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Breakdown: Why pothole formation isn’t just a winter problem

Published: Aug. 13, 2021 at 9:33 AM CDT
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MEMPHIS, Tenn. (WMC) - Nothing interrupts a your commute more than the sudden klunk of passing over a pothole.

As we all know by now, with the I-40 bridge still out of commission, the only route over the Mississippi River in Memphis is the I-55 bridge.

And several reports from drivers came into the WMC newsroom this summer that a new pothole that formed on the right northbound lane of I-55 was causing tire blowouts.

But, wait a minute... Aren’t potholes the result of a harsh winter? While it’s true that the winter’s freeze-thaw cycles can lead to cracks and ruts in the roads, even subtropical areas that rarely experience freezing temperatures have notorious road repair problems too.

According to “Rough Roads Ahead,” a report from the American Association of State Highway and Transportation Officials, an industry trade group, more than 60 percent of streets and highways in Los Angeles, San Francisco, San Jose, Oakland and Honolulu provide a “poor quality ride.”

Potholes are a product of cracks, water, winter cold and the hot summer sun.

Roadways are constructed in layers. The top layer is designed to be water resistant and curved to drain water off the road and onto the shoulder.

However, high temperatures can cause roads to crack. These cracks then make an opening for summer rains, which can erode sub-surface asphalt layers and create “air gaps.”

Air gaps are like “bubbles” that burst as soon as the heavy pressure of a large vehicle rolls over them, causing them to these bubbles to implode, leaving behind a pothole, a rut, or a sag.

This graphic shows how most of the potholes drivers are experiencing in the metro areas have...
This graphic shows how most of the potholes drivers are experiencing in the metro areas have formed.(Texas Department of Transportation)

During winter, the cold nights the freeze the water, causing it to expand.

During a clear sky day, the sun warms the road which melts the underlying ice. The melted water can flow to a different section of the roadway.

When the ice melts, the pavement contracts and leaves gaps in the surface under the pavement, where again water can get in and be trapped. This freeze-thaw cycle will weaken the surface.

The infographic above explains the pothole formation process
The infographic above explains the pothole formation process(Virginia DOT)

Additionally, road surfaces develop cracks due to the stresses caused by traffic and because of the heating and cooling of the surface. During the day, the sun warms the roadway causing it to expand a small amount, while nighttime cooling causes the road to contract.

Traffic over the weak spot in the road causes the roadway material to break down, and when that broken-down material is removed by constant traffic, it creates a pothole.

We see many potholes develop in the early spring as that is when we get nighttime temperatures below freezing and daytime temperatures above freezing due to the longer daylight hours.

Early spring can be considered pothole season.

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