If we don't ask too much about production methods, bicycles are the cleanest vehicles on the planet. Powered solely by human energy, they keep cities' air clean, occupy less space and are the second cheapest method of transportation. Walking is even cheaper, but that might change depending on your shoes.
Specialized, a bike manufacturer, and Google have teamed up to create the Innovate or die contest. What's this about? Easy: Create the most amazing pedal-powered machine you (or you and up to four of your friends) can create, film it, upload it into YouTube and if you're the winner, you'll receive $5,000US. Finalists will get Specialized bikes and 200 contestants will get t-shirts. The t-shirts, according to the site "may provoke compliments like Nice shirt".
So how's your imagination? Good? Submit your ideas before December 15th. Some are already working on it.