Environmental Talk: What has Spilling Petroleum Products got to do with our Potholes?
A driver slows down to negotiate past a pothole in Kampala.

Environmental Talk: What has Spilling Petroleum Products got to do with our Potholes?


A thin, slippery film of spilled diesel stays around after a spillage but becomes invisible to the eye.

By Ivan Kibuka-Kiguli
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First published: December 3, 2007


Potholes on Ugandan roads - we all know and loathe them. When their sizes approach crater proportions, we start asking the Ministry of Works and Transport or the local authorities what they are doing about them. However, do we know what really causes them?


Most potholes are formed due to fatigue in the road surface. According to Wikipidea, in materials science, fatigue is the progressive and localised structural damage that occurs when a material (in this case tarmac) is subjected to cyclic (repetitive) loading. There is a variety of ways in which potholes can develop on our roads. Even to a non-engineering professional, some of these are more obvious than others.

We are all aware that the more advanced the age of a road, the poorer and weaker its surface becomes. Shoddy road construction methods and materials used by some contractors have also been mentioned to explain why some relatively new road surfaces develop potholes. When floods or sustained excessive ground moisture come along, even well constructed and maintained roads break up.

It is also common for vehicular traffic that is joining a paved road from a dirt/murram side road or shoulder to break stone chips off the edge of a road surface. Most Ugandan highways have soft and unprotected shoulders. The wheels of heavily overloaded trucks have been known to scrape stone chips off paved roads, especially when they attempt to execute sharp turns at low speeds. The scraped area, after seeing some more wear and tear from traffic, grows into yet another pothole.

However, there is another source of potholes that we often overlook - spillage of petroleum products on tarmac surfaces. If you have witnessed contractors lay tarmac/asphalt, you will be aware that they use bitumen in copious amounts. Bitumen is produced from crude oil via fractional distillation. Bitumen is what is left after the likes of jet fuel, kerosene, petrol, diesel, etc have evaporated out of crude oil. You may therefore say that bitumen and petrol/diesel are birds of a feather they belong to the same family of chemicals.

You may also have noticed that newly constructed/renovated roads have signs (for some reason, new road signs in Uganda always disappear after a while) reading, "Do not spill petroleum products on the road". This is for very good reasons. When you do spill petroleum products on to the road, some drain away into surrounding water streams and soil. We all know this is environmentally harmful.


Ugandan drivers deal with potholes on a very regular basis
Ugandan drivers deal with potholes on a very regular basis.

Whatever spilled petroleum does not drain away or evaporate off (causing yet more environment damage to the air we breathe) causes slippery conditions on the road surface. Petrol usually evaporates fast. Engine oil does not, but can be seen. Diesel on the other hand, has killed/injured many a cyclist without them knowing it. A thin, slippery film of spilled diesel stays around after spillage but becomes invisible to the eye. It is possible even for a pedestrian to slip on such a surface and wonder what caused it!

Remembering that the petroleum products we use in our vehicles share similarities in chemical constitution to bitumen, another danger in spilling these products on the road now becomes apparent. These oily substances can dissolve the bitumen that holds the stone chips together, leaving the chips free to be thrown about and away by traffic. You have just got yourself a pothole!

So, next time a vehicle breaks down by the roadside and you notice mechanics washing the mechanical parts of this vehicle with diesel/petrol and spilling it on to the road surface beneath, have a word with them and explain that it is their suspension that will break next time they drive past. Equally, we should all be vigilant and ensure we dispose of petroleum products safely. There are so many ways these substances are a menace to us.

By Ivan Kibuka-Kiguli
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First published: December 3, 2007
The author is a pollution control equipment engineer/consultant and a proud active member of UGPulse.