Distress Data Consolidation Final Report

BACKGROUND AND OBJECTIVES

Pavement distress data are among the most important measures of long-term performance. These data are especially important in the development of structural design methodologies and models to predict the occurrence of individual distresses. The Long-Term Pavement Performance (LTPP) program of the Strategic Highway Research Program (SHRP) recognized the importance of these data and established data collection guidelines and methods for monitoring the pavement performance.

Considerable resources have been expended since the LTPP program was initiated to ensure that changes in surface distress with time are adequately documented. As of October 1998, more than 7,000 distress surveys had been conducted on more than 2,000 LTPP test sections across North America, averaging more than three surveys per test section. Sufficient data are now available to begin examining trends in pavement performance.

Initially, photographic distress surveys were performed at each test section with manual distress surveys performed only on an as-needed basis. However, it quickly became apparent that photographic surveys did not capture all surface distresses. Accordingly, distress data collection efforts were revised in 1995 with much greater emphasis on manual surveys. Additionally, distress definitions and measurement techniques were revised in an attempt to improve consistency in data collection. As of October 1998, approximately 3,000 photographic and 4,400 manual surveys had been conducted.

Due to the inherent differences between photographic and manual survey methodologies, and because there had been revisions to distress definitions and data collection methodologies, variability of the condition survey data was a major concern. Therefore, the primary objective of this effort was to produce a comprehensive consolidated distress data set to reconcile differences between data collected using different methodologies. To develop this consolidated distress data set, considerable effort was directed toward identifying discrepancies in the distress data and establishing procedures to reconcile them. Hence, a secondary objective was to produce a set of guidelines to resolve the discrepancies encountered.

All distress data used in this study were released in version 8.6 of the LTPP database dated 1 October 1998 and have reached a Level E status, which indicates that the data have passed all quality control (QC) checks within LTPP to produce consistent and reliable information.

SCOPE OF REPORT

This report documents the review process used to identify discrepancies in the distress data and the recommended procedures to reconcile them. The report includes five chapters beyond this introductory chapter. Chapter 2 includes an overview of the graphical analysis used to identify outliers or discrepancies. Chapter 3 outlines the procedure used to categorize the discrepancies. A brief discussion of the software developed to automate the review process is included in chapter 4. Reconciling the discrepancies is addressed in chapter 5. Key findings are presented in chapter 6. Detailed listings of the discrepancies by section are included in the appendices.