Report: Roughness Index succeeding profilograph in pavement parameters

17 Report 400

“Best Practices for Achieving and Measuring Pavement Smoothness, A Synthesis of State-of-Practice” authors present state department of transportation adoption of International Roughness Index (IRI) versus profilograph-based index (PrI) pavement smoothness specifications.

A new Louisiana Transportation Research Center (LTRC) report tracks a major transition in current U.S. concrete and asphalt pavement smoothness requirements. “Best Practices for Achieving and Measuring Pavement Smoothness, A Synthesis of State-of-Practice” shows a growing number of states moving away from profilograph-based specifications in favor of those determined on a more widely-accepted and precise measure: the International Roughness Index (IRI).

Prepared for the 12-state Southeast Transportation Consortium with Federal Highway Administration cooperation, the LTRC report will help contractors, agencies, and engineers adjust to the evolving specs. Smooth pavements provide significant benefits to the public and agencies, authors contend, and can lead to increased road system user satisfaction, reduced fuel consumption, and longer-lasting thoroughfares. State departments of transportation prescribe certain smoothness levels in specifications, and often penalize or provide bonuses to contractors depending on finished pavement characteristics.

The report finds 46 percent of concrete and 78 percent of asphalt pavement specifications based on IRI. Agencies are switching to IRI in order to more accurately assess road smoothness. IRI is calculated using a mathematical model to provide a “true profile” of the pavement’s actual cross section and, proponents note, is a clearer picture of smoothness. IRI is reproducible and comparable across the world, although limited knowledge of the practice can cause confusion during specification development or pavement construction.

Prepared by Austin, Texas, pavement engineer and consultant firm The Transtec Group Inc., the LTRC report summarizes state DOTs’ IRI-based pavement smoothness specifications. Authors David Merritt, P.E., George Chang, P.E., Ph.D., and Jennifer Rutledge examine best construction practices for achieving required pavement smoothness, current specifications, IRI collection and processing technology, construction acceptance, current research, and educational and training practices. The report is posted at Additional information on pavement engineering and practice can be obtained from The Transtec Group,