Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. FHWA/TX-12/0-6632-1 4. Title and Subtitle 5. Report Date POSITIVE FEEDBACK: EXPLORING CURRENT APPROACHES IN October 2011 ITERATIVE TRAVEL DEMAND MODEL IMPLEMENTATION Published: January 2012 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Phillip Reeder, Chandra Bhat, Karen Lorenzini, and Kevin Hall Report 0-6632-1 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Texas Transportation Institute The Texas A&M University System 11. Contract or Grant No. College Station, Texas 77843-3135 Project Number 0-6632 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Texas Department of Transportation Technical Report: Research and Technology Implementation Office September 2010–August 2011 P.O. Box 5080 14. Sponsoring Agency Code Austin, Texas 78763-5080 15. Supplementary Notes Project performed in cooperation with the Texas Department of Transportation and the Federal Highway Administration. Project Title: Positive Feedback: An Examination of Current Approaches in Iterative Travel Demand Model Implementation URL: http://tti.tamu.edu/documents/0-6632-1.pdf 16. Abstract Currently, the models that TxDOT’s Transportation Planning and Programming Division (TPP) developed are traditional three-step models (i.e., trip generation, trip distribution, and traffic assignment) that are sequentially applied. A limitation of this sequential approach is an inconsistency between the travel time data used in the different stages of the process that may result in: (1) TDMs, which do not accurately reflect system-wide or corridor-level travel patterns, (2) travel times in alternative analyses that may not reflect accurate results, and (3) inaccurate results being used for the air quality determination process. To resolve these differences in the model sequence, researchers proposed an iterative feedback mechanism as an approach. This project researched current trends, practices, and tools in implementing a feedback approach for potential implementation in the TxDOT TDMs. In general, past research and practice underscores the importance of incorporating feedback loops in the travel demand process, especially in regions with moderate to high levels of traffic congestion during certain times of the day. Since the current TxDOT TDM model does not include any impedance or accessibility measures in the trip generation step, the best current approach is to feed back the output from the traffic assignment step to the trip distribution step. Overall, critical consideration should be given to the relative impact that implementing feedback might have on existing TxDOT-TPP practices. A feedback mechanism necessarily includes additional training and increases the calibration time associated with delivering base year travel models; and possibly could include additional data processing (and collection) related to time-of-day implementation. 17. Key Words 18. Distribution Statement Travel Demand Model, Feedback, Trip Distribution, Trip No restrictions. This document is available to the public Assignment through NTIS: National Technical Information Service Alexandria, Virginia 22312 http://www.ntis.gov 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 158 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized POSITIVE FEEDBACK: EXPLORING CURRENT APPROACHES IN ITERATIVE TRAVEL DEMAND MODEL IMPLEMENTATION by Phillip Reeder Program Manager, Travel Forecasting Program Texas Transportation Institute Chandra Bhat Adnan Abou-Ayyash Centennial Professor in Transportation Engineering University of Texas at Austin Karen Lorenzini Associate Research Engineer Texas Transportation Institute and Kevin Hall Research Scientist Texas Transportation Institute Report 0-6632-1 Project 0-6632 Project Title: Positive Feedback: An Examination of Current Approaches in Iterative Travel Demand Model Implementation Performed in cooperation with the Texas Department of Transportation and the Federal Highway Administration October 2011 Published: January 2012 TEXAS TRANSPORTATION INSTITUTE The Texas A&M University System College Station, Texas 77843-3135 DISCLAIMER This research was performed in cooperation with the Texas Department of Transportation and the Federal Highway Administration. The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official view or policies of the Federal Highway Administration or the Texas Department of Transportation. This report does not constitute a standard, specification, or regulation. The United States Government and the State of Texas do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the object of this report. v ACKNOWLEDGMENTS This project was conducted in cooperation with the Texas Department of Transportation (TxDOT) and the Federal Highway Administration (FHWA). The Texas Transportation Institute in cooperation with the Center for Transportation Research performed the research reported here. Mr. Greg Lancaster, Team Lead, Transportation Planning and Programming Division, TxDOT, served as the research project director. The authors thank the members of the Project Monitoring Committee for their advisement and guidance: • Janie Temple, Transportation Planning and Programming Division, TxDOT. • James Burnett, Transportation Planning and Programming Division, TxDOT. • Laura Norton, Transportation Planning and Programming Division, TxDOT. • George Petrek, Transportation Planning and Programming Division, TxDOT. Special thanks to Duncan Stewart and Frank Espinosa of TxDOT’s Research and Technology Implementation (RTI) Division for their assistance in this project. The authors thank the following individuals from TTI for their assistance: • Mr. Justin Malnar–contract assistance. • Editors in TTI’s Communications Division. vi TABLE OF CONTENTS Page List of Figures ............................................................................................................................... ix List of Tables ................................................................................................................................. x Introduction ................................................................................................................................... 1 Background ................................................................................................................................. 1 Chapter 1. State of Practice in Feedback Implementation ..................................................... 9 Introduction ................................................................................................................................. 9 Dimensions of the Feedback Process ........................................................................................ 11 The Feedback Process in Practice ............................................................................................. 18 Chapter Summary ..................................................................................................................... 23 Chapter 2. Potential Issues with Implementing Feedback as Part of the TxDOT TDM Process ................................................................................................................... 25 Overview of TxDOT Software ................................................................................................. 25 Trip Generation (TripCAL5) .................................................................................................... 28 Network Specification .............................................................................................................. 31 Trip Distribution (ATOM2) ...................................................................................................... 49 Traffic Assignment ................................................................................................................... 53 Impedance Adjustment Factor .................................................................................................. 54 Chapter Summary ..................................................................................................................... 67 Chapter 3. State-of-the-Art Future Development Trends for Feedback Implementation ............................................................................................................... 71 Introduction ............................................................................................................................... 71 Feedback Approaches in the Context of Possible Medium-Term Changes in TxDOT’s TDM .............................................................................................................................. 71 Feedback Approaches in the Context of Possible Long-Term Changes in TxDOT’s TDM .............................................................................................................................. 74 Chapter Summary ..................................................................................................................... 76 Chapter 4. Sensitivity Analysis and Field Test ......................................................................