The main idea here is that the bus stops of the City buses can double as a quick charging station using today's ultracapacitors and not waiting for the mythical EESU's.
This idea is not new, and some have used flywheel storage before, but the demo in Washington is. The regenerative braking and use of quick charging would make for very efficient non-polluting buses in the city, more practical than the tethered buses. They can also install batteries as added buffer. This is one appropriate niche in the use of ultra-capacitor technology.
A U.S.-Chinese venture is out to prove the benefits of quick-charge buses.By Tyler Hamilton
http://www.technologyreview.com/energy/23754/