BACKGROUND: Pavement smoothness (or roughness) is used by state highway agencies for monitoring network condition and other purposes such as assessing construction quality and optimizing investments in preservation, rehabilitation, and reconstruction. States are also required to report the International Roughness Index (IRI) as an element of the federal Highway Performance Monitoring System (HPMS). IRI is not measured directly but it is calculated as the mechanical response of a generic quarter-car, traveling at 50 mph, to the elevation profile of the roadway. There are concerns about using current practices for estimating roughness of low-speed and urban roads. Urban roadways contain unique features such as drainage provisions, sudden grade changes, and crowned intersecting streets. These features are included in the elevation profile and interpreted as roughness. Also, because IRI calculation is based on the speed- and profile-dependent mechanical response, the calculated IRI at a slower speed will vary depending on the nature of the roadway elevation profile and the chosen speed. In addition, changes in travel speed and stops or near-stops can further distort, or even invalidate, the measured elevation profile. Because of the unique features of low-speed and urban roads, use of the current practices for estimating pavement roughness may yield inappropriate and misleading data. Research is needed to identify, or if necessary develop, means for appropriately measuring, characterizing, and reporting pavement roughness of these roads. These means will help highway agencies obtain reliable information for use in monitoring pavement performance, evaluating construction quality, planning and making investment decisions, and interpreting national data (especially the HPMS).
OBJECTIVE: The objective of this research is to identify/develop a means for measuring, characterizing, and reporting pavement roughness on low-speed and urban roads.
Status: Research is complete. The final deliverable has been published as NCHRP Research Report 914.