Boring tunnels beneath the city centre for light rail would be a ridiculous waste of money and resources. Numerous European cities have light rail running through their city centres, so it's not an "only in Ireland" thing either. Any underground network should be built to heavy rail standards to maximise capacity and help get more cars off the streets (which are the actual cause of congestion - not the Luas. The plan for the College Green Plaza which would see that area and much of Dame Street being pedestrianised will also help free-up the cross-city Luas route). As I said above, the Luas is part of a multi-faceted solution to Dublin's public transport problems, not the silver bullet, and it's taking heat here undeservedly when the microscope should be on all the messing that has surrounded Dart Underground and Metro North.