The Interconnector, as it is futuristically called, will, they say, treble the capacity of rail services in greater Dublin from 33 million passengers to over 100 million.

In case you are a little confused, no, this is not the separate Metro project between St Stephen's Green and Swords which the Rail Procurement Agency promises will be built by 2012. And, no, you haven't lost it altogether - yes we have heard about The Interconnector before. This is a 2002 plan - that's right, a 2002 plan - costed five years ago at Euro1.3bn.

Costings for last week's plan won't be ready until November. But no matter: the way these things go, it's probably just as accurate to have a guess - 'pick a number, any number' style - at the final bill to the taxpayer. Oh, let's say Euro2.6bn by the time it's built in 2015.

2015? Yes, the first kango hammer does not hit the ground until 2010 and they're hoping to have it built within five years from then.

An exact route has yet to be decided, including where the main underground stations will be. Then it goes to An Bord Plean�la, and the various objections, appeals, claims, counter-claims and rows over compensation have to be suffered and settled.

Iarnr�d Eireann insists the new routes, the new trains, the vastly improved frequency will happen.

But you can't blame commuters for being cynical.

Transport minister Noel Dempsey promises he'll hurry up the legislation to set up the Dublin Transportation Authority which will co-ordinate all Dublin's traffic initiatives.

But, as good as it is on paper, this new underground won't physically connect with the airport Metro, which is also partly underground, because the rail gauges are different. That means we have to build two tunnels. And nobody, not even minister Dempsey, knows when the Green and Red Luas lines will be joined up.

As for integrated ticketing - at least if nothing's built before 2015, it gives the transport authorities a long lead-in to prepare.

Nice plan, good graphics, great maps: Dubliners should go and look at it when it's on display on Tuesday. But in the meantime, they'll have to find another way home. M50 anyone?