up to the mark", but costs and controls had been improved in the past five years so that they now came in on time and under cost, Taoiseach Bertie Ahern insisted in the Dáil.
Mr Ahern said changes and expertise brought in by the National Roads Authority meant there were now far more accurate and effective estimates of costs.
He was responding to Green Party leader Trevor Sargent, who said that the cost overruns in the RTÉ Prime Time programme on a number of major projects were described as the "biggest abuse of taxpayers' money in the history of the State".
Mr Sargent also called for the Taoiseach to delay the signing of contracts for toll roads, "which is going to make enormous profits for private builders over the heads and at the costs of taxpayers for years and years".
He blamed the decisions by Government to "ditch" the National Road Needs study and then to begin "cooking up an ad-hoc notion to not upgrade the roads but replace those roads with motorways".
He said: "What we have instead is a motorway plan which is not rooted in sound traffic management or sound financial management. That has been proven", and a plan estimated at €5.6 billion could now cost up to €20 billion.
Mr Sargent said that a trick employed by contractors had become systematic, where they put in a bid "low enough to get political support and once accepted the claims are maximised to ensure that the overrun is not 20 per cent over, which is the average internationally, but 86 per cent of the cost".
But the Taoiseach said the NRA had changed the "loose" system and structure of road-building contracts and brought in structures and expertise and now had far more cost-effective contracts. Mr Ahern said, however: "The early schemes obviously were not up to the mark, and that is why in the last five years the NRA has strengthened cost estimation and the control procedures".
The previous roads programme was "a particular programme for a limited number of roads. It has been expanded enormously in the last number of years with 68 projects and 120km of roadway and just short of 120km of dual carriageway built".
The projects were now on time and under cost.
