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1 Introduction E very urban area in the United States with a population of 50,000 or more must have a metropolitan transportation planning process as a precondition for federal funding of transportation projects (23 USC 134 and 49 USC 5303). A metropolitan planning organization (MPO), designated by agreement between the governor and units of general-purpose local government representing at least 75 percent of the affected population, is responsible for leading this planning process. An MPO is a transportation policy-making body composed of representative local elected officials, repre- sentatives of public transportation agencies, and appropriate state officials. OVERVIEW OF TRAVEL FORECASTING A key element of transportation planning is the evaluation of alternative operating and capital investment strategies. This process requires estimates of current and forecasts of future travel on the surface transportation system, including highway, transit, nonmotorized, and freight modes. These travel forecasts are generally accomplished through computerized network simula- tions of the transportation system, known as travel demand forecasting mod- els. Such models are highly complex and require as inputs extensive current information on roadway and transit system characteristics and operations, as well as current and forecast demographic information. Creating and operat- ing the models requires a high degree of technical training and expertise. Travel forecasting models are used to study proposed investments in the transportation system and to determine which of those investments will best serve the publicâs needs for future travel and economic development. The models are also used to evaluate the travel impacts of alternative land use 15
METROPOLITAN TRAVEL FORECASTING Current Practice and Future Direction 16 scenarios. The model outputs are used as well to determine the air pollu- tants due to automobiles, trucks, and buses and thus the air quality impacts of proposed transportation projects. The work of MPOs is under increasing scrutiny by stakeholders, includ- ing local elected officials, state transportation agencies, federal agencies with resource allocation and regulatory responsibilities, bond financiers, the busi- ness community, the environmental community, and the traveling public. Different stakeholders may propose or support differing transportation invest- ments and outcomes, and travel forecasts provide them with important sup- porting information. Some MPOs have even faced legal action or the threat of such action against their transportation planning process based on the quality of their travel forecasts. According to a recent study, âAlthough travel demand models have been used in transportation planning for some four decades, there are few universally accepted guidelines or standards of practice for these models or their applicationâ (TRB 2003). As a result, metropolitan area and project-level travel forecasts and the models that produce them often become the object of intense public debate, and agencies need to have a means of showing they are doing credible work. Metropolitan travel forecasting models that produce reliable and broadly accepted forecasts allow elected officials to weigh the competing needs of stakeholders and make informed decisions about optimal investments of pub- lic funds. On the other hand, when models are supplied with inaccurate or out-of-date data, are poorly specified, or are not competently applied, they may produce poor forecasts that contribute to planning failures. Such fail- ures include wasting public funds on transportation facilities that are over scale or not warranted at all, building facilities that are under scale and do not meet near-term demand, and conducting air quality planning that fails to achieve emission reduction targets. The consequences of planning failures include new passenger rail systems that are underutilized and therefore require unexpected funding for operations, new toll facilities that are underutilized and cannot meet operational costs and bonding debt service, freeway expan- sions that are completely congested a few years after opening, and the public health effects of air pollution. For these reasons, MPOs require the best available travel forecasting processes. In the absence of practice guidelines, MPOs need information on the cur- rent state of travel demand forecasting to best satisfy federal, state, and local requirements; to provide elected officials with a sound basis for informed deci- sion making; to assure interested stakeholders of the quality of the forecasting
Introduction 17 process; and to avoid the consequences of poor forecasts. Moreover, there is a growing consensus that metropolitan travel forecasting might be improved through and could benefit from the identification of current best practices for differing metropolitan settings and applications. This report is intended to respond to these needs. REPORT ORGANIZATION AND APPROACH Modeling and forecasting of metropolitan travel demand are founded on a set of complex and evolving technical tools and methods, often described in a highly specialized language. Metropolitan travel forecasting has the intended purpose of providing vital information to inform policy and programming decisions. The subject therefore holds great interest for both those engaged in the technical aspects of travel forecasting and those using the resulting fore- casts for decisions on transportation capital investments and policies. This report is intended for a broad audience of transportation planners, policy makers, and technical experts. It necessarily includes discussion of travel forecasting processes but at a conceptual level, using nontechnical language and explaining the meaning of technical terms that must be employed. The committeeâs findings and recommendations are summarized at the beginning of the report. The remainder of the report provides a brief history and overview of metro- politan transportation planning and travel forecasting (Chapter 2); a descrip- tion of the institutional framework for travel forecasting (Chapter 3); a review of the current state of modeling and forecasting practice derived from a liter- ature review, a web-based survey, and interviews (Chapter 4); a discussion of the shortcomings of current forecasting processes (Chapter 5); a review of recent advances in the state of practice (Chapter 6); and a discussion of the pace of change and innovation. Chapters 2 through 6 conclude with a brief summary of the key findings and the committeeâs recommendations found in each chapter. The committee also wished to meet the needs of those with a primary inter- est in the technical aspects of metropolitan travel forecasting, and much of the information gathered and distilled for this study may be of value to the technician. Therefore, the full consultant technical report on MPO modeling practices commissioned for this study has been provided as an electronic annex to this report, available at http://onlinepubs.trb.org/onlinepubs/reports/ VHB-2007-Final.pdf (VHB 2007).
METROPOLITAN TRAVEL FORECASTING Current Practice and Future Direction 18 REFERENCES Abbreviation TRB Transportation Research Board TRB. 2003. Letter Report from TRB Committee for Review of Travel Demand Modeling by the Metropolitan Washington Council of Governments. Transportation Research Board of the National Academies, Washington, D.C., Sept. 8. http://onlinepubs.trb. org/onlinepubs/reports/mwcogsept03.pdf. VHB. 2007. Determination of the State of the Practice in Metropolitan Travel Forecasting: Findings of the Surveys of Metropolitan Planning Organizations. Transportation Research Board of the National Academies, Washington, D.C. http://onlinepubs.trb. org/onlinepubs/reports/VHB-2007-Final.pdf.
