When I was in Hue, Vietnam, I met four schoolteachers who all lived in a single-room shack. The four women could only afford two bicycles between them, so the way they commuted was two to a bike--with the one sitting on the rear placing her feet on the pedals alongside the driver's feet and pedaling in sync. It seemed they'd been doing this for years. "More faster," one of the teachers cheerfully explained to me, "less tired."
I can't tell what country the following video was shot in, though it also looks to be somewhere in Southeast Asia. In any case, these two clever kids have also figured out a way to share a single bike between them:
I am dying to know A) How they thought this up, and B) How they get started!