The route history, that is, how the RTA came to be, is quite complicated. Rather than try to explain it with words, see the graphic below to get an idea of where and when the various street railway companies, starting with horsecars, progressing to streetcars, and then trolleybuses, came to be. At some future point, I'll update this with the various interurban lines.

Dayton ETB Route History until 1947
Dayton ETB Route History after 1947