The National Roads Authority (NRA) has blamed inflation in the construction industry for the huge increase in its target budget.
In an address to the Dáil Public Accounts Committee (PAC), the NRA's chief executive Mr Michael Tobin said inflation was the main reason for the National Roads Programme budget increasing from just under €6 billion to €14 billion.
Mr Tobin also cited the addition of new projects as a factor in the budget overrun.
When first announced in 1999 the National Development Plan promised a network of motorways, dual carriageways and roads completed to be completed by 2006 at a cost of just under €6 billion.
The current estimate for the programme is €14 billion and the Minister for Transport predicts the completion date will three years behind schedule.