As the Earth's temperature rises and extreme heat waves become more common, all kinds of formerly rare and manageable issues are becoming bigger problems. One example: roads getting so hot they jump up from the Earth, or "buckle," causing delays at best and closures requiring major repairs at worst.
Just last week, buckling roads slowed or halted traffic in the Pacific Northwest. But it wasn't the first time; in 2019, when Seattle had a then-record heat wave, a driver suffered minor injuries when the road buckled underneath her. Also this month, the Minnesota Department of Transportation said it has responded to 43 "road explosions'' in the Twin Cities area during a recent heat wave. A spokeswoman for MNDOT called it "a traffic emergency."
But road buckling is just the beginning of the potential problems climate change will have on American roads. If we don't change the way we approach paving roads, greater temperature fluctuations with more extremes on either end of the scale will stress pavement and make maintaining roads more difficult, more expensive, and vulnerable to major flaws that cause delays, increase vehicle maintenance costs, reduce fuel or electric-propulsion efficiency, and generally make our infrastructure worse.
To address this, it will likely require re-evaluating what we make our roads out of, Joe Mahoney, Professor of Civil and Environmental Engineering at the University of Washington, told Motherboard: "If our climate is changing like this, and if we're going to have these heat domes and stuff, we're going to have to take a fresh look at some of those assumptions that are built into the infrastructure we've been building over the last many decades."
Unfortunately, he added, "there's no easy fix."
Generally speaking, there are two types of roads in the U.S.: concrete and asphalt. Concrete roads are made of slabs about 15 to 20 feet long. Concrete expands and contracts as the temperature changes, so road builders put some space in between each slab. These spaces are called joints—you likely know them from the bu-bum…bu-bum...bu-bum sound as you go over them on the highway—so the concrete has somewhere to expand as temperatures rise. Road buckling occurs when there is no more space in the joints for the concrete to expand and the pressure builds until the concrete, as Mahoney put it, "blows up."
The other major type of road surface, asphalt, is less prone to buckling, although you will occasionally see concrete roads with an asphalt layer on top also buckle. Asphalt is composed of small, ground up bits of sand, stone, and gravel with a hot liquid that binds them all together and then dries in place on the road during paving.
But asphalt has a different problem with temperature, according to Erdem Coleri, a professor of construction engineering at Oregon State University. Heat and cold will make asphalt harder, which makes it more likely to crack, or softer, in which case it will deform. These problems are less likely to need major emergency repairs, but can cause serious maintenance headaches over time. This is especially true for heat waves, because road paving happens in the warmer months, but if it is too hot out that first summer the asphalt is laid, the asphalt will not oxidize properly, making it more likely to have major deformations just months into what is typically assumed to be a decades-long life cycle.
The good news is there are options on the table for local authorities to make roads more resilient to extreme weather. The bad news is all of them involve trade-offs.
As Mahoney explained, climate is hardly the only consideration when deciding whether to pave a road with asphalt or concrete. For example, asphalt is much easier and cheaper to dig up in order to access utilities underground. But concrete will generally handle heavy loads better, so it might be a better choice for bus lanes or slow-trafficked city centers. Asphalt will also absorb a lot more heat than most concrete, exacerbating hot temperatures and creating heat islands in urban areas. And while the chemical composition of the binders in asphalt can be changed to work better in different temperatures, the wider the temperature range the road will experience, the harder it is to make a road that will be resilient in all seasons.
For example, Mahoney said in Saudi Arabia, which knows a thing or two about heat, the roads and highways are almost all asphalt. But while temperatures can get as low as the high 50s during winter nights in Riyadh, road pavers there don't have to worry about freezing rain, snow, or ice. Making roads that work for both extreme cold and extreme heat is, well, extremely difficult.
"There have been calculations done in the past that say, okay, this is going to work great for this climate," Mahoney said. "But if your climate's changing, then the game's changing."
In the long term, regions with concrete roads can add more joints, which gives the concrete more room to expand before buckling. This will increase construction costs by about five or ten percent, Mahoney estimated. But this is only something local and state authorities will do once roads are due for a resurfacing, which in some cases may be decades from now. In the meantime, he said, they will probably continue to just repair buckled roads as needed.
Coleri also suggested that, as far as asphalt goes, authorities consider designing new pavement compositions with future climate change in mind. But one of the big obstacles here is that, while state departments of transportation do a lot of research and consultation on asphalt composition, they are typically responsible for only a fraction of the state's roads. Most roads are maintained by city, town, or county governments, and their interest in such matters as pavement composition varies widely.
To get these local authorities to pay more attention to the issue, Coleri says it's important not to make it sound like everything about road-building has to change. "I'm not talking about a complete change in the design process," he said. "We just need to think about how to adapt, basically, by doing small changes in the current process. Because when you say 'change everything,' then people get discouraged. And I don't think we need to change everything. We just need to find solutions in order to adapt to this new situation."