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.
Phase I: (1) Collect and review relevant domestic and foreign literature; research findings; and information relative to profile measurement and characterization, reporting, and use of roughness data. This information may be obtained from published and unpublished reports, survey of state DOTs, and contacts with transportation agencies and other public and private organizations involved in profile measurement. (2) Based on the review performed in Task 1, identify current and emerging profile measurement technologies, and assess their capability for measuring accurate elevation profiles at low speeds (including stoppage) and in urban settings (e.g., signalized locations, crowned intersections, sudden grade changes, and unique surface features, traffic conditions, and road geometry). (3) Based on the review performed in Task 1, identify and evaluate available means for characterizing and reporting pavement roughness for project and network levels for the conditions noted in Task 2 and recommend potential means for further evaluation/development in Phase II. (4) Based on the evaluations performed in Tasks 2 and 3, prepare an updated, detailed work plan for Phase II that includes an approach for further evaluating the potential means identified in Task 3 and developing validated means for characterizing and reporting pavement roughness on low speed and urban roadways. (5) Prepare an interim report that documents the research performed in Tasks 1 through 4. Following review of the interim report by the NCHRP, the research team will be required to make a presentation to the project panel. Work on Phase II of the project will not begin until the interim report is approved and the Phase II work plan is authorized by the NCHRP. The decision on proceeding with Phase II will be based on the contractor’s documented justification of the updated work plan.
Phase II: (6) Execute the plan approved in Task 5, and develop and validate the means for characterizing and reporting pavement roughness of low speed and urban roadways. Also, describe how the pavement roughness data obtained from the developed method can be used as a measure of ride quality. (7) Recommend changes to current AASHTO standard practices to accommodate measuring, characterizing, and reporting pavement roughness on low speed and urban roadways for consideration and adoption by AASHTO, or develop new practices if necessary. Also, describe costs and benefits associated with the implementation of the new or revised practices. (8) Submit a final report that documents the entire research effort. The recommended changes to current AASHTO practices shall be prepared as a stand-alone deliverable suitable for consideration and adoption by AASHTO.
Status: Research in progress.