RENEE MONTAGNE, HOST:
And as Congress takes on a sweeping transportation bill, there's a question of how to prop up dwindling funds for the nation's aging highways. States with their own budget shortfalls are facing the same challenge. Researchers in California are trying to stretch those resources by developing next-generation pavements that are quieter and more fuel efficient to drive on.
From member station KQED, Lauren Sommer has this report.
LAUREN SOMMER, BYLINE: It's not hard to spot roads in bad shape, but there's a telltale sign of a road that can't be saved, according to John Harvey of the University of California Pavement Research Center.
DR. JOHN HARVEY: A pothole is when you put the electric paddles. The pavement is dead. You should never get to a pothole.
SOMMER: And filling them, he says, is only a temporary Band-Aid, lasting a year or less. Harvey is basically a pavement doctor. You can probably guess what he talks about on long car trips.
HARVEY: Actually I've had people threaten to kick me out of the car.
(SOUNDBITE OF TIRES ROLLING UP)
SOMMER: We're at the University of California, Davis pavement testing facility, where new highway materials take a beating. A huge mechanical arm is rolling a truck tire over a patch of asphalt.
HARVEY: It goes back and forth. We're probably looking at 20, 22,000 repetitions a day.
SOMMER: This machine simulates years of traffic in just weeks or months, which shows whether a pavement will last or fall apart, like a rutted test patch nearby.
HARVEY: There's all kind of cracks all over it and that is a structural failure.
SOMMER: Roads fail because of repeated stress from weather and heavy-duty vehicles.
HARVEY: We only really design for truck traffic. You don't even count the cars.
SOMMER: Of course, the hurdle to fixing roads is cost. In 2011, California's transportation agency estimated that it needed more than seven billion dollars to repair highways. With the state budget in trouble, it got $2 billion.
(SOUNDBITE OF NEWSREEL)
(SOUNDBITE OF MUSIC)
ANNOUNCER: In this century, America has become a nation on wheels.
SOMMER: But there was a time when road funding was plentiful.
(SOUNDBITE OF NEWSREEL)
(SOUNDBITE OF MUSIC)
ANNOUNCER: Congress responded with the Federal Aid Highway Act of 1956, providing the staggering sum of $51 billion.
SOMMER: Federal and state governments set up gas taxes to pay for road maintenance. But that revenue has 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.
The good news is - given that the country spends an estimated $100 billion a year on roads - even small improvements can make a big difference.
(SOUNDBITE OF CAR NOISE)
HARVEY: This is a noise car. So...
SOMMER: In a cavernous garage, Harvey shows me what they use to test some of those improvements. It's a Ford Escape Hybrid with microphones on the back tire, just inches from the ground.
HARVEY: So the idea is to screen out everything but the noise coming from the tire-pavement interface.
SOMMER: You probably know this sound - the whooshing of a freeway.
(SOUNDBITE OF FREEWAY NOISE)
SOMMER: At high speeds, that noise is mostly coming from the pavement.
HARVEY: The tire is squeezing air out from under it continuously and that's the hissing sound.
SOMMER: Harvey and his team use the car to record new quieter concrete pavements, like this experimental section on a Sacramento freeway.
HARVEY: We're designing the pavement so that the surface is porous and the air can be squeezed out from the tires down into the pavement and that drops the noise considerably.
SOMMER: That's a plus for communities next to freeways. It could also reduce the need for sound walls, which Harvey says are often more expensive than building the road itself. Some next-generation pavements will also save money for consumers, since roads affect how much fuel your car uses. The bumpier the road, the more work your car has to do.
HARVEY: When you smooth a road, you can get 2 to 5 percent improvement in fuel economy.
SOMMER: Harvey says many cities and states are also doing preventative maintenance on their roads before bigger problems like potholes emerge. That's more expensive, but it goes a long way toward increasing the life of a road.
SOMMER: For NPR News, I'm Lauren Sommer in San Francisco.