Heat waves buckle roads across the U.S., raising questions about infrastructure costs and climate adaptation

A July Fourth weekend heat wave brought extreme temperatures to much of the eastern United States, causing pavement failures that snarled holiday traffic. The most prominent incident occurred on Interstate 97 south of Baltimore, where one lane of concrete pavement warped and was forced to close. Several state departments of transportation issued warnings to motorists about additional heat-related road damage.

Civil engineers interviewed by NPR described the mechanics of the failures. Charles Marohn, founder and president of Strong Towns, a Minnesota-based nonprofit focused on urban resilience, said that when water gets beneath a roadway it causes the surface to become "a little squishy," weakening the pavement before it expands and breaks under heat. Amit Bhasin, a professor of civil, architectural and environmental engineering at the University of Texas at Austin and director of the university's Center for Transportation Research, said the problem is more common in concrete — or "rigid" — pavement, which requires expansion joints or steel rebar to accommodate thermal expansion. Asphalt behaves differently, tending to form ruts in slow-moving traffic areas rather than buckling sharply.

Engineers described a cost and durability trade-off between the two pavement types. Concrete roads cost more to build but generally last longer and require less maintenance. Asphalt roads are less expensive upfront but need more frequent resurfacing. When concrete does fail, Marohn said, "it goes really bad, really quick." Potential engineering responses include denser steel reinforcement, adjusted joint spacing, or different panel sizes for concrete roads, and more durable — and more expensive — asphalt blends for flexible-pavement roads.