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Publication Number: FHWA-HRT-06-121
Date: November 2006

Long-Term Pavement Performance (LTPP) Data Analysis Support: National Pooled Fund Study Tpf-5(013)

Chapter 12. Key Findings

An overview of the findings from the performance comparisons between the five climatic scenarios established for the study can be found in table 36. The “X” symbol indicates differences exist, and they are statistically significant at a 95-percent confidence.

Table 35. Summary of statistical comparisons.
Performance MeasureDeep-Freeze Wet RegionModerate-Freeze Wet RegionNo-Freeze Wet RegionDeep-Freeze Dry RegionModerate-Freeze Dry Region
Roughness (flexible)      
Fatigue/wheelpath cracking (flexible) XXXXX
Transverse cracking (flexible) XXXXX
Rut dept (flexible)  XX X
Roughness (rigid) X XX 
Longitudinal cracking (rigid) XXXXX
Transverse cracking (rigid) X X  
Faulting (rigid)    XX

Following is a list of descriptions of the significant differences noted in table 36:

It should be noted that the data in this study do not support the notion that deep frost penetration and multiple FTCs are mutually exclusive. Areas do exist with high freezing indices and large quantities of annual FTCs.

A review of information provided by participating SHAs and relevant literature regarding local adaptations to mitigate frost was performed. There was a large variation in typical cross sections for similar design situations, and no specific treatment was universally used to counter frost effects. Many States with frost penetration did required additional surfacing or the replacement of frost-susceptible soils with frost-free material. In addition, most of the States have adopted Superpave PG binder specifications and mix design procedures. This relatively recent development has to a large extent eliminated local adaptations to materials specifications and mix designs for HMA pavements.

Life cycle cost analysis was conducted using two different approaches. The first approach used initial construction costs that were consistent for each of the five climatic scenarios and were based on a standard roadway design. This resulted in equivalent uniform annual costs that were not significantly different between the regions. The second approach used initial construction costs that varied with the climatic scenario. The typical section for the deep- and moderate-freeze regions included additional frost-free material to represent the mitigation found in the review of SHA information. This cost analysis resulted in the no-freeze region having equivalent uniform annual costs that were lower than the other regions.

The models developed from this study can be used in pavement management system applications as well as to perform local calibration for the NCHRP 1-37A Guide.

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The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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