You seem to be thinking of trams, while nimos is talking about trolleybuses, which are buses that draw their power from overhead wires [0]. Specifically they're

You seem to be thinking of trams, while nimos is talking about trolleybuses, which are buses that draw their power from overhead wires [0]. Specifically they're suggesting that a hybrid option with batteries would reduce the need for wires everywhere (just run on battery power), but would still allow the buses to charge while connected to the overhead wire. [0] https://en.wikipedia.org/wiki/Trolleybus https://en.wikipedia.org/wiki/Trolleybus