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Publication Number:  FHWA-HRT-07-040    Date:  October 2011
Publication Number: FHWA-HRT-07-040
Date: October 2011


Falling Weight Deflectometer Calibration Center and Operational Improvements: Redevelopment of The Calibration Protocol and Equipment

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This report details the critical updates to the Strategic Highway Research Program falling weight deflectometer (FWD) calibration procedure. This has led to the revision of the American Association of State Highway and Transportation Officials R32-09 calibration procedure.(1) The report describes the procedural improvements and provides information on how to calibrate an FWD according to the updated procedure. Appendices provide the updated protocol for FWD calibration, drawings and specifications of the hardware needed, an updated specification for the pavement deflection data exchange (PDDX) protocol, and a flowchart for the new calibration software, WinFWDCal. This report will be of interest to engineers who perform structural evaluation of pavements. This final report covers the initial 2-year phase I and the subsequent task orders 1 and 2 of the pooled fund study TPF-5(039).

Jorge E. Pagán-Ortiz
Director, Office of Infrastructure
Research and Development


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.

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 Report Documentation Page

1. Report No.


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

Falling Weight Deflectometer Calibration Center and Operational Improvements: Redevelopment of the Calibration Protocol and Equipment

5. Report Date

October 2011

6. Performing Organization Code
7. Author(s)

Lynne H. Irwin, David P. Orr, and Daniel Atkins

8. Performing Organization Report No.

CLRP Report No. 2010-03

9. Performing Organization Name and Address

Cornell University Local Roads Program
416 Riley-Robb Hall
Ithaca, NY 14853

10. Work Unit No. (TRAIS)

11. Contract or Grant No.


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, September 2004–October 2010

14. Sponsoring Agency Code


15. Supplementary Notes

The Contracting Officer’s Technical Representatives (COTR) are Eric Weaver (2004–2008) and Jane Jiang (2008–2011).

16. Abstract

The objective of this project is to upgrade the existing falling weight deflectometer (FWD) calibration system to make calibration sustainable for the next decade without a loss of quality while ensuring that any new procedures are compatible with all brands of FWDs sold in the United States. This involves upgrading the hardware and software used in calibration to take advantage of improvements in technology. The primary result of the FWD calibration procedure is to obtain gain factors used to correct FWD load and deflection sensor data to agree with the calibration instrumentation.

Changes incorporated in the new FWD calibration procedure include replacing the reference linear variable differential transducer with an accelerometer for deflection sensor calibration, developing a stiff multiple-sensor stand to allow calibration of all deflection sensors simultaneously, updating the calibration software to a modern programming language with the ability to electronically read data from each brand of FWD, and using modern data acquisition techniques to eliminate sensitivity problems from the older Strategic Highway Research Program FWD calibration protocol. The time to complete an FWD calibration was greatly reduced. This report outlines the updated procedures and provides details about the equipment and methods needed to perform the updated protocol.

17. Key Words

Deflection measurement, Falling weight deflectometer, FWD, Backcalculation, Calibration, PDDX

18. Distribution Statement

No restrictions. This document is available through the National Technical Information Service, Springfield, VA 22161.

19. Security Classification
(of this report)


20. Security Classification
(of this page)


21. No. of Pages


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

SI* (Modern Metric) Conversion Factors

*SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380.
(Revised March 2003)






AASHTO American Association of State Highway and Transportation Officials
AMRL AASHTO Materials Reference Laboratory
ANOVA Analysis of variance
ASCII American Standard Code for Information Interchange
ASTM American Society for Testing and Materials
Caltrans  California Department of Transportation
CDOT Colorado Department of Transportation
CLRP Cornell Local Roads Program
DAQ Data acquisition board
EMI Electromagnetic interference
FHWA Federal Highway Administration
FWD Falling weight deflectometer
HWD Heavy weight deflectometer
INDOT Indiana Department of Transportation
ISA Industry standard(s) architecture
LTPP Long-term pavement performance
LVDT Linear variable differential transducer
MDT Montana Department of Transportation
MEMS Microelectromechanical systems
micron (μm) One millionth of a meter or 0.0039 mil
mil One thousandth of an inch or 25.4 microns
Mn/DOT Minnesota Department of Transportation
NIST National Institute of Standards and Technology
PCI Peripheral component interconnect
PDDX Pavement deflection data exchange
PennDOT Pennsylvania Department of Transportation
QC/QA Quality control/quality assurance
SHRP Strategic Highway Research Program
TxDOT Texas Department of Transportation
USB Universal serial bus


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