High Volume Transport

Vital transport research to ensure accessible, affordable and climate friendly transport for all.

Climate resilient road construction and Road Note 31 with Andrew Otto

In this episode of Reimagining Motion, we speak with Andrew Otto of TRL about the latest in road infrastructure research. How to build resilience to natural disasters and climate change into road design, as well as how to get policymakers on board. We also highlight specifically Road Note 31. The latest edition of the seminal guide for road construction in tropical and sub-tropical regions. Listen now wherever podcasts are found.

Below is an excerpt of the conversation, edited for length and clarity.

Holger Dalkmann

Tell us a little bit more what threat and problems climate change is having on our road infrastructure and what examples of this are we seeing?

Andrew Otto

Climate change is here and it’s possibly coming sooner than the infrastructure sector has been prepared for. Especially in tropical and subtropical countries. And the biggest change that is being noticed right now is the increase in rainfall intensity. And the disparity or the change at the of the intervals at which the rainfall now comes. For instance, an area that typically that used to receive two peaks of rainfall receive in a year, now receive one very high peak of rainfall and vice versa. Others that used to receive only one peak of rainfall in a year now can receive two or more and with very high intensity.

Now, as you can imagine, the effect that this would have on a structure such as a road pavement that is typically tied to the earth and it’s going to be affected. And when there are more cycles of wetting and drying, there’s going to be a change in its behaviour. And this actually manifests in deterioration of materials that are used in the road pavement, typically because of the increased intensity and the rainfall you have.

Also the increase in these temperatures means the bitumen or the asphalt roads tend to soften more easily under a load from trucks. And bear in mind that some of these trucks are actually very heavily loaded. If typically the maintenance or resurfacing cycle was, say, every 15 years now the resurfacing cycle will be shorter, it will be about ten years. So someone looking at their road today may say, oh, no, there’s absolutely no problem. Were they not realising that this effect is accumulating and suddenly you have it happening shorter time periods.


Can you give us a sense of all the other changes and challenges in recent years which need to be factored when a highway engineer in low and middle income countries consider the building and maintenance of roads.


Over recent years, there’s been several changes to the environment and the road designer or engineer has to take these into account. One of the most significant changes other than climate change is in the vehicle types that are now available in low and middle income countries.

The trucks that are now present on the network are much more powerful than those that were present over 30 years ago when we had the fourth edition of Road Note 31. We now have trucks that are capable of carrying much higher loads without actually feeling much stress in the engine. And as a result of this they tend to overload. And as you can imagine, and that causes a lot stress on the pavement as compared to when you have four tires.

The other major change over the years has been in the frequency by which this trucks and heavy vehicles use the roads. And because the numbers have increased, it means that in any vehicle stream. You’re likely going to find more heavily loaded vehicles or trucks within the stream. So from, say, previously having about 5% in the stream, we now talk of having 10% of vehicles in any traffic stream.


What else needs to be done? Is there enough awareness from agencies and policymakers? Do we have enough research? Where do you see the key elements of really scaling this issue and mainstreaming the issue of climate resilience and road building?


Now, the challenge is that there’s a lack of policy that contributes to a systematic approach. And sometimes climate resilient designs are sometimes expensive, compared to the standard designs. But on the flip side, there are also climate resilient designs that are actually cheaper than standard designs, and that the knowledge is in knowing when to apply and which technology where. And you can end up actually having more, much more cost effective options.