Skip to contentUnited States Department of Transportation - Federal Highway Administration FHWA Home
Research Home   |   Pavements Home
Report
This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-RD-03-040
Date: July 2002

Researcher's Guide to The LTPP Layer Thickness Data

Previous | Table of Contents | Next

  1. Recommend Layer Thickness Data Sources for Section-Level Analyses
  2. Recommend Layer Thickness Data Sources for Locations-Specific Analyses
  3. Recommend Layer Thickness Variability Data Sources

Pavement layer thickness data are an essential input to pavement engineering analyses. The accuracy of layer thickness data has a great impact on the outcome of practically all analyses of performance. Based on the analysis type, thickness data at the "section level" or "location-specific" thickness measurements may be required. Additionally, variability information may be required for reliability-based pavement analyses. Examples of section-level analyses could be pavement performance modeling or mechanistic pavement structural analysis. For these types of analyses, the representative layer thicknesses are recommended. These thicknesses provide an overall estimate of characteristic layer thickness for the section that is being analyzed.

Example of location-specific analysis includes back calculation of pavement layer moduli. This analysis is based on interpretation of the deflection data obtained at the specific locations along the section. Layer thickness data from the specific locations where FWD tests were conducted could help to achieve more accurate results. An example of the analyses where thickness variability information is needed is reliability-based pavement performance modeling and design.

This chapter provides guidelines for searching the LTPP database for the most appropriate layer thickness data for different research purposes.

Recommended Layer Thickness Data Sources for Section-Level Analyses

Recommended layer thickness data sources for section-level analyses are summarized by the experiment type.

GPS sections:

Priority 1 The TST_L05B table is the most complete and accurate source for the representative layer thickness data.
Priority 2 If thickness data in this table are not available, data from TST_L05A could be used to determine representative thickness. TST_L05A contains laboratory- measured layer thickness data from up to three locations (beginning, within, and end of the section). Representative thickness is determined by averaging thickness values from different locations.
Priority 3 If thickness data are not available in either the TST_L05B or the TST_L05A table, representative layer thickness data from INV_LAYER (for construction event number 1) or RHB_LAYER (for construction event number 2 or above) could be used. Layer thickness data from these tables are the best estimate provided by the local highway agencies based on the existing documentation that was created prior to the LTPP experiment.

SPS sections:

Priority 1 The recommended layer thickness data source for section level analyses is the TST_L05B table. This is the most complete and accurate source for the representative layer thickness.
Priority 2 If thickness data in this table are not available, data from TST_L05A could be used to determine representative thickness. TST_L05A could include layer thickness data measured at up to three locations (beginning, middle, and end of the section).
Priority 3 Another reliable source of representative layer thickness information is the SPS* _LAYER tables. These tables contain average layer thickness measurements obtained from the elevation shots taken after construction of each layer at over 50 locations along the section.

Recommended Layer Thickness Data Sources for Location-Specific Analyses

Recommended layer thickness data sources for location-specific analyses are summarized by the experiment type.

GPS sections:

Priority 1 If the layer material type is AC or PCC, recommended layer thickness data sources for location-specific analyses are the TST_AC01_LAYER and TST_PC06 tables. Layer thicknesses obtained from these tables are based on measurements of pavement cores obtained at different locations along the section. Alternatively, the TST_L05A table could be used.
Priority 2 If the layer material type is not AC or PCC, layer thickness data from the TST_L05A table provide layer thicknesses measured at up to three locations (beginning, middle, and end of the section).

SPS sections:

Priority 1 The recommended layer thickness data sources for location-specific analyses are the SPS* _LAYER_THICKNESS tables. These tables contain layer thickness measurements obtained from the elevation shots taken after construction of each layer at over 50 locations along the section.
Priority 2 If no thickness data are available in the SPS* _LAYER_THICKNESS tables and the layer material type is AC or PCC, the recommended layer thickness data sources for location-specific analyses are the TST_AC01_LAYER and TST_PC06 tables. Layer thicknesses obtained from these tables are based
Priority 3 If no thickness data are available in the SPS* _LAYER_THICKNESS tables and the layer material type is not AC or PCC, layer thickness data from the TST_L05A table provide layer thicknesses measured at up to three locations (beginning, middle, and end of the section).

Recommended Layer Thickness Variability Data Sources

Upon review of the available layer thickness variability data, the following recommendations for the LTPP sources of the layer thickness variability information were established:

Previous | Table of Contents | Next


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.
FHWA
United States Department of Transportation - Federal Highway Administration