Equipment for Collecting Traffic Load Data (2004)

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T R A N S P O R T A T I O N R E S E A R C H B O A R D WASHINGTON, D.C. 2004 www.TRB.org NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM NCHRP REPORT 509 Research Sponsored by the American Association of State Highway and Transportation Officials in Cooperation with the Federal Highway Administration SUBJECT AREAS Planning and Administration • Pavement Design, Management, and Performance • Bridges, Other Structures, and Hydraulics and Hydrology Equipment for Collecting Traffic Load Data MARK HALLENBECK Washington State Transportation Center University of Washington Seattle, WA AND HERBERT WEINBLATT Cambridge Systematics, Inc. Chevy Chase, MD

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Association and it receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board of the National Academies was requested by the Association to administer the research program because of the Board’s recognized objectivity and understanding of modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; it possesses avenues of communications and cooperation with federal, state and local governmental agencies, universities, and industry; its relationship to the National Research Council is an insurance of objectivity; it maintains a full-time research correlation staff of specialists in highway transportation matters to bring the findings of research directly to those who are in a position to use them. The program is developed on the basis of research needs identified by chief administrators of the highway and transportation departments and by committees of AASHTO. Each year, specific areas of research needs to be included in the program are proposed to the National Research Council and the Board by the American Association of State Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Research Council and the Transportation Research Board. The needs for highway research are many, and the National Cooperative Highway Research Program can make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or duplicate other highway research programs. Note: The Transportation Research Board of the National Academies, the National Research Council, the Federal Highway Administration, the American Association of State Highway and Transportation Officials, and the individual states participating in the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the object of this report. Published reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from: Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet at: http://www.national-academies.org/trb/bookstore Printed in the United States of America NCHRP REPORT 509 Project 1-39 FY’00 ISSN 0077-5614 ISBN 0-309-08788-0 Library of Congress Control Number 2004100961 © 2004 Transportation Research Board Price $20.00 NOTICE The project that is the subject of this report was a part of the National Cooperative Highway Research Program conducted by the Transportation Research Board with the approval of the Governing Board of the National Research Council. Such approval reflects the Governing Board’s judgment that the program concerned is of national importance and appropriate with respect to both the purposes and resources of the National Research Council. The members of the technical committee selected to monitor this project and to review this report were chosen for recognized scholarly competence and with due consideration for the balance of disciplines appropriate to the project. The opinions and conclusions expressed or implied are those of the research agency that performed the research, and, while they have been accepted as appropriate by the technical committee, they are not necessarily those of the Transportation Research Board, the National Research Council, the American Association of State Highway and Transportation Officials, or the Federal Highway Administration, U.S. Department of Transportation. Each report is reviewed and accepted for publication by the technical committee according to procedures established and monitored by the Transportation Research Board Executive Committee and the Governing Board of the National Research Council.

The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished schol- ars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. On the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and techni- cal matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Acad- emy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achieve- ments of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, on its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Acad- emy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both the Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is a division of the National Research Council, which serves the National Academy of Sciences and the National Academy of Engineering. The Board’s mission is to promote innovation and progress in transportation through research. In an objective and interdisciplinary setting, the Board facilitates the sharing of information on transportation practice and policy by researchers and practitioners; stimulates research and offers research management services that promote technical excellence; provides expert advice on transportation policy and programs; and disseminates research results broadly and encourages their implementation. The Board’s varied activities annually engage more than 4,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. www.TRB.org www.national-academies.org

COOPERATIVE RESEARCH PROGRAMS STAFF FOR NCHRP REPORT 509 ROBERT J. REILLY, Director, Cooperative Research Programs CRAWFORD F. JENCKS, Manager, National Cooperative Highway Research Program AMIR N. HANNA, Senior Program Officer EILEEN P. DELANEY, Managing Editor BETH HATCH, Assistant Editor ELLEN M. CHAFEE, Assistant Editor NCHRP PROJECT 1-39 PANEL Field of Design—Area of Pavements DANNY A. DAWOOD, Pennsylvania DOT (Chair) KENNETH W. FULTS, Texas DOT CHARLES K. CEROCKE, Nevada DOT HARSHAD DESAI, Florida DOT RALPH A. GILLMANN, FHWA JERRY LEGG, West Virginia DOT TED SCOTT, Roadway Express, Inc., Alexandria, VA ANDREW WILLIAMS, JR., Ohio DOT LARRY WISER, FHWA Liaison Representative STEPHEN F. MAHER, TRB Liaison Representative A. ROBERT RAAB, TRB Liaison Representative

