Abstract:
The Highway Development and Management Tool (HDM-4) is a powerful system for the
analysis of road management and investment alternatives and it is used to prepare road
investment programmes and to analyse road network strategies.
In this study, the HDM-4 tool is used to find the AADT thresholds based on traffic, subgrade
and climate for upgrading low volume roads to maximize economic benefits in Sri Lanka.
Several road sections were defined based on different possible traffic, subgrade and climatic
conditions for Gravel, Penetration Macadam (PM), Surface Dressed (SD), Portland Cement
Concrete (PCC) and Asphaltic Concrete (AC) pavement types. Altogether more than 120
sections were modelled in HDM-4. Level-1 calibration was done in HDM-4 to harmonize
with the Sri Lankan condition. Using HDM-4 strategy analysis, different rehabilitation and
improvement alternatives were analysed. Maintaining existing pavement considered as the
base case. Analysis was done for a 20-year period and optimized for maximum NPV.
The outcomes of the analysis EIRR was compared in tabular and graphical forms in order to
identify the AADT thresholds for traffic, subgrade and climate for upgrading each pavement
type. This shows that traffic volume and growth rate are significantly affected and whereas
the effect of climate and of subgrade condition are negligible.
Upgrading threshold of low volume road can be decided based on traffic volume in AADT
with a fair assessment of the number of heavy vehicles, traffic growth rate and climate
condition. According to the study, AADT ranges were defined to get maximum economic
benefit for different pavement types of low volume roads in Sri Lanka.
Furthermore it can be concluded that low volume roads (AADT less than 1000) in Sri Lanka
can use Gravel, PM or SD pavement type with proper maintenance and it is more economical
than upgrading to AC or PCC.
Keywords: HDM-4, Low volume roads, Pavement upgrading, Road maintenance
