Quality and Accuracy of Positional Data in Transportation (2003)

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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. 2003 www.TRB.org NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM NCHRP REPORT 506 Research Sponsored by the American Association of State Highway and Transportation Officials in Cooperation with the Federal Highway Administration SUBJECT AREAS Planning and Administration • Highway and Facility Design Quality and Accuracy of Positional Data in Transportation E. S. FEKPE T. WINDHOLZ K. BEARD AND K. NOVAK Battelle Columbus, OH

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 506 Project SP20-47(01) FY 1998 ISSN 0077-5614 ISBN 0-309-08781-3 Library of Congress Control Number 20033115135 © 2003 Transportation Research Board Price $31.00 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 506 ROBERT J. REILLY, Director, Cooperative Research Programs CRAWFORD F. JENCKS, Manager, NCHRP CHRISTOPHER J. HEDGES, Senior Program Officer EILEEN P. DELANEY, Managing Editor HILARY FREER, Associate Editor II NCHRP PROJECT SP20-47 (1) PANEL Field of Special Projects—Area of Special Projects RON CIHON, Washington State DOT (Chair) DAVID W. BARANIAK, Lambda Tech International, Waukesha, WI JONATHAN J. DUCHATEAU, Wisconsin DOT CHRIS A. GLAZIER, Utah DOT MICHAEL F. GOODCHILD, University of California - Santa Barbara ELIZABETH A. HARPER, Parsons Brinckerhoff, Morrisville, NC BRAD JOHNSON, Fredericksburg, VA WENDE A. O’NEILL, Westat, Inc., Rockville, MD DARIS W. ORMESHER, South Dakota DOT MIKE NEATHERY, FHWA Liaison Representative THOMAS PALMERLEE, TRB Liaison Representative AUTHOR ACKNOWLEDGMENTS The research reported in this interim report was performed under the NCHRP Project 20-47(01) by Battelle, Columbus, Ohio, in association with the Department of Spatial Information Science and Engineering, National Center for Geographic Information and Analysis, University of Maine, Orono, Maine; TRANSMAP Cor- poration, Columbus, Ohio; and ND-Lea Engineers and Planners, Winnipeg, Canada. Dr. Edward Fekpe, Senior Research Scientist, Battelle, was the principal investigator. The other authors of this report are Dr. Kate Beard of the Department of Spatial Information Science and Engi- neering, National Center for Geographic Information and Analysis, University of Maine; Dr. Kurt Novak of TRANSMAP Corporation; and Dr. Thomas Windholz of Idaho State University (formerly of University of Maine). Other research team members who con- tributed to the development of this report are Mr. Mohammed Alam, Mr. Mohammed Majed, Mr. Deepak Gopalakrishna, and Ms. Melissa Murphy of Battelle; Mr. Tony Zifer and John Yablon- ski of TRANSMAP Corporation; and Ms. Kerra Mruss of ND-Lea.

This report presents guidance for practitioners on the use of positional, or spatial, data in Geographic Information Systems (GIS) for transportation applications. As GIS applications become more common in transportation-system management and decision making, concerns have grown about the accuracy of the data used to populate them. Transportation spatial data usually describes the location of features on the highway system using a one-dimensional linear referencing system. The level of accuracy varies by data source and is affected by the precision of the measurement system used to col- lect it. Agencies need a way to understand the errors that may result when using these data in GIS applications and how these errors may be compounded when combining data from various sources. This project reviewed the linear referencing systems used by state DOTs, examined the limitations of typical data sources used in these systems, and developed a model to evaluate the effects of varying data accuracy and provide an assessment of the level of confidence in the system outputs. This report will provide valuable information to transportation practitioners who need to understand and account for the level of precision in GIS-based transportation decision tools. Most transportation data are linearly referenced in a one-dimensional (1D) model. The implications of spatial data quality in the 1D model are not well understood, thereby significantly limiting the value of analyses using these data and the efficacy of subsequent decision making. Many methods have been used to measure the positions of objects or events rela- tive to the highway network, and technologies such as Global Positioning Systems (GPS) are providing highly efficient means for accurately establishing 2D and 3D positions that can be used to locate point features such as accidents, signs, and inter- sections rapidly and conveniently. GPS can also be used for locating moving vehicles in real time. Difficulties arise with the use of GPS technology because, traditionally, the location component of a data item is captured in coordinates (2D) that must be transformed to some linear reference such as log-mile point (1D). Moreover, analyti- cal operations on spatial data, in support of transportation applications, are compli- cated because coordinate geometry cannot be applied to positions referenced in linear space (e.g., the distance from A to B is measured along a path, not along a straight line between coordinates). Designers and managers of GIS need guidance on the appropriate scales and num- ber of calibration points in formulating DOT base maps. Practitioners using GIS- generated data summaries need to know the bounds on “true” location that can be derived from the integration of diverse data sources (e.g., data collected using distance measuring instruments and GPS). There is also a need for methods that will allow the transformation between location referencing systems in the field and in the office and measures of the confidence limits of these transformations. FOREWORD By Christopher J. Hedges Staff Officer Transportation Research Board

Under NCHRP Project 20-47(01), a research team led by Edward Fekpe of Bat- telle began by describing the characteristics of spatial data, including linear referenc- ing methods and systems. The research team then evaluated the quality and precision of available spatial data sources, given the accuracy capabilities of current spatial data measurement methods. After reviewing transportation applications for spatial data and their sensitivity to data quality, the research team developed a prototype error model that can be used to understand the effects of using and combining typical data sources. The outputs of the model list the confidence values at various probabilities associated with specific data sources for a wide range of transportation applications. The error model is implemented as a software program called GISError. It was developed in Visual Basic with a graphical user interface, and is included with this report on CRP- CD-41. A user guide for GISError is included in the report as Appendix A.

1 SUMMARY 4 CHAPTER 1 Introduction and Research Approach 1.1 Problem Statement, 4 1.2 Objectives and Scope, 4 1.3 Report Organization, 4 6 CHAPTER 2 Findings 2.1 Spatial Data Characteristics, 6 2.2 Spatial Data Quality, 11 2.3 Applications of Positional Data, 17 2.4 Measurement Systems, 22 2.5 Modeling Data Error, 28 45 CHAPTER 3 Interpretation, Appraisal, and Applications 3.1 Discussion of Case Studies, 45 3.2 Indices of Positional Data Quality, 53 3.3 Recommendations for Positional Data Quality Standards, 55 61 CHAPTER 4 Conclusions and Suggested Research 4.1 Conclusions, 61 4.2 Suggested Research, 62 63 REFERENCES 67 ABBREVIATIONS AND ACRONYMS A-1 APPENDIX A Prototype Data Error Model (GisError) User Guide B-1 APPENDIX B Results of Case Studies C-1 APPENDIX C Questionnaire for State DOT Interviews CONTENTS