Transferring Alabama's Smoothness Specifications from PI-based to IRI-based

Abstract

Currently, Profilograph Index (PI) is deployed as the pavement smoothness evaluation index in the Alabama DOT’s smoothness specifications. The specifications set the incentive, full and disincentive payment levels to encourage the construction of smoother pavement. The problems of this index are the poor correlation between PI and the driving comfort, and its walking-speed operation, which makes it infeasible to keep track of pavement smoothness condition over time and traffic. With the development of inertial profilers, smoothness specifications based on International Roughness Index (IRI), which can accurately evaluate the driving quality right after construction up to rehabilitation needs, are expected to address these problems. An analysis was conducted on the profile database pooled from a range of Alabama asphalt concrete pavements and Quebec Portland cement concrete pavements. Correlations between PI and IRI were developed by several statistic methods. According to these relationships, the PI-based smoothness specifications were transferred to IRI-based smoothness specifications.