Ford and Georgia Tech is teaming together to convert a regular bus to a hydraulic hybrid, something which adopted widely, could save enormous amounts of gas.
Why a hydraulic hybrid system, and not a standard hybrid-electric? Simply put, regenerative braking powers a pump, that pushes fluid into a reservoir that provides power directly to the driveshaft at low speeds. This eliminates the need for a huge, expensive battery system, and hydraulic systems are probably better at moving those huge buses anyway.