As I pointed out before, DDOT has no plan to avoid using overhead lines to power streetcars. I have blogged about onboard vehicular power storage, namely supercapacitors and batteries. I engaged in some dialogue about this on Greater Greater Washington. I have done a little research and found yet another method to store power: flywheel power storage. An English company, Parry People Movers Ltd., has been doing work on this. They even have implemented a diesel prototype. Its partner, JPM Parry & Associates claims to be designing a 220-passenger light rail vehicle, in a multiyear effort. While electrical power is a possible source, neither website has information about how long a vehicle could run on it.
A possible compromise position for DC streetcars is to use electrical power storage with charging umbrellas and a diesel or turbine engine. This is an engineering task. DDOT does have engineers, doesn't it?