The Pothole Problem
HOST INTRO: Humans have been making roads for thousands of years. About 150 years ago, we settled on one technology for most of our streets: asphalt. But there’s a problem with asphalt — it’s not weather resistant. Harsh New York City winters leave roads battered, cracked and full of potholes every year. And the city pays hundreds of millions of dollars to repave those roads. Maggie Green asks engineers if there’s a better way to tackle this problem.
GREEN: Staten Island has a lot of potholes. Alyssa Foccillo (foh-SILL-oh) drives on the island every day, and she’s gotten pretty good at dodging them.
GREEN: Back in 2014, she learned that lesson the hard way. She was driving this same route home from a friend’s house and found herself winding down Arthur Kill Road on the west side of the island.
At the time I didn’t really know where I was going and I kind of got lost.
GREEN: Foccillo hit a pothole…hard. Her car started to swerve.
It was kind of like, scary, it moved in a certain way that I was like, oh my god, I have no control over the car.
GREEN: She skidded to a stop further up the road. She was okay, but her car wasn’t.The tire had popped and her car’s undercarriage was wrecked. Today, there’s a big patch in the road where she says the pothole was, and a new pothole just up the street.
GREEN: The year of her crash, New York had a particularly bad winter, and the city repaired over 400,000 potholes. Lucius Riccio (Rick-ee-oh) was a transportation commissioner in the 1980s, but today he’s an engineer and teaches at Columbia and New York University. Instead of just repaving potholes, Riccio says until recently, the city wasn’t looking hard enough at the underlying causes.
That’s like coming across three or 400,000 dead cows and being proud of the great job you did, burying them without ever asking the question, why are the 300 or 4 hundred thousand dead cows in the first place?
GREEN: But Riccio says asphalt is ultimately an engineering problem. It warps and morphs depending on its age and the outside temperature. And to make asphalt better, you have to look at its chemistry and physics. It’s made up of a binder, a kind of black tar, and aggregate–rocks and sand. And the way those components interact can make or break the asphalt mix. Jo Sias (SIGH-es) is an engineer at the University of New Hampshire. She says you can think of asphalt like Silly Putty.
When you first play with it, it’s stiffer. But then as you’re, you know, the heat from your hands warms it up, it gets softer. And if you put it in the freezer, um, it gets very brittle and you can actually just shatter it.
GREEN: And cycle that happens every year. Water seeps into the asphalt when it rains or snows, then freezes when the temperature drops. Once the temperature rises, the ice thaws, leaving behind an empty space for a pothole to form. But continually patching up potholes weakens the asphalt in the long term.
So it’s not just about, um, you know, when a pavement gets in bad shape just putting bandaids on it.
GREEN: Sias says asphalt itself is a more or less mature technology. There are minor chemical tweaks you can make to an asphalt mix to make it more temperature or age resistant, but ultimately, the secret is just to keep on paving roads.
If you don’t maintain them, you’re not going to get, the extent of the life as you could but you do have to spend the money to do the maintenance.
GREEN: But researchers are now exploring new technology for road surfaces that might keep potholes from forming in the first place. Huiming (HUY-ming) Yin is a professor in the civil engineering department at Columbia University. He’s like a mad scientist of asphalt.
I like to drive on the new asphalt pavement. I love asphalt. (laughter)
GREEN: His research lab is full of construction materials and test gear. On one wall is a machine that kind of looks like a giant microwave oven. It’s big enough to stress test asphalt by sending it through freezing and warming cycles.
We can put the asphalt inside, and then we can have the airflow, then can make the material change with the temperature and with the time.
GREEN: These days, his research focuses on self-heating and cooling roads.
We um, invent a structure I call a geothermal heat wheel.
GREEN: What he calls a geothermal heat wheel is a way of regulating temperature. Yin imagines a street built like the blood vessels under your skin that keep you warm–a system of pumps filled with a flowing liquid just under the street’s surface that can heat streets in the winter. In the summer, the liquid pulls heat away from the street’s surface, cooling down the road. That warmer liquid is then stored underground until the winter, when it’s pushed back up.
I can use the heat pump to heat up the liquid, for example, I heat up to 25 degrees Celsius and make the surface become warmer.
GREEN: Because the roads wouldn’t freeze in the winter, Yin’s heat wheel would make the streets last a lot longer. But the whole system would also be a lot more expensive, about 10 times as much as traditional asphalt by Yin’s estimate. Bob Mayer is the director of operations at the department of transportation. He says instead of replacing the whole system, the city is focusing on making the process as environmentally friendly as possible. One way is by recycling asphalt…
And producing asphalt at lower energy levels with less emissions.
GREEN: The city is focusing on repurposing older asphalt plants to be able to take old asphalt pulled from city streets and reintroduce it into a new mix. This way, the city doesn’t have to truck in new materials to make a brand new batch every time a street is resurfaced.
Which will basically make it more emissions friendly and be more energy efficient.
GREEN: Riccio, the former transportation commissioner, says it’s important to keep making environmentally conscious innovations…even if the process of maintaining roads stays the same.
Right now, the best way is resurfacing. It’s not cheap. It’s not glamorous, but it’s absolutely essential.
GREEN: At least for now, he says, the asphalt technology that we’ve had for 150 years is still the best we’ve got. Maggie Green, Columbia Radio News.