High Volume Transport

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How can we make road infrastructure more resilient?

Spotlight on Road Note 31

Road Note 31 draws on best practice from around the world to focus on the impact of climate change on roads in low-income countries.

A new, fifth edition of Road Note 31 (RN31) from TRL, funded by HVT, has been welcomed by stakeholders and transport policy makers across the global south as a reliable and effective tool for road design and construction. The Road Note, first published in 1962, has expanded across four earlier editions, providing valuable advice and information on a wide range of issues from design and maintenance of road surfaces to road safety concerns. The last, fourth, edition formed the basis of road manuals around the globe.

Team Leader at TRL, Andrew Otto, explained in a recent conversation why and how the Road Note has changed saying:

“In road engineering and science, knowledge is ever evolving. Sometimes to the extent that it completely changes the way we understand the behaviour of something or how things are best done. This was the case for RN 31. It had been last updated by TRL in 1993,  almost 30 years ago. A lot of knowledge and new materials have since come along, and this needed to be included in RN 31, a document that has shaped road design in low and middle-income countries (LMICs) in tropical and sub-tropical regions. It was important that LMICs had access to these new developments in the context of tropics and sub-tropics.”

A major area of concern addressed in the new edition is the climate resilience of transport infrastructure.

“The most critical challenges facing today’s infrastructure are climate change effects on already existing infrastructure which is not designed to withstand theses effects. Climate change affects coastal roads and also inland roads by deformation of the surfaces either from temperature or rainfall, destruction of bridges and road embankments and other forms of infrastructure,“ Andrew said.

“The RN 31 has incorporated design methods to promote the resilience of road pavements against climatic changes such as rise in temperature, extreme storm events and gradual annual increases in rainfall. Several pavement options and modifications are presented in the RN 31 to particularly address this,” he went on to say.

Road performance data was gathered from tropical and sub-tropical countries including Mozambique, Brazil, Zambia, Uganda, Vietnam and Mexico. As a result, knowledge of the adverse effects of climate impacts, and methods of minimizing them, have improved considerably.

Environmental degradation through direct emissions, tyre degradation and release of contaminants which end up in rivers and streams is another challenge addressed by RN31, along with traffic and truck characteristics which have damaging effects on roads. Most notable among these is the use of super singles, or trucks which have two tyres per load-carrying axle, rather than the traditional four.

Reacting to these challenges, RN31 fifth edition includes guidance on the design of concrete pavements to help with climate resilience and increased axle loads. It also addresses road/pavement rehabilitation and the use of climate resilient surfaces with enhanced road drainage.

The new guide also includes added emphasis on designs for rut resistance, since temperature rises, along with heavier traffic loads, lead to more frequent and severe rutting. And it provides guidance on the use of epoxy-modified road surfacings and chip seals which offer greater resistance to extreme temperatures, resistance to oxidation and are less susceptible to moisture permeation.

To tackle the effects of higher rainfall, this edition offers options and guidance including the use of filter materials and geotextiles. Extreme storm events causing washouts of roads are also addressed, with graphs and diagrams explaining ways to combat their destructive effects.

Talking further about challeges the updated Road Note needed to address, Andrew says: “The other aspect that cannot be ignored is the rising cost of infrastructure provision.”

“In terms of cost, the long-life pavement principles will go a long way towards curbing rising road provision costs. With advances in technology and investments in long-term research, other methods of solving these challenges can be developed.”

The guide is not country specific. In fact, it can be used in conjunction with most country design manuals because it complements and supplements those manuals. It can also be used on its own. However, it is for tropical and sub-tropical regions.

“The key feature of this Road Note 31 is its flexibility, which you will notice when you start using it,” said Andrew, of the guide, which provides a benchmark for empirical design. It is hosted on a website which allows users to give feedback. This will be gathered and used for future editions.

The updated Road Note 31 can be downloaded from the HVT website here.

There is also an interactive website here where users can access the most up to date version  incorporating any minor changes that may be made to the document in the next two years. The site also has other useful tools to assist users. Users can provide feedback through this site.

A number of printed copies of the fifth edition will be distributed whenever TRL visit FCDO partner countries.