ASTM E1926-08 (R2021) PDF Download

ASTM E1926-08 (R2021) is a standard practice that provides a mathematical procedure for computing the International Roughness Index (IRI) of roads from longitudinal profile measurements. The IRI is a quantitative estimate of pavement roughness and can be obtained using various instruments. It is a stable measure over time, as it is based on the concept of a true longitudinal profile rather than the characteristics of a specific instrument.

Roughness information, measured by the IRI, is useful for pavement management systems maintained by transportation agencies. The Federal Highway Administration (FHWA) specifies the IRI of the right wheel track as the measurement of road surface roughness for their Highway Performance Monitoring System (HPMS). Additionally, when profiles are measured for both traveled wheel tracks simultaneously, the Mean Roughness Index (MRI) is considered a better measure of road surface roughness. Note that the MRI scale is identical to the IRI scale.

The IRI can be interpreted as the output of an idealized response-type measuring system, where the physical vehicle and instrumentation are replaced by a mathematical model. It is also a useful calibration reference for response-type systems that estimate roughness by measuring vehicular response. Furthermore, the IRI can be seen as the average absolute slope of the profile, with mathematical filtering to modify the amplitudes associated with different wavelengths.

This standard practice is based on an algorithm developed in the International Road Roughness Experiment, which was sponsored by various institutions including the World Bank. The algorithm's details can be found in World Bank Technical Papers and Transportation Research Board papers. The goal of this standard is to provide a consistent and standardized method for computing and reporting road roughness estimates for highway pavements.