MIT and the city of Copenhagen partnered for the development of the Copenhagen Wheel.

Say hello to the Copenhagen Wheel, a device that slips onto your existing bike wheel. It stores the energy that you already use, and saves it for when you need it most. Hills become flat, and you no longer have to expel loads of energy to get around …. It’s a device so simple, you’ll be amazed at what it accomplishes. It just might change the cycling world (and our planet) forever.

I live in a very flat area of New Zealand, so I don’t think I’ll be buying one. But … very cool idea. The Copenhagen Wheel is available for pre-order, at US$699. Shipping will begin in Spring 2014 (US time).