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Publication Number:  FHWA-HRT-13-090    Date:  April 2016
Publication Number: FHWA-HRT-13-090
Date: April 2016

 

MEPDG Traffic Loading Defaults Derived From Traffic Pooled Fund Study

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FOREWORD

The Mechanistic-Empirical Pavement Design Guide (MEPDG), Interim Edition: A Manual of Practice requires detailed axle loading information in the form of normalized axle load spectra (NALS), number of axles per truck class and axle group types, and axle spacing inputs as part of traffic loading inputs.(1) These data are obtained from weigh-in-motion (WIM) sites.

The objectives of this project were to evaluate the applicability of the existing MEPDG global traffic loading defaults and to use research-quality WIM data from the Long-Term Pavement Performance (LTPP) Specific Pavement Study (SPS) Traffic Data Collection pooled fund study to revise and improve the global default axle loading values.(2) This report provides an assessment of the original MEPDG axle loading defaults, describes WIM data selection criteria, including data reliability assessment, presents findings from the LTPP SPS traffic pooled fund study traffic data review, describes a methodology to generate new MEPDG traffic loading defaults, and provides a description of the new traffic loading defaults and recommendations for their use.

The report also discusses a sensitivity analysis of MEPDG pavement performance models to NALS. Significant differences found in the MEPDG outcomes support the need for axle loading characterization beyond a simple default value for heavy trucks that dominate vehicle class distributions, especially for class 9 trucks. The effect of WIM accuracy on axle weight measurements, NALS estimates, and the associated MEPDG outcomes was also investigated.

Mark Swanlund
Acting Director, Office of Infrastructure

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.

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The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Technical Report Documentation Page

1. Report No.

FHWA-HRT-13-090

2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

MEPDG Traffic Loading Defaults Derived from Traffic Pooled Fund Study

5. Report Date

April 2016

6. Performing Organization Code
7. Author(s)

O.I. Selezneva, M. Ayres, M. Hallenbeck, A. Ramachandran, H. Shirazi, and H. Von Quintus

8. Performing Organization Report No.

9. Performing Organization Name and Address

Applied Research Associates, Inc.
7184 Troy Hill Drive, Suite N
Elkridge, MD 21075-7056

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-02-C-00138

12. Sponsoring Agency Name and Address

Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

13. Type of Report and Period Covered

Final Report

14. Sponsoring Agency Code

15. Supplementary Notes

The Contracting Officer's Representative (COR) was Larry Wiser, HRDI-30, Long-Term Pavement Performance Data Analysis Contract.

16. Abstract

As part of traffic loading inputs, the Mechanistic-Empirical Pavement Design Guide (MEPDG), Interim Edition: A Manual of Practice requires detailed axle loading information in the form of normalized axle load spectra (NALS), number of axle per truck class and axle group types, and axle spacing inputs.(1) These data are obtained from weigh-in-motion (WIM) sites.

The objective of this project was to evaluate the applicability of the existing MEPDG global traffic loading defaults and to use research-quality WIM data from the Long-Term Pavement Performance (LTPP) Specific Pavement Studies (SPS) Traffic Data Collection pooled fund study to revise and improve the global default axle loading values.(2) This report provides an assessment of the original MEPDG axle loading defaults, describes WIM data selection criteria, including data reliability assessment, presents findings from the LTPP SPS traffic pooled fund study traffic data review, describes a methodology to generate new MEPDG traffic loading defaults, and provides a description of the new traffic loading defaults and recommendations for their use.

The report also discusses a sensitivity analysis of MEPDG pavement performance models to NALS. Significant differences found in the MEPDG outcomes support the need for axle loading characterization beyond a simple default value for heavy trucks that dominate vehicle class distributions, especially for class 9 trucks. The effect of WIM accuracy on axle weight measurements, NALS estimates, and the associated MEPDG outcomes was also investigated. It was found that drift in WIM system calibration leading to over 5 percent bias in mean error between true and WIM-measured axle weight could lead to significant differences in MEPDG design outcomes. In addition, two new statistical parameters were developed in this study: (1) a summary statistic used to describe traffic loads for comparison and grouping of similar NALS called the relative pavement performance impact factor and (2) a parameter used to quantify errors associated with NALS and to assess NALS reliability called the pooled weighted load error.

