Analytical Procedures for Determining the Impacts of Reliability Mitigation Strategies (2012)

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TRANSPORTATION RESEARCH BOARD WASHINGTON, D.C. 2013 www.TRB.org RepoRt S2-L03-RR-1 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 Analytical Procedures for Determining the Impacts of Reliability Mitigation Strategies Cambridge SyStematiCS, inC. with texaS a&m tranSportation inStitute univerSity of WaShington doWling aSSoCiateS Street SmartS herb levinSon heSham rakha

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SHRP 2 Reports Available by subscription and through the TRB online bookstore: www.TRB.org/bookstore Contact the TRB Business Office: 202-334-3213 More information about SHRP 2: www.TRB.org/SHRP2 SHRP 2 Report S2-L03-RR-1 ISBN: 978-0-309-12926-8 Library of Congress Control Number: 2012953551 © 2013 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. Per- mission is given with the understanding that none of the material will be used to imply TRB, AASHTO, or FHWA endorsement of a particular product, method, or practice. 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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 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 technologies, and human factors science—offer a new oppor- tunity to improve the safety and reliability of this important national resource. Breakthrough resolution of significant trans- portation 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, manage- ment-driven program designed to complement 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 inte- grate mobility, economic, environmental, and community needs in the planning and designing of new transportation 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.

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. Charles M. Vest 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 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. Charles M. Vest 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 Associa- tion of State Highway and Transportation Officials. It was conducted in the second Strategic Highway Research Program, which is administered by the Transportation Research Board of the National Academies. The project was managed by William Hyman, Senior Program Officer for Reliability. The research described in this report was performed by Cambridge Systematics, Inc., supported by the Texas Transportation Institute, Dowling Associates, the University of Washington, Street Smarts, Herb Levinson, and Hesham Rakha. Richard Margiotta, Cambridge Systematics, Inc., was the principal investi- gator, and Tim Lomax, Texas Transportation Institute, was the co-principal investigator. The other authors of this report are Mark Hallenbeck, Rick Dowling, Alex Skabardonis, and Shawn Turner. The authors acknowledge the contributions to this research from Weimin Huang, Kenny Voorhies, and Shawn Pope of Cambridge Systematics; Teresa Qu of the Texas Transportation Institute; David Reinke and Senanu Ashiabor of Dowling Associates; Herb Levinson; and Hesham Rakha. SHRP 2 STAFF Ann M. Brach, Director Stephen J. Andrle, Deputy Director Neil J. Pedersen, Deputy Director, Implementation and Communications Kizzy Anderson, Senior Program Assistant, Implementation James Bryant, Senior Program Officer, Renewal Kenneth Campbell, Chief Program Officer, Safety JoAnn Coleman, Senior Program Assistant, Capacity and Reliability Eduardo Cusicanqui, Financial Officer Walter Diewald, Senior Program Officer, Safety Jerry DiMaggio, Implementation Coordinator Shantia Douglas, Senior Financial Assistant Charles Fay, Senior Program Officer, Safety Carol Ford, Senior Program Assistant, Renewal and Safety Elizabeth Forney, Assistant Editor Jo Allen Gause, Senior Program Officer, Capacity Rosalind Gomes, Accounting/Financial Assistant Abdelmename Hedhli, Visiting Professional 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 Michael Marazzi, Senior Editorial Assistant Linda Mason, Communications Officer Reena Mathews, Senior Program Officer, Capacity and Reliability Matthew Miller, Program Officer, Capacity and Reliability Michael Miller, Senior Program Assistant, Capacity and Reliability David Plazak, Senior Program Officer, Capacity Monica Starnes, Senior Program Officer, Renewal Charles Taylor, Special Consultant, Renewal Onno Tool, Visiting Professional Dean Trackman, Managing Editor Pat Williams, Administrative Assistant Connie Woldu, Administrative Coordinator Patrick Zelinski, Communications/Media Associate

