INTRODUCTION

The Long-Term Pavement Performance (LTPP) program, established in 1987, is a comprehensive 20-year study of in-service pavements using a series of rigorous long-term field experiments to monitor more than 2,400 asphalt and portland cement concrete (PCC) pavement test sections across the United States and Canada. The program's primary goal is to understand why some pavements outperform others. Knowledge of the factors contributing to good pavement performance is key to building and maintaining a cost-effective highway system.

LTPP has addressed topics ranging from traffic loading to pavement design, maintenance, and rehabilitation. Findings illustrate not only the immediate value of the LTPP database, but also its potential for improving pavement technology.

This document highlights some key findings from LTPP analysis studies completed between 2000 and 2003. A number of analysis projects have been conducted since the publication of the first volume in 2000, Key Findings from LTPP Analysis 1990-1999. In all, approximately 50 documents were reviewed, including LTPP research reports and National Cooperative Highway Research Program (NCHRP) projects using LTPP data. Most of these documents are available at the LTPP or NCHRP Web site. The goal of this report is to provide LTPP partners with information that can help them in their efforts to design, build, and maintain cost-effective and long-lasting pavements, by providing sections on:

• Site conditions.
• Structural features.
• Material characterization.
• Initial roughness.
• Pavement maintenance.
• Pavement rehabilitation.
• Local calibration of the 2002 Pavement Design Guide.

The LTPP program incorporates two major studies­the Specific Pavement Studies (SPS) and the General Pavement Studies (GPS). The primary goal of SPS experiments is to conduct detailed analysis of specific performance factors of newly constructed pavements and overlays. In contrast, the primary goal of GPS experiments is to analyze performance factors of existing pavements and overlays.

LTPP Program

SPS Experiments: Analyses of newly constructed pavements and overlays:

SPS-1       Study of Structural Factors for Flexible Pavements
SPS-2      Study of Structural Factors for Rigid Pavements
SPS-3      Preventive Maintenance Effectiveness of Flexible Pavements
SPS-4      Preventive Maintenance Effectiveness of Rigid Pavements
SPS-5      Rehabilitation of Asphalt Concrete (AC) Pavements
SPS-6      Rehabilitation of Jointed PCC Pavements
SPS-7      Bonded PCC Overlays of Concrete Pavements
SPS-8      Study of Environmental Effects in the Absence of Heavy Loads
SPS-9      Validation of Superpave Asphalt Specifications and Mix Design

GPS Experiments: Analyses of existing pavements and overlays:

GPS-1 AC on Granular Base
GPS-2 AC on Bound Base
GPS-3 Jointed Plain Concrete Pavements (JPCP)
GPS-4 Jointed Reinforced Concrete Pavements (JRCP)
GPS-5 Continuously Reinforced Concrete Pavements (CRCP)
GPS-6A Existing AC Overlays on AC Pavements
GPS-6B New AC Overlays on AC Pavements
GPS-7A Existing AC Overlays on PCC Pavements
GPS-7B New AC Overlays on PCC Pavements
GPS-9 Unbound PCC Overlays of PCC Pavements

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