When I was a little kid, I had an electronics kit, the kind where you connect transistor 22 to resistor 25, to capacitor 9, to diode 13, and it becomes a water level detecting kit. It also had an astounding proof of a scientific concept introduced to me in the fifth grade: sound is energy. For this proof, the kit instructed you to connect the microphone to the voltmeter and light bulb. And then scream really really loud into the microphone, which would lead to the bulb lighting up and the voltmeter jumping, as this was the kind of kit that grandparents buy their grandchildren, in order to annoy the parents. Parents, I'm sure you're quite familiar with this kind of toy.
Anyway, microphones do change sound into electrical energy, primarily because the electricity retains the pattern of the noise, but can be amplified, rerouted, edited, and a whole host of interesting tricks. Speaking into a microphone actually generates a tiny amount of power, which leads me to my idea.
Freeways often have tall walls built around them to cage in the annoying whooshing noise that the cars make as they zoom past at high speed. This noise now dissipates into the upper atmosphere instead of your windows. So I think we should take these walls....and line them with microphones, hooked to diodes, hooked to battery banks. I'm hoping that this will further dampen the noise as well, so it's win-win.
Well, except that physics is never totally win win. It'll probably slightly increase the air resistance or in some other way steal energy from the cars in a way only a physicist can explain.