Well, if you're curious, Greater Paris's line T4 partly implements such a 'tram-train' already.
I think Wiki's article is good enough to begin with.
https://en.wikipedia.org/wiki/%C3%8E...tramway_Line_4
Was the 1st line in France to implement that technology to solve the problem of railroad crossings along.
Only partly, however, cause it doesn't cross any real urban environment or street.
It is nonetheless an available option for some prospective extension of it, but for now, it's just an old line that needed lighter vehicles to deal with railroad crossings.
This hybrid tram-train tech is only in an early stage here, so it doesn't seem fully satisfying or efficient yet. Further experience will bring about improvement.