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Metropolitan Travel Forecasting: Current Practice and Future Direction

The committee assesses travel demand forecasting and identifies shortcomings in travel forecasting models, obstacles to better practice, and actions needed to ensure the use of appropriate technical approaches

Preface

Metropolitan planning organizations (MPOs) develop regional transportation plans and programs to accommodate mobility needs within their regions. This process is commonly performed with the assistance of computerized travel demand models that provide information on current and future transportation system operations.

In 2003, the Transportation Research Board (TRB) of the National Research Council (NRC) conducted a peer review of the travel demand modeling of the Metropolitan Washington Council of Governments’ (MWCOG) Transportation Planning Board (TPB), the MPO for Washington, D.C. In the course of this review, it became apparent that little information is available to practitioners to assist them in making judgments about state-of-the-practice techniques for model development and application. Although the NRC committee that conducted the review was charged with assessing whether the modeling of the MWCOG TPB was state of the practice, the committee had to rely on its judgment in making this assessment, rather than on detailed information about how key technical issues are treated by the MPO’s peers.

In this context, the Federal Highway Administration (FHWA), the Federal Transit Administration (FTA), and the Office of the Secretary of Transportation (OST) funded a new TRB study to gather information needed to determine the national state of practice in metropolitan area travel demand forecasting by MPOs and state departments of transportation (DOTs). The statement of task for this study comprised three main elements: (1) description of the current state of practice in metropolitan travel forecasting; (2) evaluation of the current state of practice, including any deficiencies; and (3) recommendations for improvement. This main report responds to each part of these elements, although it emphasizes the latter two. In addition, a companion technical report commissioned for this study provides supporting detail on current MPO modeling practice, but the reader should not need to consult that report for a broad understanding of the committee’s findings and recommendations. The detailed charge to the committee may be found in Appendix B, Committee Statement of Task.

To conduct this study, TRB formed a committee chaired by Martin Wachs, then director of the Institute of Transportation Studies at the University of California, Berkeley, and currently director of the RAND Corporation’s Transportation, Space, and Technology Program. The 12 committee members brought to the study expertise in four broad areas: the relationship of travel forecasting to public policy and planning, the development of applied travel forecasting models, the application of travel forecasting models, and independent academic research on travel forecasting. In addition, committee members were expert in key areas of interest, including land use planning and modeling, air quality emissions estimates, transit modeling, and data collection and analysis.

The committee supplemented its own expertise by seeking technical guidance from three corporations that were responsible for much of the model development in U.S. metropolitan areas: PB Consult, Inc., Cambridge Systematics, Inc., and AECOM.

To gather the detailed information on travel modeling practice needed to respond to its charge, the committee employed a consulting firm, BMI-SG, Inc. (subsequently VHB, Inc.). The consultant conducted a web-based survey of modeling practice among all MPOs. Responding to this survey were 60 percent of all MPOs and 84 percent of those with more than 1 million population. The consultant also conducted an extensive literature review, as well as in-depth interviews at 16 MPOs or state DOTs that perform modeling for MPOs in their state.

To be further advised on topics relating to the study, the committee requested and received at its meetings presentations from staff of FHWA; FTA; OST; the Environmental Protection Agency; the Association of Metropolitan Planning Organizations (AMPO); the American Association of State Highway and Transportation Officials’ (AASHTO) Standing Committee on Planning; Environmental Defense; and the TRB Committee on Transportation Planning Applications. Particular topics on which the committee asked to be briefed were FTA’s New Starts program, FHWA’s TRANSIMS modeling initiative, and FHWA’s Freight Models Improvement Program. In addition, the committee held a joint meeting with the AMPO Travel Models Working Group to discuss the initial findings of the above web-based survey of MPO modeling practice.

The committee deliberated carefully as to the intended audience for its report. It concluded that the primary audience for this main report, with its findings and recommendations, should be those with a broad interest in metropolitan transportation planning, programming, and policy making, such as MPO policy board members. The committee was well aware that travel forecasting is a complex topic, with specialized concepts and language that may not be accessible to that primary audience. It therefore attempted to ensure that this main report would be largely nontechnical; where technical modeling terms are used, they are explained.

This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by NRC’s Report Review Committee. The purpose of this independent review is to provide candid and critical comments that assist the authors and NRC in making the published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The contents of the review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. The committee thanks the following individuals for their participation in the review of this report: Elizabeth A. Deakin, University of California, Berkeley; Mark E. Hallenbeck, University of Washington, Seattle; Lester A. Hoel, University of Virginia; Charles E. Howard, Jr., Puget Sound Regional Council; Keith L. Killough, Southern California Association of Governments; Ronald F. Kirby, Metropolitan Washington Council of Governments; Frank S. Koppelman, Northwestern University; and T. Keith Lawton, Keith Lawton Consulting, Inc.

Although the reviewers listed above provided many constructive comments and suggestions, they were not asked to endorse the committee’s conclusions or recommendations, nor did they see the final draft of the report before its release. The review of this report was overseen by Adib K. Kanafani, University of California, Berkeley; and C. Michael Walton, University of Texas at Austin. Appointed by NRC, they were responsible for making certain that an independent examination of the report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.

Jon M. Williams of TRB managed the Study and drafted the final report under the guidance of the committee and supervision of Stephen R. Godwin, Director of Studies and Special Programs at TRB. Suzanne Schneider, Associate Executive Director of TRB, managed the report review process. Frances Holland and Amelia Mathis assisted with meeting arrangements and communications with committee members. Rona Briere edited the report, Alisa Decatur prepared the edited manuscript, and Jennifer Weeks, TRB Editorial Services Specialist, prepared the prepublication report for web posting.