Ironically, this was what NYC (technically, pre-NYC) did over 100 years ago -- there was a thriving network of streetcars in Brooklyn[1], which overlap almost exactly with neighborhood density. We then tore them up, leaving just the subway lines and a bus system that traces the vestiges of the old streetcar lines.

Streetcar suburbs[2] not only work, but are imminently sustainable compared to other forms of urban/suburban extension.

[1]: https://en.wikipedia.org/wiki/List_of_streetcar_lines_in_Bro...

[2]: https://en.wikipedia.org/wiki/Streetcar_suburb