One of the newest ideas in pavement technology is more than 1,000 years old. Just as all the roads that led to Rome were paved in cobblestone, today more and more roads are built with holes. A bad idea for lost change, but so-called permeable pavement''s environmental benefits pay dividends.

Whereas asphalt blocks natural drainage, permeable pavement lets the rain drip right into the ground, where soil filters out pollutants. And where dark asphalt makes surfaces hot, causing warmer runoff that can kill fish, permeable pavement''s lighter color reduces temperatures.

So far, low asphalt prices have kept the stuff relatively unpopular in the United States. But Germany and Japan readopted the Roman way years ago. "A lot of that has to do with their population," says Donna DeNinno of UniGroup USA, an association of pavement manufacturing companies. "They''ve got very large populations in very small areas."

American cities have started to catch on. Twenty-five percent of UniGroup''s products are now permeable, and next year Maryland and the District of Columbia will begin rebuilding some roads with permeable pavement as part of the Mid-Atlantic Green Highways Partnership.

The new technology has a new look and feel, says Charles Taylor, general manager of Advanced Pavement Technology. "If you drive at a low speed and have your windows down, you can probably hear the tires moving over the pavers," Taylor says. "But it''s not a bumpy ride."

This story appears in the March 26, 2007 print edition of U.S. News & World Report.