They're the bane of modern interstates and countryside roads alike: Potholes cost American drivers nearly $6.5 billion dollars in flat tires, blown shocks, and cracked rims in 2013, according to AAA. Save your car this beating by learning to recognize the early warning signs of developing potholes and how to get them fixed before they turn into sinkholes.
The advent of the modern American highway system came about in the mid 20th century after a rather embarrassing Department of Transportation publicity stunt saw a convoy of 72 vehicles average just 6 mph over a trip from DC to San Francisco. But while President Eisenhower's Interstate Highway system certainly improved the state of roadways at the time, America's roads are still pretty simple—typically just a slab of concrete or layer of asphalt over gravel, compressed earth, or other substrate.
Concrete is more often used for freeways and overpasses, as they can easily be formed into slabs and joined together. Asphalt, conversely, is more often used for longer stretches of ground-level road. This material uses bitumen, rather than concrete's cement, to hold together sand and crushed rock as the roadway. It also requires a layer of sealant to prevent water intrusion.
Potholes need two elements to be simultaneously present in order to form: Water and traffic. Water intrusion into asphalt, typically from an improper seal, first penetrates into the substrate below, loosening the underlying soil. Combined with the near constant rumble of vehicle tires overhead—especially the gigantic 18-wheeler cargo trucks that DoT engineers in Eisenhower's day never imagined—and the liquefied soil will start to erode. Without this solid base of soil to support it, the asphalt layer loses much of its structural integrity as countless vehicles roll over it.
In areas where the weather can dip into freezing temperatures, the problem is even worse. Water, snow, and ice will inundate the road, then freeze and expand (as water is wont to do) during the winter. This is enough to cause the pavement to crack and, once the weather warms up again, cause the underlying substrate to erode. It's a double whammy and the reason why potholes seem to pop up so abundantly after heavy winter storms.
You can actually see these potholes forming by looking for crocodile cracks—the pattern of cracks in an unsupported asphalt road that resemble the diamond patterning on the reptile's back. These cracks will soon grow into deeper seams allowing the individual chunks of roadway to grind against one another like little tectonic plates—until a car tire flicks them free of the group and forms the beginning of the pothole. Luckily, potholes don't generally get very deep, though they can easily get a couple feet wide on less maintained roads and can still wreck a suspension (or cause an outright wreck) if you're not driving attentively.
Image: Vadim Ratnikov
Depending on where the road is, its maintenance duties fall either to state and local authorities or to the Department of Transportation. The method of actually fixing potholes depends on the weather and traffic conditions. If, say, a nasty pothole opens up on a major freeway but the weather isn't favorable, road crews will usually apply a temporary patch of cold asphalt until they can get back with a semi-permanent fix. Semi-permanent repairs are more involved and require crews to reconstruct the edge of the pothole, as well as the substrate underneath, before pouring hot asphalt and smoothing it with the surrounding roadway.
There are a number of ways to do perform these repairs: The fastest and least secure method is the "throw and roll" where in a temporary patch is made by shoveling cold asphalt into a pothole then compressing it by driving a truck over the patch. This method is only suitable as an emergency fix as repeated applications can wind up costing as much as five times what a single semi-permanent patch would cost a county.
An alternative to a semi-permanent patch, known as spray injection, is quickly becoming popular given its massive cost savings over conventional methods. Rather than send a full crew out to stand around and watch one guy dig out the pothole, shovel in hot asphalt mix, and compact it, the spray injection method can be accomplished by a single driver and a specialized sprayer truck such as those patrolling Bedfordshire, UK, and New York City.
For as satisfying as throwing and rolling some cold asphalt in that pothole at the end of your driveway would be, road repairs are best left to the authorities. As such, if you notice a particularly bad pothole on your daily commute, most every city (or at least county) in the US has a hotline for reporting them. If the pothole is on a freeway or interstate, try your state's DoT first. If they can't help you, hit up your local municipality.
Top Image: keantian