Development Guidance

National Guidance

How do you develop a smoothness specification? AASHTO has developed standards to help states develop smoothness specifications. It should be noted, however, that these specifications are geared towards “Ride Quality” specifications using inertial profilers. See the AASHTO Specification page for further details.

An Example of Advanced Smoothness Specification

The FHWA HMA Smoothness Specification (Section 401.16) is most advanced smoothness specification. This specification contains the following features:

• Use MRI as the smoothness index system.
• Mandate contractors to comply with ASTM E950 (profiling equipment) and R 56 (equipment certification) specifications.
• Require a cross-correlation (available in the ProVAL software) value of 0.90 between contractors' equipment and a government profiler.
• Mandate the use of the ProVAL for profile analysis.
• Define localized roughness using a report of continuous IRI with a base length of 25 feet (available in the ProVAL software).
• Use (fixed interval) IRI reports with a base length of 0.1 miles excluding non-overlaid cattle guards and bridges.
• For new or re-constructed pavements: compute pay factors based on the ProVAL's roughness histogram (based on the continuous IRI report from the Smoothness Assurance Module or SAM in ProVAL).
• For overlaid pavements: make use of a "percent improvement" table to determine pay factors.
• Allow grinding for defective area correction (with some limitations).
• Mandate the use of ProVAL's grinding simulation tool (in SAM) to minimize the amount of grinding needed to decrease the roughness to acceptable limits.

Download a copy of the FHWA HMA Smoothness Specification (Section 401.16) here!