There are more than 4 million miles of paved road in the United States, and 93 percent of them are covered in asphalt. Unless you're backpacking in the wilds of Alaska or wandering the bayous of Louisiana, you are never more than 22 miles from a stretch of blacktop.

That's a lot of asphalt, and a lot of energy needed to produce it - which is why Hussain Bahia wants to find a greener way to make the stuff. He's a civil engineering professor at the University of Wisconsin-Madison, and he says anything that increases asphalt's recycled material content or cuts the energy needed to lay it down will have a big impact on the environment - and our pocketbooks.

"This is a no-brainer," says Bahia, who has been studying asphalt for more than 20 years. "If any person involved in managing our infrastructure looks at the data, why would you spend more energy and money on something else?"

Bahia is part of a $5 million research program called the Asphalt Research Consortium, which hopes to, among other things, make blacktop more ecologically sustainable. One of his first goals is to develop "cold-mix" asphalts that require significantly less energy than conventional asphalt to apply.

Asphalt is about 5 percent oil and 95 percent sand and rock; it's made from a black, sticky byproduct of oil refining. It's too thick to be applied without being heated to 300 degrees Fahrenheit. That requires a lot of energy, which is why other countries have been using cold-mix asphalts - also called emulsions - for years. One method involves shearing asphalt into fine particles, then mixing them with water and soap-like chemicals called surfactants that hold the asphalt in solution until its laid.

Bahia says studies have shown cold mixes require seven times less energy than hot mixes and they produce less CO2 and other emissions. But they aren't widely used in the United States because hot mixes have worked so well, and there are no standards dictating how cold mixes are produced or how they'll perform. Bahia hopes to develop quality control tests and standards that will convince engineers and road builders to adopt cold mixes. Bahia wants to experiment with adding polymers or plastics to cold mix asphalts to further improve durability and make roads quieter.

"At U.S. refineries today, there are very mature, established specifications for hot binders," he says. "But for emulsions, there is no clear agreement on how to define the quality. So we have emulsions already, but we don't produce them as much because the specifications aren't as clear."

And until now, asphalt has been cheap, which is another reason hot mixes have remained the standard. But as the price of petroleum has hit record levels, so too has the price of asphalt - and the cost of applying it. Asphalt sold for $35 a ton a few years ago, but it's up to $80 and could hit $100. That has some states are scaling back repaving projects and looking for alternatives. Asphalt already is one of the most frequently widely recycled products in the country, but switching to cold-mix would allow the use of even more recycled products - which already include rubber, glass and concrete - when producing blacktop.

"Why are we spending so much money on something else? I think there's a very good reason - lack of sufficient knowledge," Bahia says. "And our job as a university is to provide the knowledge that will hopefully one day get us there."

Photo by Flickr user Fort Photo.