The piezo bridge

This is the Sakura bridge, in Tokyo. It's part of the Shuto expressway, which is running straight through the city. As everybody who lives near a busy road knows: loads of traffic creates a lot of noise, a lot of dirt and... a lot of vibrations. All of these things can be considered a nuisance. But in Tokyo the decided to turn things around, and use one of these nuisances for to create a beneficial situation. They made use of Piezo electricity. The principle is that certain materials (i.e. specific ceramics and chrystals) produce an electrical current when mechanical pressure is applied. And the vibrations of the traffic do just that: they produce a continuously changing mechanical pressure. This leads to electricity that is being produced. This way, the bridge supplies the energy that is needed for the illumination of the bridge.

I'm well aware that this is just taking the ineffectiveness of the combustion engine and create something worthwile with excess energy, but still it is a fascinating idea to begin with.