Development Guidance

National Guidance

How do you develop a smoothness specification? AASHTO has recently developed some provisional standards to help states develop smoothness specifications. It should be noted, however, that these specifications are geared towards “Ride Quality” specifications using inertial profilers. These provisional standards cover:

• Profiling Equipment

  AASHTO MP11 Standard Equipment Specification for an Inertial Profiler

• Equipment Certification

  AASHTO PP49 Standard Practice for Certification of Inertial Profiling Systems

• Operation and Evaluation

  AASHTO PP50 Standard Practice for Operating Inertial profilers and Evaluating Pavement profiles

• Pavement Ride Quality

  AASHTO PP51 Standard Practice for A Pavement Ride Quality Specification When Measured using Inertial Profiling Systems

An Example of Advanced Smoothness Specification

The draft HMA Smoothness Specification (Section 401) from the FHWA Western Federal Lands Highway Division is the most advanced smoothness specification. This specification contains the following features:

• Use IRI as the smoothness index system (except for Type V or shorter pavement sections).
• Mandate contractors to comply with AASHTO smoothness specifications PP11 (profiling equipment), PP 49 (equipment certification), and PP 50 (operation and evaluation).
• Require a cross-correlation (available in the ProVAL software) value of 0.9 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 draft Western Federal Lands HMA smoothness specification here!