I was in Seattle at the weekend and took a ride on their old monorail. For those not familiar with it, it sits on stilts about two stories above the streets and has no cables hanging from above as all the electrics/motors are under the train.
Ok, so it's an ancient relic from the '60s and it only goes for a mile or two, but I thought it was an interesting alternative to street trams, such as the Luas.
The roads would only have to be dug up to support the columns on which the track lies (therefore no need to dig up the other utilites such as water/gas/electricity) and the trains themselves don't interfere with traffic.
And seeing that stilts seem to be in favour in Ireland these days....