17. Key Words

Long-term performance, Traffic pooled fund study, Mechanistic-Empirical Pavement Design Guide, Weigh-in-motion, Load spectra

18. Distribution Statement

No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161.
http://www.ntis.gov

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

206

22. Price
Form DOT F 1700.7 (8-72)   Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

Table of Contents

CHAPTER 1-INTRODUCTION

CHAPTER 2-REVIEW OF MEPDG TRAFFIC LOADING DEFAULTS

CHAPTER 3-SUMMARY OF IMPROVEMENTS IN LTPP TRAFFIC DATA SINCE ORIGINAL MEPDG DEFAULTS

CHAPTER 4-IMPORTANCE OF AXLE LOADS FOR PAVEMENT DESIGN USING THE MEPDG

CHAPTER 5-METHODOLOGY FOR ESTIMATING RELIABILITY OF TRAFFIC LOADING DATA

CHAPTER 6-ANALYSIS OF AXLE LOAD SPECTRA VARIABILITY USING SPS TPF WIM DATA

CHAPTER 7-DATA SELECTION CRITERIA FOR DEVELOPMENT OF MEPDG AXLE LOADING DEFAULTS AND RESULTS OF DATA ASSESSMENT

CHAPTER 8-METHODOLOGY FOR DEVELOPMENT OF MEPDG TRAFFIC LOADING DEFAULTS USING LTPP SPS TPF DATA

CHAPTER 9-MEPDG SENSITIVITY TO DIFFERENT AXLE LOAD SPECTRA CLUSTERS

CHAPTER 10-DESCRIPTION OF THE NEW MEPDG TRAFFIC LOADING DEFAULTS FOR LTPP SITES

CHAPTER 11-SUMMARY OF FINDINGS AND RECOMMENDATIONS

APPENDIX A-RESULTS OF MONTHLY AXLE LOAD TEMPORAL CONSISTENCY AND OUTLIER ANALYSIS

APPENDIX B-EVALUATION OF ATYPICAL APC COEFFICIENTS

APPENDIX C-STATISTICAL CLUSTER ASSIGNMENTS FOR LTPP SPS TPF SITES used FOR MEPDG SENSITIVITY ANALYSIS

APPENDIX D-DATABASE CD AND DATA DICTIONARY

REFERENCES

List of Figures

List of Tables

List of Abbreviations

AADTT average annual daily truck traffic  
AASHTO American Association of State Highway and Transportation Officials  
AC asphalt concrete  
APC axle per class  
AVC automatic vehicle classification  
CF confidence factor  
CL confidence level  
DOW day of the week  
ESAL equivalent single-axle load  
ETG expert task group  
FHWA Federal Highway Administration  
GP load cluster group  
GPS General Pavement Studies  
GVW gross vehicle weight  
HMA hot mix asphalt  
IRI International Roughness Index  
JPCP jointed plain concrete pavement  
LTAS Long-Term Pavement Performance Traffic Analysis Software  
LTPP Long-Term Pavement Performance  
MEPDG Mechanistic-Empirical Pavement Design Guide  
M.P. Milepost  
NALS normalized axle load spectra  
NCHRP National Cooperative Highway Research Program  
PCC portland cement concrete  
PLUG Pavement Loading User Guide  
PWLE pooled weighted load error  
PVR per vehicle record  
QA quality assurance  
QC quality control  
RANALS representative annual normalized axle load spectra  
RI rural interstate  
ROPA rural other principal arterial  
RPPIF relative pavement performance impact factor  
SDR Standard Data Release  
SHRP Strategic Highway Research Program  
SPS Specific Pavement Studies  
TPF transportation pooled fund  
TTC truck traffic classification  
VCD vehicle class distribution  
WIM weigh-in-motion

 

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