Toward Adapting HDM-III Model to Local Conditions: Lessons from a Case Study in Tanzania

Abstract

Drawing from a case study in Tanzania, a generic approach to the problem of the desirability and scope of recalibrating the HDM-III model for local application is presented. On the basis of the three key factors of locational sensitivity, parameter impact on the model output, and the availability of calibration resources, candidate parameters for calibration are recommended for the case region. The roughness progression factor was found to have the highest impact on the net present value (NPV) of life-cycle costs. The roughness-age, cracking progression, and pathole progression factors were found to be the next influential on the NPV, with elasticity values of 0.7 to 0.8. From these results the study recommended a priority list in allocating recalibration efforts. The study findings suggest that calibration of rutting, cracking initiation, and raveling can be given low priority where resources are constrained. Considerations in choosing the appropriate vehicle operating cost (VOC) model for local conditions are highlighted. The Brazil set of VOC relationships is recommended for many applications; however, recalibration for these equations is highly desirable. Recent changes in automotive technology (with increased engine power, higher gross vehicle weights and payloads, improved fuel efficiency and tire technology, etc.) are raising the question of obsolescence of the Brazil VOC relationships. This issue may pose the most important challenge to the next evolution of HDM-III.