the atlanta streetcar is exactly that. it relies on overhead lines. it still requires completely new infrastructure.
ND40 may understand more of the actual electrical side of things but the power in the transmission lines is probably not directly usable by the streetcars. you would need a series of transformers to convert it to a usable system, at that point you can't put it back into the existing lines. you will need a second power line to run the streetcar.
I think you lose a lot of flexibility when you tie a system down to the powerlines. just today in Atlanta I saw a MARTA bus pass some vehicle pulled over on the right. your system wouldn't allow for that. you need a system that is completely separate from the road to really allow a tethered system to work.
funny enough Atlanta is proposing an autonomous system that does just this thru two very fixed points with a completely separate "road" for it to run on. Its EV, but I don't think they are doing the power lines. we will see how/if it works out.
Combining the driverless technology of autonomous vehicles with the dedicated thoroughfares of light rail, a wholly new kind of public transportation is coming to Atlanta.
www.thecooldown.com