Extreme heat buckles highways as climate change pushes roads past design limits

• A Fourth of July heat wave buckled pavement on Interstate 97 south of Baltimore and a city street in Chicago, forcing lane closures as temperatures exceeded the design limits of roads built for a milder climate.
• Heat-related road failure occurs when pavement expands and warps after days of high temperatures and heavy traffic, civil engineers said.
• Charles Marohn, founder of Strong Towns, said prolonged heat can weaken pavement and lead to cracking and buckling where water has damaged the base.
• Mikhail Chester, a professor of engineering at Arizona State University, said the country’s infrastructure was designed for temperatures that are now being exceeded, requiring innovation and adaptation.

Engineers say stronger pavement possible but at higher cost

A heat wave that scorched much of the eastern United States over the Fourth of July weekend brought extreme temperatures that buckled roads, snarling holiday traffic and highlighting the vulnerability of infrastructure built for an earlier climate.

The most dramatic failure occurred on a stretch of concrete-paved Interstate 97 south of Baltimore, where one lane suddenly warped, forcing its closure. A city street in Chicago experienced a similar, though less dramatic, pavement failure. Several state departments of transportation warned motorists to watch for additional heat-related road damage, according to NPR.

Civil engineers said the failures are not isolated events but a symptom of a warming climate meeting infrastructure designed for a different range of temperatures.

“When water gets underneath a roadway, it’ll get a little bit squishy, and instead of being firm, it’ll start to move a little bit,” said Charles Marohn, founder and president of Strong Towns, a Minnesota-based nonprofit that advocates for more resilient urban areas, according to NPR. Once the pavement is weakened, prolonged heat causes it to expand and break.

“You take that prolonged period of just intense heat, a lot of traffic on top of it, and that’s when you have something like this happen,” said Charlie Gischlar, a spokesperson for the Maryland Department of Transportation, referring to the I-97 incident.

Amit Bhasin, a professor of civil, architectural and environmental engineering at the University of Texas at Austin and director of its Center for Transportation Research, said the buckling is typically a problem with concrete, also known as rigid pavement. To account for expansion, steel rebar or expansion joints between concrete panels can be added, he said. But too many joints affect ride quality; too few, and the concrete expands beyond what it is designed for and buckles.

Asphalt, used on many roads, behaves differently. “What you see is that ruts form, especially in slow-moving traffic areas,” Bhasin said. Under high heat, he said, it can become liquid-like.

Marohn said asphalt is typically less durable but easier to repair, while concrete has a longer service life before failing. But when concrete does fail, he said, “it goes really bad, really quick.”

Engineers said solutions exist but come with higher costs. Bhasin said more durable asphalt blends, different percentages of steel reinforcement, or adjusted joint spacing could make roads more heat-tolerant. He said engineers have the knowledge to design such roads but need better weather and climate data to know what to plan for, calling a lack of such data a gap.

“Anyone can design super-robust roads,” Bhasin said. “We could be very conservative and say, ‘OK, let’s design for extreme events.’” But the cost would be higher, he said, forcing the choice of accepting occasional disruptions in exchange for affordability.

Mikhail Chester, a professor of engineering at Arizona State University, told NPR’s All Things Considered that “in many ways, we’ve designed our infrastructures over decades, if not centuries, for temperatures that have been relatively milder.” Now, as temperatures rise, the dynamics of extremes are taking hold, exceeding the design thresholds of infrastructure assets, he said.

Chester said the past approach “doesn’t seem to be sufficient” for the future. “And that’s going to require us to innovate, which we are doing. It’s going to require us to share that knowledge, which we’re starting to do.”