One issue here, though, is that US urbanisation is _weird_. A lot of that 'urbanisation' is vast suburbs of detached houses; it's not very dense at all.
New detached houses have become quite rare here in Ireland, except as rural one-offs; most new suburban houses would be semi-detached (duplex in US terminology, I think; duplex means something else here, just to confuse the issue) or terraced (townhouse in US terminology, I think?), interspersed with mid-rise (~6 story) apartment blocks. They'd also be much smaller; average size of a new home here is ~100sqm, vs 250sqm in the US. Same goes for the UK, only moreso (average size of a home is a bit smaller there).
All of this obviously leads to much higher density. Planning rules effectively ban detached houses in many suburbs, as a minimum density is enforced. The higher density you have, the more effective public transport systems are.
Suburban apartment blocks also seem to be somewhat rarer in the US.