Reliability of transport, especially the ability to reach a destination within a certain amount of time, is a regular concern of travelers and shippers. The definition of reliability used in this research is how travel time varies over time. The variability can apply to the travel times observed over a road segment during a specific time slice (e.g., 3 to 6 p.m.) over a fairly long period of time, say a year. The variability can also pertain to the travel times of repeated trips made by a person or a truck between a given origin and destination. Agencies are increas- ingly aware of the issue of reliability, although the transportation industry as a whole as yet lacks a firm understanding of the causes and solutions to failures of reliability. As the agenda for the SHRP 2 research on travel time reliability took shape, it became clear a fundamental study was required to be able to talk about travel time reliability in a meaningful way. Basic reliability issues are addressed in this study, which is not concerned with average travel times, but rather ways of describing travel times that reflect the uncertainty in the amount of time required to travel between two points. Some of the uncertainty is systematic, such as the normal ebb and flow of traffic within the course of a work day or season of the year. Congestion associated with this systematic uncertainty is called recurrent. Congestion due to unpredictable or unexpected events is called nonrecurrent. Sources of nonrecurrent con- gestion include incidents (e.g., accidents), work zones, weather, special events, problems with traffic control devices, and unexpected fluctuations in demand. If every travel time observed over a highway section for a year is plotted, a distribution of travel time is obtained. This plotted distribution is the picture of travel time variability. Such distributions are the focus of this research, especially the degree to which recurring and nonrecurring congestion influence the nature of the distribution. This research shows how to derive performance measures from such distributions and recommends a set for use by managers, planners, and systems operators. The research reexamines the composition of the congestion puzzle in terms of the fractions attributable to recurrent and various sources of nonrecurrent congestion. The project team used before-and-after studies to determine the effectiveness of different types of actions, both operational and capacity improvements, in improving reliability. This study also examined the effect of the downturn of the economy on travel time reliability. Finally, this research resulted in two types of models that can be used to estimate or predict travel time reliability. These models have broad applicability to planning, programming, and systems management and operations. F O R EWO R D William Hyman, SHRP 2 Senior Program Officer, Reliability

C O N T E N T S 1 Executive Summary 1 Project Background 2 Project Approach 6 Findings 13 References 14 CHAPTER 1 Introduction 14 Significance of Travel Time Reliability on Transportation System Performance 14 New Concept of Travel Time Reliability 15 Defining Travel Time Reliability 15 Understanding Travel Time Reliability 15 Operational Strategies and Capacity Expansion 15 Travel Time Measurements 16 References 17 CHAPTER 2 Preparatory Analyses 17 Introduction 17 Literature Review 21 Improvements That Affect Reliability 21 Experimental Design 29 References 31 CHAPTER 3 Data Collection, Assembly, and Fusion 31 Introduction 31 Traffic and Travel Time Data 39 Incident and Work Zone Data 41 Weather Data 41 Geometric, Operating, and Improvement Data 41 Data Processing Procedures 43 Final Data Set for Statistical Analyses 45 Description of Seattle Study Area 49 References 50 CHAPTER 4 Empirical Measurement of Reliability 50 Overview 50 Recommended Reliability Metrics for the Research and General Practice 54 Travel Time Distributions and Reliability Performance Metrics 56 Data Requirements for Establishing Reliability 57 Trends in Reliability 61 Defining Peak Hour and Peak Period 61 Estimating Demand in Oversaturated Conditions on Freeways 63 Reliability Breakpoints on Freeways 67 Sustainable Service Rates on Freeways 71 Reliability of Signalized Arterials

74 Reliability of Rural Freeway Trips 74 Vulnerability to Flow Breakdown 77 Reliability of Urban Trips Based on Reliability of Links 79 Reference 80 CHAPTER 5 Estimating Congestion by Source: The Cause of Congestion 80 Introduction 80 Preliminary Look at Congestion by Source: Atlanta 81 A Closer Look at Congestion by Source: Seattle 120 References 121 CHAPTER 6 Before-and-After Studies of Reliability Improvements 121 Introduction 122 Results 123 References 124 CHAPTER 7 Cross-Sectional Statistical Analysis of Reliability 124 Potential Model Forms 126 Relationship Between Mean Travel Time and Reliability Metrics 142 Statistical Modeling of Reliability 150 Validation of Statistical Models 153 Reference 154 CHAPTER 8 Application Guidelines 154 Introduction 154 Selecting the Appropriate Relationship 154 Linking Improvements to Model Variables 158 Relationship Between Incident Management Efficiency and Model Variables 158 Induced Demand Effects of Improvements 161 References 163 CHAPTER 9 Conclusions and Recommendations 163 Findings and Products of the Research 169 Recommendations for Future Research 171 Reference 172 Appendix A. Data Elements and Structure for the Statistical Analysis Data Set 177 Appendix B. Before-and-After Analyses of Reliability Improvements 217 Appendix C. Computation of Influence Variables, Seattle Analysis: Mechanisms for Determining When an Incident Affects Travel Time and Travel Time Reliability 221 Appendix D. Seattle Analysis: Variable Definitions 229 Appendix E. Summary of Weather Data Tests: Seattle Analysis 245 Appendix F. Statistics Related to the End of Congestion: Seattle Analysis 250 Appendix G. Computation of Travel Time Metrics 253 Appendix H. Revised Data-Poor Equations Online version of this report: www.trb.org/Main/Blurbs/166935.aspx.