They don't need silly suspension railways in most places. A tram line fits perfectly in 1 lane, so that would make it 2 lanes for both ways. US lanes are so wide that it's likely 2 tram rails fit in 1.5 road lanes, with a bit of extra room for wider sidewalks (sorely needed in most of the US), bike lanes (also sorely needed in most of the US) or just general greenery (hedges would do wonders for US urban landscapes...).
Of course this would require that the 3-4 lane stroads give up 2 of their carlanes so instead of doing the reasonable thing, building infrastructure costing 10x is almost universally preferred.
Heck, it doesn't even need to be a tram. BRTs are good enough for a lot of cases.
Well-done BRTs are probably the best thing you can get for cost/benefit. And you can subway them at points if you want, and if they get super popular you can put them on rails.
Of course this would require that the 3-4 lane stroads give up 2 of their carlanes so instead of doing the reasonable thing, building infrastructure costing 10x is almost universally preferred.
Heck, it doesn't even need to be a tram. BRTs are good enough for a lot of cases.