"The thing from the exhaust is the same that we breathe," said design stufent Edwin Yi Yuan, referring to the Green Speed Air motorcycle, a concept bike intended to run on compressed air. A rotary air engine fed by high-pressure air tanks means no gas, no combustion, no exhaust--and no gearbox or shifting either, due to a single gear at a 1:1 ratio.

Built as a student project at the Royal Melbourne Institute of Technology, the GSA bike is intended to be a land racer, which also obviates the need for a headlight and tail-light. But the compressed-air technology is not without its problems:

It [air power] has lower mileage than petrol. I mean to cover the same distance, you need a lot more volume of compressed air than petrol. That means we're either going to have to go to the gas station more often, or have a huge heavy tank on the bike which makes it very heavy. Even a dangerously high pressure air tank still cannot compare to petrol for power to volume figure.

Though the academic portion of the project has ended, Yi Yuan continues trying to solve the project's problems with professor Simon Curlis, and the pair hope to advance the GSA into a fully-functioning prototype. Read all about it here.