This report identifies the key issues that must be considered by state and other high- way operating agencies in selecting traffic equipment for collecting the truck volumes and load spectra needed for analysis and design of pavement structures. The report also identifies steps that must be taken to ensure that the equipment performs appropriately and that, as a consequence, the data collected accurately describe the vehicles being monitored. The report is a useful resource for state personnel and others involved in the planning and design of highway pavements and structures. Traffic information is one of the key data elements required for the design and analysis of pavement structures. In the procedure used in the 1993 AASHTO Guide for Design of Pavement Structures, a mixed traffic stream of different axle loads and axle configurations is converted into a design traffic number by converting each expected axle load into an equivalent number of 18-kip, single-axle loads, known as equivalent single-axle loads (ESALs). Equivalency factors are used to determine the number of ESALs for each axle load and axle configuration. These factors are based on the pres- ent serviceability index (PSI) concept and depend on the pavement type and structure. Studies have shown that these factors also are influenced by pavement condition, dis- tress type, failure mode, and other parameters. A more direct and rational approach to the analysis and design of pavement struc- tures involves procedures that use mechanistic-empirical principles to estimate the effects of actual traffic on pavement response and distress. This approach has been used to develop a guide for the mechanistic-empirical design of new and rehabilitated pave- ment structures as part of NCHRP Project 1-37A. The mechanistic-based distress pre- diction models used in this guide will require specific data for each axle type and axle load group. Recognizing the constraints on resources available in state and local high- way agencies for traffic data collection, the guide will allow for various levels of traf- fic data collection and analysis. Because the anticipated guide will use traffic data inputs that differ from those cur- rently used in pavement design and analysis, there was an apparent need for research to provide clear information on traffic data and forecasting and to provide guidance on selection and operation of the equipment needed for collecting these data. This infor- mation will facilitate use of the anticipated guide. NCHRP Project 1-39 was conducted to address this need. Under NCHRP Project 1-39, “Traffic Data Collection, Analysis, and Forecasting for Mechanistic Pavement Design,” Cambridge Systematics, Inc., was assigned the objectives of (1) developing guidelines for collecting and forecasting traffic data to formulate load spectra for use in procedures proposed in the guide for mechanistic- empirical design and (2) providing guidance on selecting, installing, and operating traf- fic data collection equipment and handling traffic data. This report is concerned with FOREWORD By Amir N. Hanna Staff Officer Transportation Research Board

the latter objective; the first objective will be addressed in detail in the agency’s final report on the project. To accomplish the latter objective, the researchers identified the steps required to select the equipment necessary for collecting traffic load data. In these steps, the researchers identified the types of equipment available for collecting classification counts and for weighing vehicles in motion and provided detailed descriptions of var- ious technologies. As part of these descriptions, the researchers reviewed the strengths and weaknesses of each technology. Finally, the researchers provided guidance on selection of equipment by considering (1) data collection needs of users, (2) data han- dling requirements and capabilities, and (3) characteristics of available technologies. To facilitate implementation and use of equipment, the researchers also provided infor- mation on best practices for equipment use. The information contained in this report should be of interest to those involved in the planning and design of highway pavements and structures. It will be particularly useful to agencies contemplating collection of traffic data for use in conjunction with the guide for the mechanistic-empirical design of new and rehabilitated pavement structures.

1 SUMMARY 16 CHAPTER 1 Introduction 17 CHAPTER 2 Types of Equipment 2.1 Vehicle Classification, 17 2.2 WIM Data, 18 21 CHAPTER 3 Technology Descriptions 3.1 Vehicle Classification, 21 3.2 WIM, 33 41 CHAPTER 4 A Process for Selecting Equipment 4.1 Data Collection Needs, 41 4.2 Data Handling and Other Agency Considerations, 43 4.3 Understanding Equipment Characteristics, 43 46 CHAPTER 5 Best Practices for Equipment Use 5.1 Identify User Requirements, 46 5.2 Determine Site Location and System Requirements, 47 5.3 Determine Design Life and Accuracy Requirements, 48 5.4 Budget Necessary Resources, 49 5.5 Develop, Use, and Maintain a Quality Assurance Program, 50 5.6 Purchase Equipment with a Warranty, 52 5.7 Manage Equipment Installation, 53 5.8 Calibrate and Maintain Calibration of Equipment, 53 5.9 Conduct Preventive and Corrective Maintenance, 57 CONTENTS