An analysis is described that was undertaken with the objective of developing realistic models for estimating present serviceability index (PSI) as a function of international roughness index (IRI) for asphalt and concrete pavements. These models were developed by first analyzing the correlation between slope variance and PSI values obtained in the serviceability correlation analyses for the Road Test conducted by the American Association of State Highway Officials (AASHO) and then analyzing the correlation between slope variance and IRI for profiles representing a broad spectrum of road roughness levels. Equations are given for the recommended PSI-IRI models for asphalt pavements and concrete pavements, respectively. The Road Test data clearly demonstrate a difference between concrete pavement serviceability and asphalt serviceability for a given level of roughness as measured at the Road Test and quantified by the slope variance as defined at the Road Test. Whether this would be true for other roughness indices is impossible to conclude from the Road Test data. For the purpose of design and evaluation of pavements according to the AASHTO methodology, serviceability will be estimated erroneously as a function of IRI if this difference by pavement type is not taken into consideration.