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Publication Number: FHWA-HRT-08-065
Date: November 2008

Long-Term Pavement Performance Compliance With Department of Transportation Information Dissemination Quality Guidelines

CHAPTER 3. LTPP DATA PROCESSING

LTPP's data processing operations started in 1988 at a time when modern database software was evolving. In the development of the data quality approach to LTPP data, all of the features covered in the IDQG were addressed. The data QC process started with procedures to calibrate and check the functioning of field data collection equipment. Data forms and data collection procedures always received an independent review prior to use. Extensive data editing checks were developed to automate the process of identifying and correcting erroneous data. Methods were developed to identify and address missing data. A codified procedure was developed to address the issue of computed parameters containing estimates, projects, and imputations. The data analysis plan and analyses were subjected to scrutiny from an expert panel operating outside the program.

Data Editing and Coding

Efforts are made to reduce errors at the source, i.e., during data collection. An extensive number of methods have been developed to identify, and where possible, correct erroneous data. Data checks are made before and after data are entered into the database. A primary objective of the data checks made prior to entry is to prevent "bad" data from being entered into the database. Some of the data editing and coding methods used by the LTPP program include the following:

Handling Missing Data, Estimates, and Projections

The approach to handling missing data, production of estimates, and projections for the LTPP program is similar enough to be classified under one topic.

Production of Estimates and Projections

Due to the research nature of the LTPP program, there is a division between the LTPP database and the LTPP data analysis results. The responses to LTPP's actions relative to this part of the IDQG will focus on database contents. Discussion of production of estimates and projections from LTPP-sponsored analysis of the data are presented in the next portion of this document.

The LTPP database contains a vast array of derived data to enhance the data set and reduce user and data supplier burden. Since a primary purpose of the database is to provide raw data to researchers and analysts, only a limited number of estimates are contained in the database. Virtually no projections are contained in the database. These quantities are contained in published analysis reports distributed independently of the database.

Examples of derived data contained in the database include the following:

Data Analysis and Interpretation

A multiproject approach by topic area is used for analysis of LTPP data. To date, there have been approximately 55 analysis projects performed under LTPP management and 21 LTPP analysis projects performed under the auspices and funding of the NCHRP. There have been more NCHRP- and State-sponsored research projects that have used LTPP data. With this volume of research, it is easy to understand that no single approach is used for LTPP data analysis, and different approaches have been used for analysis of the same set of data.

The bulk of LTPP sponsored analyses are performed under contracts with consultants, experts, academicians, and university researchers. Thus, a formal contractual approach to analysis is used. Topics are selected from the LTPP analysis plan; formal statements of work are developed; request for proposals are issued; proposals are evaluated; a contactor is selected; on some projects a project panel is used to review work in progress; and all results are reviewed prior to publication.

Highlights of LTPP conformance to the IDQG relative to data analysis and interpretation are as follows:

 

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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).
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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