Best practices for pavement smoothness specifications released

Austin, Texas — The Louisiana Transportation Research Center (LTRC) released a report summarizing current U.S. asphalt and concrete pavement smoothness requirements. The report, Best Practices for Achieving and Measuring Pavement Smoothness, A Synthesis of State-of-Practice, provides timely information as the U.S. undergoes a major shift in the way smoothness specifications are written. A growing number of states are moving away from profilograph-based smoothness specifications in favor of specifications based on a more widely accepted and precise measure of pavement smoothness: the International Roughness Index (IRI). LTRC’s report will help contractors, agencies, and engineers adjust to the change.

Smooth pavements provide significant benefits to the public and agencies. Smoother pavements can lead to increased public satisfaction with the road system, a reduction in fuel consumption, and longer-lasting pavements. U.S. state departments of transportation (DOTs) prescribe certain levels of smoothness in pavement specifications and often penalize or provide bonuses to contractors depending on the smoothness they provide.

Agencies are switching to IRI in order to more accurately assess the smoothness of their roads. IRI is calculated using a mathematical model to provide a “true profile” of the pavement’s actual cross section — it is a clearer picture of the road’s smoothness. IRI is reproducible and comparable across the world. However, limited knowledge of IRI can cause confusion during specification development or pavement construction.

LTRC’s report, written by pavement engineering firm The Transtec Group, summarizes the state-of-practice for U.S. state DOT pavement smoothness specifications based on IRI. Authors David K. Merritt, P.E.; George K. Chang, P.E., Ph.D.; and Jennifer L. Rutledge provide a summary of best construction practices for achieving required pavement smoothness, current smoothness specifications, IRI collection and processing technology, construction acceptance, current research, and educational and training practices.

Seventy-eight percent of U.S. state asphalt pavement specifications and 46 percent of concrete pavement specifications are currently based on IRI. As more states move towards IRI-based specifications, these numbers are expected to continue growing.

Download the LTRC pavement smoothness report at www.ltrc.lsu.edu/pdf/2015/FR_550.pdf.