One thing I've noticed re: failure to plan is the lack of provision for future motorway junctions. The N7 from the M50 to the M9/M7 split has at least 3 more junctions on the way with no numbers reserved for them:
Newlands Cross (1A?)
Tootenhill (4A? - west of Rathcoole)
Future Leinster Orbital (10A? - west of Naas)
Since the stretch was renumbered only a few years ago, this really is ridic.
Not heard of a future junction at Tootenhill but there is going to be one for the Sallins bypass/Osberstown at some point also, 9A I'd assume.