The change from PSR to IRI makes comparisons between pre-1993 pavement condition data and 1993 and later pavement condition data as published by FHWA in Highway Statistics and elsewhere more difficult. Since there is not a precise correspondence between PSR and IRI ratings, a pavement rated "good" using an estimated PSR rating might or might not also rate as "good" using a measured IRI rating. As a result, trend comparisons should be made with care.
Both PSR and IRI primarily represent ride quality or surface roughness which is just one indicator of pavement condition. Depending on which data are available, the FHWA uses estimated PSR ratings and measured IRI ratings as indicators of pavement condition for its aggregate analyses at the national level, as in the Conditions and Performance Report to Congress. Although ride quality is an important indicator for users of the system, other pavement distress information, such as cracking, rutting, and faulting, would be needed to develop overall objective measures of pavement condition and performance. States consider this broader array of factors in developing their pavement management systems and improvement programs.
The user of pavement rating data contained in Highway Statistics is advised to use care and diligence in drawing conclusions or inferences from either the PSR or M ratings so as not to either overstate or understate the true pavement condition as might be reflected by a broader array of indicators.