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Photo by Patricia Lim/KUT

Extreme heat bakes Austin’s streets, making them warp and crack

Thursday, August 17, 2023 by Nathan Bernier, KUT

Austin roads are taking a beating this summer. An extended heat wave that could be the most severe on record is warping highways and cracking streets. But the pavement is shriveling so slowly, it can be hard to notice.

One of the most catastrophic – and fortunately, most rare – road failures blamed on heat is called buckling. That’s when road segments expand into each other and push up, creating dangerous speed bumps on the highway.

“When it gets really hot, especially when you have heat over many, many days or weeks as we’ve seen here lately, we usually see that at the pavement joints,” said Brad Wheelis, a Texas Department of Transportation spokesperson.

No buckling has been reported this summer on state highways in TxDOT’s 11-county Austin district. But it has happened at least three times this summer in the Houston area.

A buckled frontage road on I-10 in Houston. The surface of the road is gray. It looks almost like a small ramp has formed in the road. The sections of the road expanded into each other, forcing the surface higher in the middle.

Photo courtesy of TxDOT. Part of an on-ramp to Interstate 10 in Houston buckled in late July.

“We don’t see it a whole lot here in the Austin district,” Wheelis said. “But in years past, that has been an issue.”

Rutting and cracking

A more common problem, something you may have seen, is called rutting. That’s when the asphalt gets so hot, it actually softens. Heavy vehicles can push against the asphalt almost like play-dough, creating ripples in the pavement.

“Basically, if you’re driving down the road, you’ll see what might look like grooves or tire areas, a little dip,” Wheelis said. Rutting is most common at intersections or where the road turns.

An extreme example of rutting where the pavement has started to crack.

Photo courtesy of TxDOT. An extreme example of rutting, where the pavement has started to crack.

Rutting can be dangerous if the grooves pull your tires in a different direction. When it rains, the ruts fill up with water, increasing the odds of hydroplaning.

Major highways and busy roads are most susceptible to rutting, because they have the most traffic and the heaviest vehicles.

But side streets can also crisp up in the relentless heat.

“Definitely, there’s a huge impact of this extended heat on our pavement network,” said Veena Prabhakar, a pavement engineer with the city. “If you leave something out in the sun, it starts to dry up, and it tends to get brittle, and it cracks up.”

As the oils in the asphalt evaporate, streets turn from black to gray. Austin’s newly resurfaced roads are turning gray faster than they used to, leading to rougher rides and premature cracking.

“When that happens, water gets into our pavement structure, and water is the worst enemy of pavements,” Prabhakar said, because water causes the pavement to break down and slowly disintegrate.

A relatively newly resurfaced four lane divided road in North Austin

Photo by Patricia Lim/KUT. Austin’s newly resurfaced roads are turning from dark to gray faster than before due to the heat, city officials say.

Some parts of the city have it worse than others. In East Austin, a clay-heavy soil underneath the roads shrinks as it dries out in the heat. When it rains, the clay expands, causing even more cracks on the pavement.

In 2011, the most severe summer on record, Austin had “lots of pavement failures,” Prabhakar said. This year’s summer is expected to be even hotter.

“We have more needs on the pavement network than we can afford to pay for,” Prabhakar said. “It’s hard to quantify early on the long-term effects of climate change.”

Inflation and worsening roads pushed Austin’s preventive street maintenance budget 30 percent higher in the last three years to more than $30 million. Spending on street repair has remained relatively unchanged since 2020, at around $22 million a year.

But many of the city’s streets are still in rough shape.

Austin uses vehicle-mounted lasers to grade the quality of city streets on a scale of A to F. Most are in excellent to acceptable shape. But about 16 percent of Austin’s streets were graded D (moderately rough ride), and 10 percent were F (very rough ride).

Future innovations

Pavement researchers say many of the older asphalt formulations aren’t working as well in cities like Austin, where summers are becoming more intense. So, cities have to adapt to new climate realities.

“It’s not like tomorrow, all the roads are going to fail,” said Shane Underwood, a professor and pavement expert at North Carolina State University. “It’s that there’s going to be more disruption little by little. It’s like nickel-and-diming you to death.”

Austin is taking some measures to protect roads from the heat. On certain busy streets, special chemicals are being added to asphalt that makes the surface resistant to a wider range of temperatures. But those high-performance chemicals are expensive, and the city expects to need a lot more in the coming years.

On a smaller scale, Austin is experimenting with cooling pavement by spraying streets with a chemical that includes titanium dioxide. A $17,000 pilot project is being done on a short stretch of Meinardus Drive just southeast of Interstate 35 and Ben White Boulevard.

A distributor truck sprays a yellow-looking liquid on to a black asphalt street.

Photo courtesy of city of Austin. Crews apply a water-based emulsion with titanium dioxide to Meinardus Drive in November. University of Texas researchers say lightening the pavement reduced surface temperatures by 3 to 10 degrees.

Treating streets with the lighter-colored seal helped to reduce the asphalt temperature by up to 10 degrees, said Dev Niyogi, a University of Texas professor who directs the Texas Extreme Weather and Urban Sustainability Lab and was involved in the project.

But Niyogi isn’t just concerned about cooling roads. He’s also worried about the temperatures in the neighborhoods that surround them.

“The effects go far beyond what happens just on the road surface and quickly gets into communities,” he said.

“Think about the roads being the arteries and veins of a city,” he said. “When you have every bit of that road hotter than the surrounding parks or open streets, then you’re going to have a much warmer body, and that’s what is our city.”

Austin has applied for a federal grant to expand the cool-pavement pilot project. An award announcement is expected in September.

Even as the city works to combat the heat’s effect on its streets, the road network keeps expanding each year. The region’s high housing costs are driving development farther out, intensifying dependence on roads and cars.

All those vehicles are contributing to the problem, and it’s not just tailpipes and engine blocks blasting out heat.

Cars and trucks account for about a quarter of greenhouse gas emissions in the United States, trapping even more heat in the atmosphere and putting a bigger strain on the roads we rely on to get around.

This story was produced as part of the Austin Monitor’s reporting partnership with KUT.

The Austin Monitor’s work is made possible by donations from the community. Though our reporting covers donors from time to time, we are careful to keep business and editorial efforts separate while maintaining transparency. A complete list of donors is available here, and our code of ethics is explained here.

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