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Publication Number: FHWA-RD-06-067
Date: March 2006

Guidelines for The Collection of Long-Term Pavement Performance Data

Chapter 1. Introduction

1.1 Introduction to LTPP

Faced with the need for a better understanding of the parameters affecting pavement performance, the pavement community mounted an organized, massive, and multiyear project to study the effects on pavement performance of diverse environmental conditions, traffic, materials, pavement designs, construction techniques and quality control, maintenance strategies, and other important parameters. During the 1980s, the Transportation Research Board (TRB), along with the Federal Highway Administration (FHWA) and with the cooperation and support of the American Association of State Highway and Transportation Officials (AASHTO), began the Strategic Transportation Research Study (STRS) of the deterioration of the Nation's highway and bridge infrastructure system. The results of this study were published in TRB Special Report 202, "America's Highways, Accelerating the Search for Innovation." One of the primary recommendations from the study was the long-term monitoring of inservice highways. As a result of their recognition of the need for a national database containing long-term data from highway monitoring, the major agencies involved in pavement design, construction, and management joined together to develop plans for a Long-Term Pavement Performance (LTPP) study.

AASHTO approved the recommendations of the STRS and established the Strategic Highway Research Program (SHRP) to carry them out. As the result of the enthusiasm for this program expressed at a national workshop on long-term pavement monitoring sponsored by FHWA in October 1984, FHWA offered to fund transition activities to maintain the momentum until SHRP was approved by the U.S. Congress and funded in its own right. A SHRP Advisory Committee for Pavement Performance was appointed to provide guidance for this transition planning, including experiment designs and implementation planning.

1.2 Objectives of LTPP

The objective of the LTPP program adopted by the Advisory Committee for Pavement Performance was:

"To increase pavement life by investigation of various designs of pavement structures and rehabilitated pavement structures, using different materials and under different loads, environments, subgrade soil, and maintenance practices."

The specific objectives developed by the advisory committee are:

The LTPP program included two types of studies: General Pavement Studies (GPS) and Specific Pavement Studies (SPS). The GPS experiments include nearly 800 inservice pavement test sections that encompass a large array of site selection factors throughout the United States and Canada. The SPS generally were aimed at more intensive studies of a few independent variables for each of a number of study topics.

The great majority of test sections for the GPS have been selected from existing highways, but most of the test sections used in the SPS have been specifically designed and constructed pavements with the characteristics needed for the studies being undertaken. The sections for a specific SPS project are built at a single location with multiple projects constructed around the Nation and Canada. A single location is selected to maintain as much uniformity as possible in factors such as subgrade, traffic, and environment. The multiple projects provide data on the effects of variations in these subgrade, traffic, and environmental factors. It is expected that there will also be a number of custom designed and constructed sections to fill important cells for which existing highway sections are not available.

While considered separately for clarity of understanding and planning, the results from GPS and SPS will be very interactive, and some of the test sections will be shared between experiments.

1.3 Objective of the Guidelines for Data Collection

One of the primary difficulties in utilizing data collected before the LTPP program has been lack of uniformity. Another serious deficiency has been the omission of data that is significant to the performance of the pavements. The LTPP experiments have been designed carefully to ensure appropriate distributions of significant variables to support the objectives of these studies. Over a period of years a set of data collection guides has been developed that provides methodologies for the collection of all data required by the LTPP program—from construction to materials and traffic to distress—to support these experiment designs, as well as to provide a uniform basis for the collection of other detailed data that have not been identified as necessary for the LTPP studies. The philosophical approach taken has been not only to identify those data items that are considered to be of high priority for achieving the goals of the LTPP studies, but also to provide for a very comprehensive set of other data items that may be desirable in the LTPP Information Management System (IMS) for other purposes. These purposes include pavement management; very detailed studies of pavement components, construction techniques, design features; and other studies that may be conceived in the future.

The data collection guidelines were provided to the Regional Support Contractors (RSC) to facilitate data collection on a uniform basis. The original Data Collection Guide (DCG), referenced below, covered all types of LTPP data.
Data Collection Guide for Long-Term Pavement Performance Studies, Operational Guide No. SHRP-LTPP-OG-001, SHRP, National Research Council, Washington, DC, January 1988.

Over time, additional documents have been developed that provide more specific requirements and guidelines for the collection of LTPP data. The primary purpose of the various data collection guides is to provide a uniform basis for data collection during long-term monitoring of the performance of pavement test sections under study by the LTPP program that was initiated under SHRP and continued under FHWA.

The guides used in the LTPP studies are intended to provide sufficient detail for implementation of the LTPP studies; but it is recognized that future modifications and the addition of new documents will be necessary as the requirements for instrumentation and other LTPP research areas become more defined, and as automated distress and performance measures are applied. Emphasis has been given to ensuring the data items identified will be satisfactory over the long term so that critical data will not be missing from the LTPP IMS when it is used in the future to develop pavement performance models.

As methods data collection have changed and improved over the years, the guidelines used in obtaining these data have been modified. In some cases, actual changes were required to the guidelines to improve data collection; in other cases, the need was to clarify the guidelines. These changes and clarifications have been provided to the regions in the form of directives. This document provides references for the guidelines and subsequent revisions to those guidelines used in collecting each type of LTPP data over the lifetime of the LTPP program.

1.4 Categories of Data Collected

For data collection purposes, the data have been categorized as follows:

A chapter for each type of data collected is provided in the following pages. Within each chapter, references are provided detailing the methods used to collect the data in accordance with LTPP standards and specifying the timeframe during which those standards were relevant or the date at which current standards became relevant.

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