The underground system has faced significant delays over the past 20 years.
More than €150m has been spent on Dublin's Metro up to the end of last year - despite no "significant" physical work.
An estimate of the project - which would run from Swords, through the airport and into the city centre - puts the cost at around €9.5b .
The underground rail system has faced significant delays over the past two decades.
Speaking at the Public Accounts Committee, its chair, Laois Offaly Sinn Féin TD Brian Stanley, says the cost of preparatory works are "astronomical":