National Academies Press: OpenBook

Validation of Urban Freeway Models (2014)

Chapter: Front Matter

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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2014. Validation of Urban Freeway Models. Washington, DC: The National Academies Press. doi: 10.17226/22282.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

TRANSPORTATION RESEARCH BOARD WASHINGTON, D.C. 2015 www.TRB.org The Second S T R A T E G I C H I G H W A Y R E S E A R C H P R O G R A M REPORT S2-L33-RW-1 Validation of Urban Freeway Models RobeRt HRanac, tiffany baRkley, kavya Sambana, and bRian deRStine Iteris, Inc. Berkeley, California Pitu miRcHandani and ZHuoyang ZHou Arizona State University Phoenix, Arizona Soyoung aHn University of Wisconsin–Madison

Subject Areas Highways Operations and Traffic Management Planning and Forecasting

The Second Strategic Highway Research Program America’s highway system is critical to meeting the mobility and economic needs of local communities, regions, and the nation. Developments in research and technology—such as advanced materials, communications technology, new data collection tech- nologies, and human factors science—offer a new opportunity to improve the safety and reliability of this important national resource. Breakthrough resolution of significant transportation problems, however, requires concentrated resources over a short time frame. Reflecting this need, the second Strategic Highway Research Program (SHRP 2) has an intense, large-scale focus, integrates multiple fields of research and technology, and is fundamentally different from the broad, mission-oriented, discipline-based research programs that have been the mainstay of the highway research industry for half a century. The need for SHRP 2 was identified in TRB Special Report 260: Strategic Highway Research: Saving Lives, Reducing Congestion, Improving Quality of Life, published in 2001 and based on a study sponsored by Congress through the Transportation Equity Act for the 21st Century (TEA-21). SHRP 2, modeled after the first Strategic Highway Research Program, is a focused, time- constrained, management-driven program designed to com- plement existing highway research programs. SHRP 2 focuses on applied research in four areas: Safety, to prevent or reduce the severity of highway crashes by understanding driver behavior; Renewal, to address the aging infrastructure through rapid design and construction methods that cause minimal disruptions and produce lasting facilities; Reliability, to reduce congestion through incident reduction, management, response, and mitigation; and Capacity, to integrate mobility, economic, environmental, and community needs in the planning and designing of new trans- portation capacity. SHRP 2 was authorized in August 2005 as part of the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU). The program is managed by the Transportation Research Board (TRB) on behalf of the National Research Council (NRC). SHRP 2 is conducted under a memo- randum of understanding among the American Association of State Highway and Transportation Officials (AASHTO), the Federal Highway Administration (FHWA), and the National Academy of Sciences, parent organization of TRB and NRC. The program provides for competitive, merit-based selection of research contractors; independent research project oversight; and dissemination of research results. SHRP 2 Reports Available by subscription and through the TRB online bookstore: www.mytrb.org/store Contact the TRB Business Office: 202-334-3213 More information about SHRP 2: www.TRB.org/SHRP2 SHRP 2 Report S2-L33-RW-1 ISBN: 978-0-309-27424-1 © 2015 National Academy of Sciences. All rights reserved. Copyright Information Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copy- right to any previously published or copyrighted material used herein. The second Strategic Highway Research Program grants permission to repro- duce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, or FHWA endorsement of a particular prod- uct, method, or practice. It is expected that those reproducing material in this document for educational and not-for-profit purposes will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from SHRP 2. Note: SHRP 2 report numbers convey the program, focus area, project number, and publication format. Report numbers ending in “w” are published as web documents only. Notice The project that is the subject of this report was a part of the second Strategic Highway Research Program, conducted by the Transportation Research Board with the approval of the Governing Board of the National Research Council. The members of the technical committee selected to monitor this project and review this report were chosen for their special competencies and with regard for appropriate balance. The report was reviewed by the technical committee and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the Governing Board of the National Research Council. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board, the National Research Council, or the program sponsors. The Transportation Research Board of the National Academies, the National Research Council, and the sponsors of the second Strategic 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 the report.

The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars 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 Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy 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. C. D. (Dan) Mote, Jr., 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. Victor J. Dzau 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 Academy, 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 Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. C. D. (Dan) Mote, Jr., are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is one of six major divisions of the National Research Council. The mission of the Transportation Research Board is to provide leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisci- plinary, and multimodal. The Board’s varied activities annually engage about 7,000 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 Transporta- tion, and other organizations and individuals interested in the development of transportation. www.TRB.org www.national-academies.org

ACKNOWLEDGMENTS This work was sponsored by the Federal Highway Administration in cooperation with the American Asso- ciation of State Highway and Transportation Officials. It was conducted in the second Strategic Highway Research Program (SHRP 2), which is administered by the Transportation Research Board of the National Academies. The project was managed by William Hyman, Senior Program Officer for SHRP 2 Reliability. The research reported was performed by Iteris, Inc., supported by Arizona State University and the University of Wisconsin. Robert Hranac of Iteris, Inc., was the principal investigator. The other authors of this report are Tiffany Barkley, Kavya Sambana, and Brian Derstine of Iteris, Inc.; Pitu Mirchandani and Zhuoyang Zhou of Arizona State University; and Soyoung Ahn of the University of Wisconsin–Madison. Iteris, Inc., received technical assistance about the source data from the following agencies: Minnesota Department of Transportation (MnDOT), Utah Department of Transportation (UDOT), Washington State Department of Transportation, and the California Department of Transportation (CalTrans). SHRP 2 STAFF Ann M. Brach, Director Stephen J. Andrle, Deputy Director Cynthia Allen, Editor Kenneth Campbell, Chief Program Officer, Safety Jared Cazel, Editorial Assistant JoAnn Coleman, Senior Program Assistant, Capacity and Reliability Eduardo Cusicanqui, Financial Officer Richard Deering, Special Consultant, Safety Data Phase 1 Planning Shantia Douglas, Senior Financial Assistant Charles Fay, Senior Program Officer, Safety Carol Ford, Senior Program Assistant, Renewal and Safety James Hedlund, Special Consultant, Safety Coordination Alyssa Hernandez, Reports Coordinator Ralph Hessian, Special Consultant, Capacity and Reliability Andy Horosko, Special Consultant, Safety Field Data Collection William Hyman, Senior Program Officer, Reliability Linda Mason, Communications Officer David Plazak, Senior Program Officer, Capacity and Reliability Rachel Taylor, Senior Editorial Assistant Dean Trackman, Managing Editor Connie Woldu, Administrative Coordinator

