This report describes the findings and results of research conducted to determine (1) the effect of initial pavement smoothness on the future smoothness and future life of various pavement types, (2) the effect of smoothness specifications on initial pavement smoothness, (3) the cost-effectiveness of smoothness specifications (including incentives/disincentives), and (4) the most suitable types of smoothness measuring equipment and smoothness reporting indices for use in future smoothness specifications. Detailed analyses of comprehensive time-series smoothness data showed that initial pavement smoothness has a significant effect on the future smoothness of the pavement in 80% of new construction (both AC and PCC pavements) and in 70% of AC overlay construction. Furthermore, using two different analysis techniques, it was illustrated that added pavement life can be obtained by achieving higher levels of initial smoothness. Combined results of both roughness model and pavement failure analyses indicated at least a 9% increase in life corresponding to a 25% increase in smoothness from target profile index (PI) values of 7 and 5 in./mi (0.11 and 0.08 m/km) for concrete and asphalt pavements, respectively. Cost-effectiveness analyses conducted on several pavement families showed that the most cost-effective smoothness levels are considerably higher than what is typically used as the current target [PIs between 0 and 5 in./mi (0 and 0.08 m/km) versus PIs between 5 and 10 in./mi (0.08 and 0.16 m/km)]. Moreover, theoretical pay adjustment functions for the pavement families examined showed greater maximum incentive amounts and more punitive disincentive amounts than current pay adjustment functions. A detailed evaluation of smoothness-measuring equipment resulted in recommended requirements for measured profile wavelengths, sampling interval, distance accuracy, vertical elevation accuracy, and other considerations. Reviews of various smoothness indices, in terms of their ability to correlate with user response and other smoothness indices, resulted in the international roughness index (IRI) and the PI being ranked highest, followed closely by the Michigan DOT ride quality index, the Janoff ride number, and the Sayers ride number.

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  • Corporate Authors:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    ERES Consultants, Incorporated

    P.O. Box 1003
    Champaign, IL  United States  61820
  • Authors:
    • Smith, K L
    • Smith, K D
    • Evans, L D
    • Hoerner, T E
    • Darter, M I
    • Woodstrom, J H
  • Publication Date: 1997-3


  • English

Media Info

  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 567 p.
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00740750
  • Record Type: Publication
  • Report/Paper Numbers: NCHRP Project 1-31, Final Report
  • Files: TRIS, TRB
  • Created Date: Sep 26 1997 12:00AM