re: Hybrid car chassis
There is a lot of plastic in most modern cars. Reducing weight has been the first thing engineers have been doing for years to make mileage targets.
The "Superbus" looks cool, but effective use of available internal and external space on a crowded street probably makes the conventional "boxy" bus the most efficient overall design. This is particularly true since most city buses don't travel fast enough to make aerodynamics a major issue. The one door (actually, there's usually two) limits mechanical issues, and of course, you can't let the left-side passengers off on the traffic side anyway.
There's a hydrogen-powered fuel cell bus I've seen around here. Apparently cryogenic--the rocket-like misting vents are on the top.