ASTM E1926-08 (R2021) pdf free download.Standard Practice for Computing International Roughness Index of Roads from Longitudinal Profile Measurements.
1.1 This practice covers the mathematical processing of longitudinal profile measurements to produce a road roughness statistic called the International Roughness Index (IRI).
1.2 The intent is to provide a standard practice for computing and reporting an estimate of road roughness for highway pavements.
1.3 This practice is based on an algorithm developed in the International Road Roughness Experiment sponsored by a number of institutions including the World Bank and reported in Iwo World Bank Technical Papers (1, 2).2 Additional technical information is provided in two Transportation Research Board (TRB) papers (3, 4).
1.4 The values stated in SI units are to be regarded as the standard. The inch-pound units given in parentheses are for information only.
4. Summary of Practice
4.1 The practice presented here was developed specifically for estimating road roughness from longitudinal profile measurementS.
4.2 Longitudinal profile measurements for one wheel track arc transformed mathematically by a computer program and accumulated to obtain the IRI. The profile must be represented as a series of elevation values taken at constant intervals along the wheel track.
4.3 The IRI scale starts at zero for a road with no roughness and covers positive numbers that increase in proportion to roughness. Fig. I associated typical IRI values with verbal descriptors from World Bank Technical Paper No. 46 (2) for roads with bituminous pavement, and Fig. 2 shows similar associations for roads with earth or gravel surfaces.
5. Significance and Use
5.1 This practice provides a means for obtaining a quantitative estimate of a pavement property defined as roughness using longitudinal profile measuring equipment.
5.1.1 The IRI is portable in that it can he obtained from longitudinal profiles obtained with a variety of instruments.
5.1.2 The IRI is stable with time because true IRI is based on the concept of a true longitudinal profile, rather than the physical properties of a particular type of instrument.
5.2 Roughness information is a useful input to the pavement management systems (PMS) maintained by transportation agencies.
5.2.1 The IRI for the right wheel track is the measurement of road surface roughness specified by the Federal Highway Administration (FHWA) as the input to their Highway Performance Monitoring System (HPMS).
5.2.2 When profiles are measured simultaneously for both traveled wheel tracks, then the MRI is considered to be a better measure of road surface roughness than the IRI for either wheel track.
Note 1—the MRI scale is identical to the IRI scale.
5.3 IRI can be interpreted as the output of an idealized response-type measuring system (see Test Method E1082 and Specification E1215), where the physical vehicle and instrumentation are replaced with a mathematical model.ASTM E1926 pdf download.