Evaluation of LTPP Climatic Data for Use in Mechanistic-Empirical Pavement Design Guide Calibration and Other Pavement Analysis PUBLICATION NO. FHWA-HRT-15-019 MAY 2015 Research, Development, and Technology Turner-Fairbank Highway Research Center 6300 Georgetown Pike McLean, VA 22101-2296 FOREWORD This document presents the results of an evaluation of climate data from Modern-Era Retrospective Analysis for Research and Applications (MERRA) for use in the Long Term Pavement Performance (LTPP) Program and for other infrastructure applications. MERRA data were compared against the best available ground-based observations both statistically and in terms of effects on pavement performance as predicted using the Mechanistic-Empirical Pavement Design Guide (MEPDG). These analyses included a systematic quantitative evaluation of the sensitivity of MEPDG performance predictions to variations in fundamental climate parameters. A more extensive analysis of MERRA data included additional statistical analysis comparing operating weather station (OWS) and MERRA data, evaluation of the correctness of MEPDG surface shortwave radiation (SSR) calculations and comparison of MEPDG pavement performance predictions using OWS and MERRA climate data for more sections. The principal conclusion from these evaluations was that the MERRA climate data were as good as and in many cases substantially better than equivalent ground-based OWSs. MERRA is strongly recommended as the new future source for climate data in LTPP. Recommendations are provided for incorporating hourly MERRA data into the LTPP database. The LTPP program is an ongoing and active program. To obtain current information and access to other technical references, LTPP data users should visit the LTPP Web site at http://www.tfhrc.gov/pavement/ltpp/ltpp.htm. LTPP data requests, technical questions, and data user feedback can be submitted to LTPP customer service via e-mail at [email protected]. Jorge E. Pagán-Ortiz Director, Office of Infrastructure Research and Development 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. Quality Assurance Statement 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 DOCUMENTATION PAGE 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. FHWA-HRT-15-019 4. Title and Subtitle 5. Report Date Evaluation of Long-Term Pavement Performance (LTTP) Climatic Data for May 2015 Use in Mechanistic-Empirical Pavement Design Guide(MEPDG) Calibration 6. Performing Organization Code and Other Pavement Analysis 7. Author(s) 8. Performing Organization Report No. Charles W. Schwartz, Gary E. Elkins, Rui Li, Beth A. Visintine, Barton Forman, Gonzalo R. Rada, Jonathan L. Groeger 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) AMEC Environment and Infrastructure, Inc. 12000 Indian Creek Court, Suite F 11. Contract or Grant No. Beltsville, MD 20705-1242 DTFH61-11-C-00030 University of Maryland—College Park Department of Civil and Environmental Engineering 1173 Glenn L. Martin Hall College Park, MD 20742 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Office of Infrastructure Research and Development Final Report, May 2011–October 2014 Federal Highway Administration 6300 Georgetown Pike 14. Sponsoring Agency Code McLean, VA 22101-2296 15. Supplementary Notes The Contracting Officer’s Representative (COR) was Larry Wiser. 16. Abstract Improvements in the Long-Term Pavement Performance (LTPP) Program’s climate data are needed to support current and future research into climate effects on pavement materials, design, and performance. The calibration and enhancement of the Mechanistic-Empirical Pavement Design Guide (MEPDG) is just one example of these emerging needs. A newly emerging climate data source, the Modern-Era Retrospective Analysis for Research and Applications (MERRA), developed by the National Aeronautics and Space Administration (NASA) for its own in-house modeling needs, provides continuous hourly weather data starting in 1979 on a relatively fine-grained uniform grid. MERRA is based on a reanalysis model that combines computed model fields (e.g., atmospheric temperatures) with ground-, ocean-, atmospheric-, and satellite-based observations that are distributed irregularly in space and time. MERRA data are available at an hourly temporal resolution and 0.5 degrees latitude by 0.67 degrees longitude (approximately 31.1 by 37.30 mi at mid-latitudes) spatial resolution over the entire globe. MERRA data were compared against the best available ground-based observations both statistically and in terms of effects on pavement performance as predicted using the MEPDG. These analyses included a systematic quantitative evaluation of the sensitivity of MEPDG performance predictions to variations in fundamental climate parameters. More extensive analysis of MERRA data included additional statistical analysis comparing operating weather station (OWS) and MERRA data, evaluation of the correctness of MEPDG surface shortwave radiation (SSR) calculations and comparison of MEPDG pavement performance predictions using OWS and MERRA climate data for more sections. The principal conclusion from these evaluations was that the MERRA climate data were as good and in many cases substantially better than equivalent ground-based OWS data. Given these many benefits and very few if any significant limitations, MERRA is strongly recommended as the new future source for climate data in LTPP. Recommendations are provided for incorporating hourly MERRA data into the LTPP database. 17. Key Words 18. Distribution Statement Long-Term Pavement Performance, LTPP, climate data, pavement No restrictions. This document is available to design, pavement performance, solar radiation, virtual weather stations, the public through the National Technical Modern-Era Retrospective Analysis for Research and Applications, Information Service, Springfield, VA 22161. MERRA, Mechanistic Empirical Pavement Design Guide, MEPDG, http://www.ntis.gov hourly weather data 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 138 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized ii TABLE OF CONTENTS EXECUTIVE SUMMARY ...........................................................................................................1 CHAPTER 1. INTRODUCTION .................................................................................................9 STUDY BACKGROUND AND OBJECTIVES ....................................................................9 TERMINOLOGY ....................................................................................................................9 CHANGE IN PROJECT WORK PLAN .............................................................................10 MORE EXTENSIVE ANALYSIS OF MERRA DATA .....................................................10 REPORT ORGANIZATION ................................................................................................11 CHAPTER 2. LEGACY LTPP APPROACH TO CLIMATE DATA ....................................13 VIRTUAL WEATHER STATION CONCEPT ..................................................................13 DATA PROCESSING AND STORAGE .............................................................................15 ISSUES WITH LEGACY LTPP CLIMATE DATA APPROACH ..................................19 CHAPTER 3. CLIMATE DATA APPLICATIONS AND SOURCE CANDIDATES..........23 INFRASTRUCTURE APPLICATIONS .............................................................................23 Empirical Pavement Design ...............................................................................................23 Mechanistic-Empirical Pavement Design ..........................................................................23 Superpave Binder Specification .........................................................................................25 HIPERPAV® .....................................................................................................................25 Bridge Management ...........................................................................................................26 Summary of Existing Applications ....................................................................................26 CONVENTIONAL SOURCES OF CLIMATIC DATA ....................................................27 Automated Surface Observing System (ASOS) ................................................................29 Road Weather Information Systems (RWIS) ....................................................................29 Solar Radiation Data ..........................................................................................................29