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Mon February 20, 2012
Pounding Pavement In Search Of A Smoother Drive
A sweeping transportation bill being debated in Congress addresses how to prop up dwindling funds for the nation's aging highways. States with their own budget shortfalls are facing the same challenge. In California, researchers are trying to stretch those resources by developing next-generation pavements that are quieter and more fuel-efficient to drive on.
It's not hard to spot roads in bad shape, but there's a telltale sign of a street that can't be saved. "A pothole is when you put the electric paddles [to it]," according to John Harvey of the University of California Pavement Research Center. "The pavement is dead. You should never get to a pothole."
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. "Actually, I've had people threaten to kick me out of the car," he says.
The pavement testing facility where Harvey works is at the University of California, Davis. A huge mechanical arm is rolling a truck tire over a patch of asphalt. "It goes back and forth — we're probably looking at 20, 22,000 repetitions a day," Harvey says.
This machine simulates years of traffic in just weeks or months, which shows whether a pavement will last or fall apart. "There's all kind of cracks all over it, and that is a structural failure," Harvey says, referring to a rutted test patch nearby. Roads fail because of repeated stress from weather and heavy-duty vehicles. "We only really design for truck traffic," he says. "You don't even count the cars."
Of course, the hurdle to fixing roads is cost. In 2011, California's transportation agency estimated that it needed more than $7 billion to repair highways. With the state's budget troubles, it got $2 billion.
But there was a time when road funding was plentiful. The Federal Aid Highway Act of 1956 funded construction of the Interstate Highway System. 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 has led analysts to predict that the federal Highway Trust Fund will be bankrupt by 2014.
The good news is that because the country spends an estimated $100 billion a year on roads, even small improvements can make a big difference.
"This is a noise car," Harvey says, referring to a Ford Escape hybrid with microphones on the back tire, just inches from the ground. The researchers use the Escape to test some of the road improvements they develop. "So the idea is to screen out everything but the noise coming from the tire-pavement interface," Harvey explains.
You probably know the sound of whooshing on 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," Harvey says.
Harvey and his team use the car to record new, quieter concrete pavements, like an experimental section on a Sacramento freeway. "We're designing the pavement so the surface is porous and the air can be squeezed out from the tires down into the pavement, and that drops the noise considerably," he says.
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. "When you smooth a road, you can get 2 to 5 percent improvement in fuel economy," Harvey says.
According to Harvey, many cities and states are also doing preventive 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.