Science Behind Potholes

We are near the start of what is known as 'Pothole Season'. A season we know can wreck havoc. In fact in 2021, AAA found that 1 in 10 drivers sustained significant car damage that needed repair after hitting a pothole with an average cost per repair of $600.

In the most basic sense, potholes are caused by the weakening of asphalt. This occurs through the expansion and contraction of ground water within the pavement (often initially beneath the top road layer). If water freezes, it expands. If water melts, it contracts.

Think of an ice tray. After you place the water-filled tray in the freezer, the water expands upon turning into ice. This exact same process occurs in the asphalt when standing water is left to freeze. Slowly, the pavement weakens due to expanding, bending and the eventual cracking of the pavement.

Of course, the reverse is true when water melts. Upon melting, the pavement contracts which in effect leaves gaps and voids within the ground. These gaps can be exacerbated upon repeated freezes and thaws, most common as winter begins to transition into spring. It is this time of year that daily temperatures fluctuate most frequently between above and below freezing.

There is the additional variable of salt laid down on the road. Salt's role in the winter is to lower the temperature at which water freezes. This makes it more challenging for water to freeze, as the ground is being artificially warmed. Yet, if the temperature for which salt lowers the freezing point to is achieved, this freeze-thaw cycle repeats.

In colder locations, this can be more problematic because this freeze-thaw cycle can occur at say 20 degrees instead. Thus, road crews who are expected to fix these gaps endure harsher conditions to then try and repair them.

Now add in the weight of cars, buses or trucks and these weak spots in the pavement can cause surface material to be broken down over time. This in effect creates potholes, which can continue to be exacerbated unless filled.

Snowplows are another aggravate of an already weak pavement, as their blades can get caught and further pull apart the asphalt. However, proper blade height adjustment can alleviate most concerns.

In 2021, Clunker Junker, put out an article analyzing social media complaints to gauge where there are the biggest pothole problems. The team figured out the number of pothole-themed tweets over the course of the year and then collected the total road length in each state. Together, they were able to calculate the number of twitter pothole complaints per 1,000 km of road in each area.

The results? Well, they found Rhode Island to have the most with 23.4 pothole complaints per 1,000 km, and Idaho to have the least with 0.4 pothole complaints per 1,000 km. New York checked in at number 2, with 20.5 pothole complaints per 1,000 km.

When it comes to pothole remedies, most in the wintertime are temporary. One reason for this is because asphalt, which is needed to fill the potholes, has to stay hot and often will cool too much for usage en route to repairs. In fact, in many colder areas of the country, asphalt plants are shut down all together in the winter time for this very reason.

Furthermore, ideally for the asphalt to dry after repair, there needs to be little moisture interfering. Yet in the winter, moisture is ubiquitous, whether falling from the sky or simply just from melting snow or ice.

This is why the warmer and drier periods of late spring and throughout the summer are the most common for long lasting road repairs.