The Science of Sustainability

Building Better Roads with Next Generation Pavement

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Pavement

A test patch of pavement at the UC Pavement Research Center.

If you’ve driven around California lately, you might not be surprised to hear that the state’s roads and highways aren’t in great shape. A third of Bay Area roads are in poor condition and funding is dwindling on the state and federal level. That’s something Congress is discussing in Washington this week.

Meanwhile, researchers at two University of California campuses are trying to find ways to stretch those sparse dollars by making pavement quieter, greener and more durable.

Saving the life of roads

John Harvey of the UC Pavement Research Center is a sort of pavement doctor. "A pothole is when you put the electric paddles [to it]. The pavement is dead. You should never get to a pothole." You can probably guess what he talks about on long car trips. "Actually I’ve had people threaten to kick me out of the car."

The Heavy Vehicle Simulator in action at UC Davis

At UC Davis’s pavement testing facility, a huge machine is rolling a truck tire over a patch of asphalt. "It goes back and forth," says Harvey. "We’re probably looking at 20, 22,000 repetitions a day."

This machine simulates years of traffic in just weeks or months, which shows whether a pavement will last or fall apart – like the rutted test patch Harvey shows me nearby. "There’s all kind of cracks all over it and that is a structural failure." Roads fail because of repeated stress, especially from heavy-duty vehicles. "We only really design for truck traffic. You don’t even count the cars. They’re irrelevant."

If a road’s first enemy is trucks, its second is weather. Temperature changes from night to day, or summer to winter, cause roads to curl. And just like a paperclip, if you bend it enough, it breaks. "You get enough cracking, the cracks connect up. And so the piece is just sitting in there with no connection and it pops out under traffic." Cities often fill potholes as a stop-gap, but Harvey says it’s a temporary fix. "Maximum life of a pothole repair: one year."

Of course, the hurdle to fixing roads is cost. In 2009, Caltrans estimated that it needed more than six billion dollars to repair state highways. With the state budget in trouble, it got 1.5 billion.

Federal Aid Highway Act of 1956

Samples of asphalt being tested at UC Davis.

Back in the 1950s, road funding was plentiful. Car sales skyrocketed after World War II, which led Congress to pass the Highway Act, providing 51 billion dollars to be spent on highway construction. Around the same time, the Pavement Research Center was founded at UC Berkeley, just as engineering professor Carl Monismith arrived on campus. He says with the building boom, the state and federal government needed funding to maintain the roads. So, they set up gas taxes. "The California tax in 1963 was 11 cents. And that bought a lot. It’s probably 18 cents now at the most."

Gas tax revenue has also fallen as cars have become more fuel efficient. That’s led analysts to predict that the federal Highway Trust Fund will be bankrupt by 2014. Monismith says many cities are already behind on maintaining their roads, so it’s tough to build new durable roads, which are more expensive. "The Roman roads have lasted, what, twenty-some hundred years. But we couldn’t build them like that today."

The good news is – given the country spends an estimated 100 billion dollars a year on roads, even small improvements make a big difference.

Quieter pavement

Researchers use the microphones on this “noise car” to measure the sound coming from the tires.

In a garage at UC Davis, John Harvey shows me what they use to test some of those improvements. This "noise car" is a Ford Escape hybrid with a large contraption on the back bumper. Harvey says, "These are directional microphones. So the idea is to screen out everything but the noise coming from the tire-pavement interface."

You probably know the sound of the wooshing of a freeway. At high speeds, that noise is mostly coming from the pavement. "The tire is squeezing air out from under it continuously and that’s the hissing sound." The microphones on this car are just inches from the ground, so Harvey and his team can record newly designed quieter pavements, like sections of concrete installed on I-5 in Sacramento. "We’re designing the pavement so the surface is porous and the air can be squeezed out from the tire and actually squeezed down into the pavement and that drops the noise considerably."

Freeway noise is mostly controlled with sound walls in California, but Harvey says they’re often more expensive than building the road itself. Some next-generation pavements will also save money for consumers – since roads affect how much fuel a car uses. "You’re consuming energy in your shock absorber. And your tires are actually consuming energy. They’re interacting with the surface of the road." The bumpier the road, the more work your car has to do.

"When you smooth a road, you can get two to five percent improvement in fuel economy, depending on the current roughness." And since that affects all the cars on the road, Harvey says it’s a way to cut greenhouse gas emissions under California’s landmark climate change law. Cleaner car regulations will undoubtedly make up the bulk of those cuts, but Harvey hopes that pavement will also get its due.

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About the Author ()

Lauren is a radio reporter covering environment, water, and energy for KQED Science. As part of her day job, she has scaled Sierra Nevada peaks, run from charging elephant seals, and desperately tried to get her sea legs - all in pursuit of good radio. Her work has appeared on Marketplace, Living on Earth, and NPR's Morning Edition and All Things Considered. You can find her on Twitter at @lesommer.
  • Greg D

    Great work!

    I'm still astounded that it currently costs about $1M to build only a mile of highway. We need a road technology that only costs $100k per mile!

    • Carter

      You have to look at the cost over the life of the pavement. Even if you assume a conservative 25-year life for that mile of highway, the cost is well below your $100,000 per mile price point. With Perpetual Pavement designs, which with only periodic resurfacing should last for 70 years or more, the cost per mile drops even further.

  • Rpopoca

    MUCHAS FELICIDADES DESDE MEXICO BROTHER IN LAW MUCHO EXITO EN TUS PROYECTOS.

    RAMÓN.