I’ve been meaning to write this article for a while thanks to living in a city that is full of holes. The Economist magazine beat me to publishing an article, however it did spur me to write as well.
My main concern over the years I have lived in Sydney and the surrounding countryside is that many potholes here are man made!. The word “pothole” comes from a Middle English word “pot” that describes a hole for mining or peat digging and then the “hole” was added when roads started to be sealed.
The Economist article reports that in the US, the American Automobile Association (AAA) has calculated that 16 million drivers have suffered damage to their cars in the past five years thanks to bouncing through potholes. The AAA estimates around $3 billion a year in repair bills! The article says that in India it is worse – more than 3,000 people die due to accidents involving potholes presumably not just car drivers but motorcycle and bicycle riders who are thrown off their machines.
Potholes are dangerous for all road users and urban holes can cause more serious injuries for the two wheeled travellers due to a higher volume of traffic. It amazes me that roads aren’t looked after properly – it has to be better for a country to have sound infrastructure.
Potholes typically form due to changing weather conditions and the volume of traffic that use the road. Local and city councils typically resurface a road once in a while but will fill a pothole with blobs of asphalt. The problem is that the materials used don’t bond properly, so guess what, they are at higher risk of being broken by heavy traffic and do so easily, causing the hole to reappear over time.
What I have seen in New South Wales is that when a road is resurfaced, the contractors don’t lift the height of the manhole covers that allow access to drains and other piping. What happens is that the cover becomes lower than the rest of the road causing a man-made pothole! Over several resurfacing events, the cover can get as low as several inches from the main surface. To make it worse, often a week or so after resurfacing, another agency will come and dig up the new surface and replace it with less material, causing another hole or trench that will remain for several more years.
The problem of fixing potholes correctly has attracted researchers in the US and Europe. The University of Minnesota has developed an idea to improve the repairs. As I described above, local councils typically use blobs of asphalt to fill the holes. These blobs are usually cold or lukewarm and therefore do not bond well or get into the crevasses of the pothole. The University has mixed ground iron ore with the asphalt and then used microwaves in a process called “ferromagnetic resonance” to heat the material. The hot material is now easier to push into gaps and around the edges of the hole by the workmen thus making the old and new materials “weld” together.
The Swiss have gone one better. They have also used an iron ore mixture but use a magnetic field to heat the new material. The hot material is then loose enough to find its way deep into the gaps, thus making a stronger bond that would fill the hole and last longer. The key here is that the road is resurfaced using the iron ore asphalt mix and then once a year or so, a mobile magnetic field is passed over the surface that heats and moves the material to smooth it out. This reduces the need for the lukewarm asphalt used today.
Other researchers are looking at how a local council could know that a pothole has appeared. Some ideas include mounting sensors or cameras to the underside of buses that can report that a crack or hole has appeared. The council can then schedule a fix – perhaps using an autonomous vehicle during the night when the road isn’t used.
Considering that so much money is spent on maintaining vehicles to be road-worthy, it is disappointing that roads aren’t kept vehicle-worthy, especially after the amount of tax road users pay to use them.