Extreme weather creates future potholes. Compounding this is how roads in the South might suffer more because the asphalt formulations are made for heat.
The Christmas week arctic blast – bomb cyclone Elliott, as it was called – across the entire midsection and East Coast of the US played havoc on transportation in many ways. Flight cancellations and advisories to stay off the roads were among them. But the deep freezing temperatures, in the negative (below zero degrees Fahrenheit) numbers, will probably have a long-term impact – from the Dakotas to Texas and Florida to Maine – due to damage to asphalt pavement.
The idea that winter conditions are what cause many if not most potholes isn’t new. Particularly when temperatures cycle above and below 32ºF, a process known as the freeze-thaw cycle, moisture invades small cracks and then expands (when frozen) to make those cracks bigger. That ultimately leads to bigger cracks, undermining pavement and causing the craters that inflict flat tires, damaged suspension systems, and sometimes deadly accidents.
But another problem arises as unusually frigid arctic air reaches further south. This is because road building varies a bit depending on the prevailing climate. In other words, the highways of North Dakota and Minnesota aren’t exactly like those of Texas and Louisiana. The variations are intended to account for warmer summer temperatures and a greater number of days of sunshine in those Southern states, as well as the deep freeze temperatures more typical of the northern Plains states.
“We’re building roads to withstand last century’s climate”
“The problem comes down to asphalt, which is a temperature-sensitive surface,” wrote John Timmer in arstechnica, a science, technology, automotive, and policy publication. His article, “We’re building roads to withstand last century’s climate” was published in 2017, alleging that “asphalt in use tolerates the temperature extremes of a period that ended in 1995 … It can crack if it gets too cold or undergoes freeze/thaw cycles, and it can partially melt if temperatures get high enough.”
“Of the roads built over the past 20 years, a full 35 percent were produced using an incorrect material,” the article continues. “In most cases, this involves a tolerance for cold temperatures that no longer occur. But in a quarter of these cases, the road was experiencing high temperatures that it wasn’t designed to tolerate.”
In other words, the design and construction of pavement has yet to be adapted to such things as bomb cyclones that bring record low temperatures in the South, as well as blistering summer temperatures when they reach farther north. In December 2022, places such as Tulsa, Oklahoma experienced a record low of -9ºF – this was while water systems in Shreveport (Louisiana), Selma (Alabama), and Greenville (South Carolina) froze. In Georgia, Atlanta’s 911 system was overwhelmed with calls about broken pipes in homes and businesses.
And in the Pacific Northwest, typically known for its moderate weather, the past two summers have experienced the opposite phenomenon: record high heat. The thermometer showed 120°F at Hanford, Washington, on June 29, 2021. On July 31, 2022, Portland, Oregon hit 116ºF, its all-time high, about a year after Seattle reached its record high of 108ºF on June 28, 2021.
A delayed awareness of how cold affects pavement
With broken pipes, cancelled flights by the thousands, and scores of deaths due to the storm, the effects on pavement might not be noticed until weeks and months into the future. Perhaps then departments of transportations in cities and states of the affected regions will tally the damage to pavement to identify how to plan for future events.
“There are different formulations, however,” writes Timmer. “So the starting material can sometimes be tailored to tolerate the temperatures it is likely to face. Engineering best practices involve figuring out the likely high and low temperatures a region is likely to face and choosing an asphalt blend that is rated to tolerate those.”
In other words, “temperatures a region is likely to face” is due rethinking by road engineers.
Meanwhile, in 2023, the millions of already-built roads need to be repaired and maintained. As potholes inevitably pop up later this winter and in the spring, they’ll likely (at best) get one of two treatments: a “throw-and-go” cold asphalt material, which is a temporary repair method, or a specialized material designed to ensure permanent repair. Throw-and-go is a lower-cost material, but labor costs incurred by repairing the same pothole a second time, in warmer weather, may make that method more expensive in total.