Metropolitan Travel Forecasting Current Practice and Future Direction -- Special Report 288 (2007) / Chapter Skim
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2 Forecasting Metropolitan Travel
2 Forecasting Metropolitan Travel
Pages 19-34
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HISTORICAL CONTEXT Metropolitan Transportation Planning America's cities lie within larger metropolitan regions that comprise a patchwork of local governments. The Boston metropolitan region, for example, includes 101 local governments; San Francisco, 111; and Chicago, 274.
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According to this act: After July 1, 1965, the Secretary shall not approve under section 105 of this title any programs for projects in any urban area of more than fifty thousand population unless he finds that such projects are based on a continuing, comprehensive transportation planning process carried out cooperatively by states and local communities in conformance with the objectives stated in this section. The act laid the foundation for the current metropolitan transportation plan ning process and led to the establishment of metropolitan planning organiza tions (MPOs)
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MPOs are governed by policy boards comprising local elected officials and representatives of public transportation agencies and relevant state agencies. MPOs therefore represent a partnership among the federal government, state governments, and local governments, created to ensure that a continuing, comprehensive, and cooperative transportation planning process is in place in each metropolitan area.
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As public ownership of and investment in transit increased in the 1960s and 1970s, more sophisticated models were developed to better represent transit and high-occupancy vehicle alternatives. By the 1990s, commercial transportation planning software for microcomputers had largely replaced federally supported transportation planning software for mainframes, but the commercial software retained similar modeling methods and approaches.
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This entire process is termed "travel demand forecasting" or the "four-step process." The metropolitan travel demand forecasting process was born of necessity in the postwar era during a time of major capital investment in inter- and intracity transportation systems. The process grew in a piecemeal manner as a linked chain of submodels, each designed to solve a particular problem associated with the ultimate goal -- forecasting future travel to assist in planning the size and location of new and expanded highway and transit facilities.
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In addition, MPOs in federally designated air quality nonattainment and maintenance areas must determine whether their regional transportation plans and programs conform to state air quality implementation plans (SIPs) for meeting national air quality standards.2 This transportation conformity evaluation requires MPOs to use forecasts for their Transportation Improve ment Program and long-range plan to estimate traffic volumes and speeds, which become inputs to the Environmental Protection Agency's (EPA's)
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The most commonly used metropolitan travel forecasting models represent the interactions among demand, supply, and price in a combined regional travel demand model. More advanced modeling practice may require interfaces with separate supply models to provide detailed information on such transportation system characteristics as speeds, volumes, congestion, delay, and traffic by time of day.
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EXPANDED REQUIREMENTS FOR METROPOLITAN TRAVEL MODELING MPOs today face a much broader and more complex set of requirements and needs in their travel modeling than they did in the 1960s and 1970s, when the primary concern was evaluating highway and transit system capacity expansions. Some of the most salient of these requirements and the demands they make on modeling practice are discussed below.
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Land Use Policies Many growing regions must consider options other than transportation capital improvements for addressing future mobility needs. Their MPOs therefore need to be able to model land use policies such as increases in overall density, urban growth boundaries, intensification around rail stations, and more mixed housing and employment.
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Thus, a model that does not address these modes fails to account for a substantial market share of the region's travel. Transportation Policies Air quality nonattainment areas must pay increased attention to travel demand management as a means of reducing vehicle emissions.
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Urban models represent an opportunity to measure changes in the economy in much more inclusive ways. Metropolitan regions and states that use commodities movement models with a modechoice step can obtain a more accurate version of the economic benefits of alternative transportation investments because these models represent the costs of goods movement more accurately.
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Planning for Emergencies Travel models are increasingly being employed to plan evacuations due to natural disasters, to plan immunization programs, and to conduct risk assess ments related to homeland security. The events of September 11, 2001, exemplify the need for these new modeling applications and, in turn, the need to develop new modeling practices and data that are appropriate for emergency planning.
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Following World War II, the federal government showed increasing interest in addressing urban issues through regional councils. The Housing Act of 1961 and the Federal-Aid Highway Act of 1962 laid the foundation for the current metropolitan transportation planning process and led to the establishment of MPOs for every urbanized area in the country.
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They must now account for or evaluate such issues as the following: • Motor vehicle emissions and vehicle speeds; • Induced travel; • Alternative land use policies; • Nonmotorized travel (walking and bicycling) ; • Transportation policies, such as congestion pricing; • Cumulative and secondary impacts of transportation facilities; • Environmental justice, or avoiding disproportionate adverse impacts on low-income and minority households or disproportionate distribution of benefits; • Economic development; • Emergencies due to weather, health, or threats to homeland security; and • Demographic changes.
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2001. Urban Transportation Planning: A Decision-Oriented Approach.
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1999. Urban Transportation Planning in the United States.
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