Road Note 31: A Guide to the Structural Design of Surfaced Roads in Tropical and Sub-tropical Regions (online edition)
Published: December 2022
Main topic: Access and infrastructure, Climate change, Roads, Adaptation
Study countrie(s): Sub-Saharan Africa, Low-and middle-income countries, Global, Africa
Written by: Alemgena Araya, Andrew Otto, Angella Lekea, Dr. Theuns Henning, H. Bailey, J. R. Cook, John Rolt, Manaye Ewunetu, Nigel Hewitt
Published by: TRL Ltd
Study type: Guide
This edition of Road Note 31 was developed through the High Volume Transport Programme (HVT), managed by DT Global UK. It has been funded by UK aid from the UK government; however, the views expressed do not necessarily reflect the UK government’s official policies.
Road Note 31 was first published in 1962 and revised in 1966, 1977 and 1993 to take account of advances in our understanding of the behaviour of road-building materials and their interactions in pavements. Many of these advances have been made by engineers and scientists working in tropical, sub-tropical and temperate climates; but a considerable amount of both fundamental and applied research has been necessary to adapt and develop the knowledge so that it can be used with confidence in tropical and sub-tropical regions. In addition to differences associated with climate and types of materials, problems occasionally arise in some countries from uncontrolled vehicle loading and unreliable road maintenance. At the same time, the level of technology and budget available for construction and maintenance can be relatively low. All this has presented a unique challenge to the highway engineer.
This edition of the Road Note has drawn on the experience of TRL, collaborating with experts and organisations in various parts of the world. It extends the designs of previous editions to cater for design traffic up to 80 million equivalent standard axles and takes into account the effects of climate and high axle loads. Rigid pavement design has been included in this new edition due to the importance of rigid pavements in combatting climate change.
Owing to the growing scarcity of natural gravels, foundation design principles have been included to encourage the use of various combinations of materials and allow for the use of recycled pavement materials within lower pavement layers. The range of structures has been expanded and the chapters on the different types of materials have been enlarged to provide more detailed advice on specifications and techniques. This includes materials such as Enrobé à Module Élevé (EME2 – High modulus asphalt), stone mastic asphalt and recycled pavement materials.
The rehabilitation of road pavements and economic analysis have also been included in this edition due to the importance of these two aspects of road provision in recent years.
Nevertheless, there will be situations and conditions that are not covered in this guide and there will be many examples where local knowledge can be used to refine and improve the recommendations.
