Washington’s Blog 
April 25, 2011
I wrote  yesterday:
Another use of a free, wasted byproduct to generate electricity is piezo-electric energy . “Piezo” means pressure. Anything that produces pressure can produce energy.
For example, a train station in Japan installed piezo-electric equipment in the ground, so that the foot traffic of those walking through the train station generates electricity (turnstiles at train, subway and ferry stations, ballparks and amusement parks can also generate electricity).
Similarly, all exercise machines at the gym or at home can be hooked up to produce electricity.
But perhaps the greatest untapped sources of piezo-electric energy are freeways and busy roads. If piezo-electric mats were installed under the busiest sections [a little ways under the surface], the thousands of tons of vehicles passing over each day would generate massive amounts of electricity for the city’s use.
A couple of readers thought that sounded nuts.
But as TreeHugger notes  today:
Copyright TNO  2011
The Dutch are well known for their ubiquitous bike lanes, to the point where Amsterdam is neck and neck with Copenhagen for the title of most bike-loving capital in Europe. Now, Denmark will have to come up with something big to match the latest plan from the Netherlands – the installation of solar panels in roads, starting with bike lanes.
Called the Solaroad , the project is the brainchild of Dutch research firm TNO . The idea is pretty straightforward: a layer of concrete forms the road itself. A centimeter thick layer of crystalline silicon solar cells is laid on top, and covered by a layer of toughened glass. The energy potential: 50kWh per square meter per year, which can then be used to power street lighting, traffic systems and households.
But it’s still an idea in development, which is why TNO, working with the Province of North Holland , the consulting firm Ooms Averhorn Group  and the tech firm Intech , is starting with a small-scale pilot program in the town of Krommenie, outside of Amsterdam. Scheduled for installation next year, the first Solaroad will hopefully allow its developers better implement many more throughout the country.
Now why not put a piezo-electric mat under the crystalline silicon solar cells, under the layer of toughened glass?
We’d get two different forms of energy generation at once…