Construction crews work to repair a road in Houston damaged by heat on June 27, 2023. Roads were similarly damaged during a heat wave over the Fourth of July weekend this year.
Mark Felix/AFP/Getty Images
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Mark Felix/AFP/Getty Images
A heat wave scorched much of the eastern United States over the Fourth of July weekend, bringing extreme temperatures that buckled roads and snarled holiday traffic.
Nowhere was this more dramatic than on a concrete-surfaced section of Interstate 97 south of Baltimore, where one lane suddenly buckled, causing it to close. A city street in Chicago experienced similar, though less dramatic, pavement failure, and several state transportation departments warned motorists to watch for additional heat-related road damage.
Scientists say such heat waves are becoming more common and intense. Climate change is bringing more extreme temperatures and heavy rainfall. Both can contribute to widening and cracking of sidewalks, making roads temporarily impassable while awaiting costly repairs. The question is: are the country’s roads ready to meet the challenge of a warmer, wetter future?
Civil engineers say the answers are not entirely clear.
What is happening to the country’s roads?
Heat-related road failure occurs when moisture-weakened pavement heats up, expands, buckles and warps, especially if high temperatures persist for several days, according to Charles Marohn, founder and president of Strong Towns, a Minnesota-based nonprofit that advocates for more resilient and safe urban areas.
When water gets under the roadway, “it gets a little soft and instead of being hard, it starts to move a little,” Maron says. This weakens the pavement, and when it expands, it breaks.
“You take this long period of just extreme heat and a lot of traffic, and then something like this happens,” Charlie Gischlar, a spokesman for the Maryland Department of Transportation, said of the I-97 incident in Baltimore.
Amit Bhasin, a professor of civil, architectural and environmental engineering at the University of Texas at Austin, says this is usually a problem with concrete, also known as rigid, pavement. Steel reinforcement or expansion joints can be added between concrete panels to accommodate expansion, he said.
But as anyone who has driven on these highways can attest, the rhythmic sound of expansion joints built into the pavement can be annoying to motorists.
“You don’t want to provide too much because it will affect the ride quality,” says Bhasin, who is also director of the university’s Center for Transportation Research. But too little means “it’s expanding more than it’s designed for, so it’s going to sag.”
Asphalt, the sticky black substance used to cover many roads, works differently. “What you see is … ruts forming, especially in slow-moving areas,” he says. “It usually…looks like liquid on a hot summer afternoon.”
Maron says asphalt is typically less durable but easier to repair, while concrete has a longer lifespan before failing. But when concrete fails, he says, “everything deteriorates very quickly.”
What can be done?
While concrete highways typically cost more to build, they tend to last longer and require less maintenance over their lifetime, Bhasin said. Asphalt roads, on the other hand, are cheaper initially, but usually require more frequent repairs and resurfacing.
“Any time you design an asphalt or concrete mixture, you are designing it for a specific temperature range,” Maron says. “Extreme events expose the limits of these assumptions,” he says. Under normal conditions, the coating may work fine, but when the temperature goes outside the expected range, problems begin to appear.
For some roads, engineers say a stronger, more expensive asphalt mixture may be the solution. For paved roads, “if you are using reinforced steel, you have to consider different percentages of steel reinforcement,” says Bhasin. “If you are using joints, then perhaps (engineers could use) … slightly different spacing between joints … or change the size of the panels themselves.”
The biggest challenge is weather and climate data—or the lack thereof—but “if there is a trend that predicts different kinds of extreme event scenarios, then that should be included in the pavement design,” Bhasin says. “Engineers have figured it out and can design it. They just need to know where to start.”
According to him, anyone can design super-reliable roads. “We could be very conservative and say, ‘OK, let’s design for extreme events,'” he says. But the cost will be higher. “So you have to say, ‘I’ll be fine if 99% of the time it works and maybe 1% of the time the movement is broken.’
“In many ways, we’ve been designing our infrastructure for decades, if not centuries, for relatively milder temperatures,” Michael Chester, an engineering science professor at Arizona State University, told NPR. Everything is taken into account recently. “Now that temperatures are getting warmer, you’re starting to see the dynamics of these extreme events intensify, exceeding the design thresholds of these infrastructures and their specific assets.”
Chester says the country’s approach to infrastructure such as roads in the past “does not seem sufficient” for the future. What is needed is a turn. “And that will require us to innovate, which is what we are doing. This will require us to share this knowledge, which is what we are starting to do.”