Evaluation of the Correlation between Pavement Residual Life and International Roughness Index of Highway Flexible Pavements

Abstract

Pavement performance which is the foundation for pavement design, is the ability of a pavement to satisfactorily serve traffic over a period of time. Studies have shown that up to 40% of pavement quality is lost within the first 75% of pavement design life and if no maintenance is undertaken, another 40% of pavement quality can be lost within only 12% of pavement design life, implying a relatively high drop rate in road quality within a short period of time. According to the World Bank Policy study in 1988, $45 billion worth of road asset infrastructure was lost by developing countries, due to inadequate maintenance and monitoring, yet this could have been averted by periodic maintenance costing only some $12 billion. Similarly, UNRA reported that rapid deterioration of their road asset is increasing maintenance costs estimated at $21 million annually. With an increase in pavement road asset, the road authority will find it even more challenging in carrying out effective maintenance and monitoring with priority. As such, better means of monitoring roads, using deterioration models based on available data like roughness can be of importance to the road authority. Estimating residual life which is a measure of what is left of the pavement with respect to a predetermined pavement condition has posed challenges to road authorities. To address this problem, a novel functional method for estimating residual life using traffic and roughness progression is proposed by performing an evaluation of the correlation between residual life and IRI for highway pavements based on historical and field data collected from the Tororo-Lira Road (273km in length). Specifically, the study determined the magnitude and nature of deviation between designed and actual traffic loading; developed a correlation between residual life and IRI obtained from field measurements; assessed the reliability of the correlation developed. The correlation developed is useful in the decision-making strategies at a network level. It also provides a basis for reward determination for Output and Performance-based Road Contract (OPRC) contracting style. The methodology involved comparing designed and actual traffic loading, evaluating the developed correlations using Stata and Microsoft excel software and validating the correlation. The study showed that residual life is section specific and roughness is sensitive to traffic loading. It also established that roughness is increasing at an annual average rate of 2.9% to 10.4% and 1.7% to 23.1% for the LHS and RHS respectively. Reliability of the correlations was tested by comparing predicted with observed residual life values. The linearized correlations estimated residual life mathematically in form: lnRL=a-bIRI.