This report describes the methodology, data, conclusions, and enhanced models regarding the validation of two sets of models developed in SHRP 2 Reliability Project L03, Analytical Procedures for Determining the Impacts of Reliability Mitigation Strategies. The signifi- cance of the L03 models is they were among the first models that could be used to predict travel time reliability. Loosely speaking, reliability is defined as how travel time changes over time. More rig- orously, reliability is defined as “the level of consistency in travel conditions over time . . . measured by describing the distribution of travel times that occur over a substantial period of time.”1 Specific reliability measures can be derived from the travel time distribution, such as the standard deviation and the Travel Time Index (n), or TTIn, which is the nth percentile of the travel time distribution divided by the free-flow travel time. Two sets of models were developed in Project L03, the data-poor and the data-rich models. The data-poor models predict a measure of reliability as a function of just the mean Travel Time Index, except for the on-time measures. Because these data-poor models have but one independent variable, these simple models provide a great deal of versatility in estimating reliability. Data-poor models enable the use of straightforward equations for predicting reli- ability in sketch planning and in complex modeling systems such as a trip-based demand model married to a network model. The data-rich models predict a measure of the variability of travel time as a function of a number of important variables that Project L03 found to be meaningful explanatory vari- ables: the demand-to-capacity ratio, lane-hours lost (due to traffic incidents or work zones), and rainfall. The data-rich models can be used to predict or estimate reliability when any of these causal variables appear in an equation and data are available. Both the data-poor and data-rich models were estimated from data collected over a year from a subset of urban freeway segments in seven cities. The data-poor models apply to all time slices throughout a day, whereas four sets of data-rich models concerning different moments of the TTI distribution (mean, 99th, 95th, 90th, 80th, 50th, and 10th percentiles) were estimated for the peak hour, the peak period, the midday, and weekdays. The objectives of Project L33, Validation of Urban Freeway Models, were threefold: (1) attempt to validate the “data-poor” and “data-rich” models, (2) develop enhanced models if justified, and (3) promote acceptance and use of the L03 type of models for planning, programming, project development, design, systems operations, and further research. F O R E W O R D William Hyman, SHRP 2 Senior Program Officer, Reliability 1 Cambridge Systematics, Texas Transportation Institute, University of Washington, and Dowling Associates. 2006. NCHRP Web-Only Document 97: Guide to Effective Freeway Performance Measurement: Final Report and Guidebook. Transportation Research Board of the National Academies, Washington, D.C.

In conducting the validation, the research team was prohibited from using data that were used to estimate the data-poor and data-rich models. Validation data came from California, Minnesota, Utah (Salt Lake City), and Washington (Spokane) and totaled 323 segment-years covering both midday and peak periods. L03 models used data from some of these same places, but the same data were not used in the validation, as required. The project used two criteria for assessing the validity of the L03 models. The first was the difference between the predicted and measured values of the dependent variable. The second was whether the estimated models satisfied the assumptions of linear regression. This report describes the degree to which the different models perform well in terms of prediction and satisfying regression assumptions. The data-poor models predicted accept- ably well as documented here but had some shortcomings in terms of satisfying the regression assumptions. Three sets of enhanced models were developed. The research team could not find satisfactory enhancements to the data-rich models. The degree to which the data-rich models predict well and satisfy the assumptions of linear regression is also described in the report.

C O N T E N T S 1 Executive Summary 4 CHAPTER 1 Background 4 Context 4 L03 Review 7 Research Questions 7 Final Report Structure 9 Reference 10 CHAPTER 2 Data 10 Sites 10 Processing 11 Characteristics 14 Summary 18 CHAPTER 3 Existing Model Validation 18 Overview 19 Data-Rich Validation 21 Data-Poor Validation 22 Reference 23 CHAPTER 4 Enhanced Models and Application Guidelines 23 Overview 23 Results 25 Application Guidelines 26 Appendix A. Review of L03 and Related Models 48 Appendix B. Validation Plan 65 Appendix C. Data-Rich Validation 167 Appendix D. Data-Poor Validation 217 Appendix E. Model Enhancements

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TRB’s second Strategic Highway Research Program (SHRP 2) Report S2-L33-RW-1: Validation of Urban Freeway Models documents and presents the results of a project to investigate, validate, and enhance the travel time reliability models developed in the SHRP 2 L03 project titled Analytical Procedures for Determining the Impacts of Reliability Mitigation Strategies.

This report explores the use of new datasets and statistical performance measures to validate these models. As part of this validation, this work examined the structure, inputs, and outputs of all of the L33 project models and explored the applicability and validity of all L03 project models. This report proposes new application guidelines and enhancements to the L03 models.

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