Development of Guidelines and Specifications for Low Volume Sealed Roads through Back Analysis

The purpose of this Africa regional project is to develop guidelines and specifications for low volume sealed roads through ‘back analysis’, which is the analysis of historic performance data. Historically, low volume sealed roads (LVSR) were built using non-conventional standards and using materials that did not meet conventional specifications. This enabled significant reductions in construction costs and competitive life cycle costs when compared with the gravel road option. For the most part these roads have performed well, and many are now more than 20 years old.

Project Objectives

The aim of the project is to provide a consolidated knowledge base related to the performance of LVSRs using non-conventional design standards and materials through the provision of a database for the capture of data related to roads that have been 'back-analysed' over the past four decades in Sub-Saharan Africa.

The key objective is to undertake a review of the performance of existing LVSRs in order to:

1.     Provide a database of existing LVSRs that have been investigated related to pavement type and materials, performance and environmental conditions and consequently:

  • Refine existing generic guidelines for seal selection and pavement design based on whole life costs.

  • Corroborate and refine recent catalogues for pavement design for low volume sealed roads in order to ensure their applicability to a wider range of materials and geographic conditions.

2.     Provide a base level of information on the performance of non-standard designs and materials specifications when compared with traditional designs and specifications for roads carrying higher volumes of traffic (> 300 vpd).

The Low Volume Roads Database will be the first repository of its kind, containing data about LVSR sections on roads in Sub-Saharan Africa and South East Asia that was collected over a number of decades, and including aspects of their design, construction and maintenance that have influenced their in-service performance. The database will enable engineers and researchers to add new data collected from LVSR monitoring and use it to identify key factors associated with good or poor performance. Lessons learned from the database can then be used by recipient countries to update existing specifications or develop new documents to improve the quality of future LVSR design, construction and maintenance.

Methodology and Phasing

The project is designed in three phases:

Phase 1

  • Review previous studies identified by the project team and a pool of experts
  • Develop a database to store and interrogate data from previous studies spanning 40 years
  • Identify gaps in the knowledge base that can be investigated further in Phase 2.

Phase 2

  • Undertake field studies in four AfCAP countries covering approximately 30 road sections with a range of surfacing types, and in varying condition (good to poor)
  • Collect data on design and construction, maintenance interventions, historical traffic counts, rainfall and other road environment data in dry and wet seasons
  • Update the database with new data collected from the field.

Phase 3

  • Deliver a comprehensive knowledge exchange and dissemination programme
  • Use the outputs of this research to develop a set of regional guidelines and specifications for LVSRs.

Phase 1 of the project started in April 2016 and will run for 13 months.

Beneficiaries and Partner Countries

The main beneficiaries of the Regional Project on Back Analysis will be sub-Saharan African road and transport Ministries, Departments and Agencies, as well as Road Research Centres in the region and members of the African Road and Transport Research Forum (ARTREF). The database will also be available to practitioners in South and South East Asia, and already contains data from the South East Asian Community Access Programme (SEACAP).

BackAnalysis_TRL_DSC05235.jpgPhoto: TRL

Going forward, data collected by ReCAP on other AfCAP and AsCAP projects will also be included in the database, and the gap analysis and field investigations undertaken for these research studies will provide more evidence for incorporating the full range of LVSR construction and monitoring key performance factors into guidelines for surfacing seals.

The geographic areas and participating countries will be outlined in the Phase 1 Final Report that will set out the methodology and resource plan for Phases 2 and 3 of the project.

Project Resources and Reports

Back Analysis, Inception Report, June 2016

Back Analysis, Desk Study Report, November 2016

Back Analysis, Phase I Stakeholder Report - June 2017

Back Analysis, Final Report Phase I - May 2017

Back Analysis, Progress Report 1, March 2018

Back Analysis, Phase 2 Report, November 2018

Back Analysis, Phase 3 Inception Report, May 2019

Project Team Details

Andrew Otto (

Kenneth Mukura (