Some €3.3 million has been spent on fees to consultants for Dublin Metro before a sod has been turned on the project.
Figures released by the National Transport Authority show engineering and design firm Arup received €186,000 in 2016, €1.3 million in 2017 and over €1.3 million to date this year for work on the proposed rail link.
Another major engineering company Aecom was paid €13,000 in 2014, €305,000 in 2015 and €16,000 in 2016 for its involvement. Engineering giant Jacobs was paid €182,000 between last year and August this year.
Smaller amounts were also paid to planning consultants Brady Shipman Martin (€7,000) and law firm McCann Fitzgerald (€6,000).
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Details of the preferred route, which combines the previously planned Metro North from Swords to the city centre with an upgrade of the Luas Green line between Charlemont and Sandyford, were announced last March.
Work on the 26km route, 12km of which will be underground, is due to start in 2021 and to take six years.
Around 100 properties will have to be purchased to allow for the €3 billion plan to go ahead.
Already earmarked for acquisition and demolition are College Gate, a complex of 70 apartments next to Tara Street Dart station, and the Markievicz Leisure Centre, refurbished two years ago by Dublin City Council at a cost of more than €1 million.