There are more than 4 million miles of paved roadways in the United States. Increasingly, renewable energy advocates are looking at all that asphalt and seeing a lot of untapped potential. What if the nation's highways and streets weren't just a way to get from here to there? What if roads actually could be used to generate electricity?

It's an idea that's being explored in much of the world. A company in Japan is trying to capture the vibrations from traffic driving over a bridge and convert the energy to electricity. Engineers in Israel are testing a method of producing power by embedding special crystals in asphalt. (The pressure from passing cars causes the crystals to vibrate and produce tiny electric fields.) A researcher in Houston has proposed capturing the tailwind behind cars using rows of small turbines housed in roadside Jersey barriers.

Scott Brusaw wants to go even further. The electrical engineer from Idaho envisions paving roads with 12-foot-square solar panels. Brusaw already has built a prototype, and his work got a big boost in August from the federal Department of Transportation, which awarded his company a $100,000 research contract to develop a full-scale model for testing by February. The potential is staggering. Brusaw likes to note that if all roads in America were paved with solar panels, they would produce three times as much energy as the country currently consumes.

Solar roads would produce other benefits, too. Heat from the panels could be used to melt snow and ice, eliminating the need for snowplows. LED lights in the panels could be used to send information to drivers or to change traffic flow by virtually re-striping the lanes. And an electric road could conceivably power electric vehicles while they drive.

The idea still faces some major hurdles, to say the least. One is technical: The panels must be covered with glass. Although glass is as strong as steel, it's far more brittle than asphalt. It also would have to be self-cleaning (so that dirt and grime wouldn't obscure the solar panels), textured (to allow tires to grip the surface) and situated in a way that would allow water to run off it. Then there's the issue of glare. "Nobody's ever really driven on glass for any period of time before," Brusaw admits. Cost is an even bigger hurdle. The price of the panels is about $10,000 each--significantly more than asphalt or concrete--although Brusaw claims that when you factor in the environmental benefits plus the power plants that won't have to be built, the costs are comparable.

Tacoma, Washington, has offered itself as a solar-road test market. Public works director Richard McKinley invited Brusaw to the city to present his idea, which McKinley calls "one of the most green and sustainable concepts out there." Is it all just sci-fi fantasy? Perhaps. But it's not so difficult to imagine a city trying it with a parking lot first--and if that works, seeing where the road leads from there.