This research developed recommended guidelines for measuring longitudinal pavement profiles in order to compute the pavement's International Roughness Index (IRI) and/or Ride Number (RN). The guidelines are based on a determination of factors that affect profile measurements, the impact of these factors on repeatability and accuracy of IRI and RN measurement, and the determination of how and when these factors can be controlled.

Today, longitudinal pavement roughness is a major factor in the evaluation of pavement condition and remaining life. Pavement roughness measurement varies by intended use and by network or project, the latter being sometimes used to determine bonuses or penalties for paving contracts. This phenomenon has not always been the case. In 1978, NCHRP Report 228, "Calibration of Response-Type Road Roughness Measuring Systems" examined the sources of variability in roughness measurements from road meters and identified calibration procedures to compensate for each source so that measurements would be consistent and correctable between different systems. This research became the basis of IRI when the technology was applied to similar problems confronting the World Bank.

The University of Michigan Transport Research Institute in Ann Arbor, Michigan, was awarded the contract under NCHRP Project 10-47, "Guidelines for Longitudinal Pavement Profile Measurement." This research sought to explain the underlying cause of common profile measurement problems in order to assist agencies charged with measuring longitudinal profiles with maximizing the quality of their pavement management system's roughness estimates. Current road roughness standards focus on equipment design, ignoring other independent variables such as pavement shape, measurement environment, equipment operation, and driver and operator proficiency, all of which impact profile measurement and the resulting IRI and RN. The agency final report addresses these shortcomings by evaluating each of the profile measurement factors that affect the agreement between profilers and the accuracy, repeatability, and interpretation or meaning of measurements that affect profiler performance. Consequently, IRI and RN values can be calculated from more accurate input, resulting in a more realistic assessment of pavement profile condition. Results have been published in NCHRP Report 434, "Guidelines for Longitudinal Pavement Profile Measurement" and in NCHRP Research Results Digest 244, "Operational Guidelines for Longitudinal Pavement Profile Measurement."

Status: The project is complete.

Product Availability: A report and a research results digest have been published as NCHRP Report 434, "Guidelines for Longitudinal Pavement Profile Measurement" and Research Results Digest 244, "Operational Guidelines for Longitudinal Pavement Profile Measurement".