Structural Coefficients and Life-Cycle Cost

As transportation agencies search for relief from highly strained budgets, a recent study from National Center for Asphalt Technology (NCAT) shows that hot mix asphalt (HMA) pavements can be designed approximately 18.5% thinner using the 1993 AASHTO Design Guide for flexible pavements. This savings is the result of recalibrating the asphalt layer coefficient. The previously recommended layer coefficient, used by the Alabama Department of Transportation (ALDOT), of 0.44 comes from the AASHO Road Test, which took place near Ottawa, Illinois from 1958 to 1960. The recalibrated average layer coefficient of 0.54 was determined by utilizing performance and traffic data from test sections at the NCAT Test Track, and reflects advancements made in HMA materials and construction over the last 50 years. While the direct savings of 18.5% HMA thickness is obvious, the savings in initial construction and life cycle costs are not as straightforward. However, there will always be a savings in the initial cost and user delay costs because thinner pavements are cheaper to build and take less time to construct. The economic benefits of changing to the new layer coefficient will vary depending upon what layer coefficient an agency is currently using. A survey of state transportation agencies found that there is little consistency in the layer coefficients used across the nation. Many states use different coefficients for varying types of mix or use a different coefficient beyond a certain depth of HMA, while others use the same value regardless of mix type or depth. This inconsistency between the states does not seem to follow a particular trend (e.g., higher values in the southern portion of the country). The wide array of layer coefficients used across the nation suggests that this value needed to be revisited, and has lead many states toward implementing mechanistic-empirical design systems. This paper describes the recalibration efforts at the NCAT Test Track followed by a discussion of life-cycle costs related to using a new structural coefficient. Data from the survey of state agencies are also presented relative to the new NCAT findings and life-cycle cost analysis.

• Record URL:
  • https://doi.org/10.1061/41167(398)62
• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/isbn/9780784411674
• Supplemental Notes:
  • Copyright © 2011 ASCE
• Corporate Authors:

  American Society of Civil Engineers

  1801 Alexander Bell Drive
  Reston, VA  United States  20191-4400
• Authors:
  • Davis, Kendra P.
  • Timm, David H.
• Conference:
  • First Congress of Transportation and Development Institute (TDI)
  • Location: Chicago IL, United States
  • Date: 2011-3-13 to 2011-3-16
• Publication Date: 2011

Language

• English

Media Info

• Media Type: Digital/other
• Monograph Title: Transportation and Development Institute Congress 2011 : Integrated Transportation and Development for a Better Tomorrow

Subject/Index Terms

• TRT Terms: Asphalt pavements; Calibration; Coefficients; Costs; Field tests; Guidelines; Hot mix asphalt; Life cycle costing; Pavement design; Pavement layers; Paving; State departments of transportation
• Geographic Terms: Alabama
• Subject Areas: Finance; Highways; Maintenance and Preservation; Pavements; I22: Design of Pavements, Railways and Guideways; I23: Properties of Road Surfaces; I61: Equipment and Maintenance Methods;

Filing Info

• Accession Number: 01347229
• Record Type: Publication
• ISBN: 9780784411674
• Files: TRIS, ASCE
• Created Date: Aug 8 2011 2:10PM