Cormac Rabbitt, one of the key figures in the Mitsui and Nishimatsu offer to build a metro system for Dublin in 2000, said the RPA was making an expensive mistake in not mirroring the 'one stop shop' approach now favoured by the National Roads Authority (NRA) for major road projects.

"The NRA puts a consortium together that will do the procurement, the Environment Impact Assessment, the design, the building, before the order is even made.

You are now seeing those projects coming in five, eight or 12 months ahead of schedule.

With the metro, the line is being laid out and the preliminary design is being done and only then is the private sector being involved.

"They are going down the way of a public works project instead of the public private partnership one-stop shop and it will cost considerably more because of that.

They are breaking all the rules on efficient metro building, " he said.

Rabbitt also questioned why the option of using the defunct, but existing, Broadstone to Cabra/Finglas railway line . . . which could serve the planned DIT college at Grangegorman before continuing on to Ballymun and the airport . . . was not used for the line. This route is four kilometres shorter than the RPA's planned proposed route, offering "significant savings", he said.

Rabbitt also criticised the decision to run the metro on a different rail-track gauge to the national rail system, which prohibits connecting the two systems. "In other countries, they use the same gauge on their metro system as on their national network, " he said.