Vol. 1 No. 3
August 2, 1996


Federal Highway Administration
Office of highway Information Management

Use of Roughness Data as an Indicator of Pavement Condition

Beginning with data published in Highway Statistics 1993, the Federal Highway Administration (FHWA) began a transition to a new indicator of pavement condition based upon the International Roughness Index (IRI). The IRI is an objective measure of pavement roughness developed by the World Bank. When in full use by the States, [RI is expected to replace an earlier indicator of pavement condition, the Present Serviceability Rating (PSR). The PSR is generally recognized as a more subjective indicator of pavement condition because it is based upon human observation. The IRI was adopted as an indicator of pavement condition by FHWA because it uses a standard procedure that can be replicated; it is an objective measurement; it provides for consistent measurement across jurisdictions; and it is consistent with accepted worldwide pavement roughness measurement procedures.

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.

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