Travel models for small urban areas: A forensic assessment
Date
1997
Authors
Vodrazka, Walter Charles
Major Professor
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Souleyrette, Reginald
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Abstract
Travel demand models provide estimates of future traffic volumes for roadway networks. Models incorporate intended land use, socio-economic and demographic characteristics, and the availability and quality of transportation services to generate traffic forecasts for a horizon year. These forecasts are used by transportation planners as an important input to the planning and programming of roadway and transit improvements. Since transportation funds are limited, policy makers and elected officials require accurate information as a basis for transportation improvement decisions.
Recent legislation has prompted the need to improve the travel demand forecasting process. The suggested improvements and much of the research is devoted to large metropolitan areas or areas designated by the Environmental Protection Agency to be in nonattainment of the Clean Air Act Amendments (CAAA) standards. Of these improvements, few are applicable to small urban areas and none of the reviewed literature has determined the effectiveness of the forecasting process through an evaluation of case studies.
This research did not attempt to identify the deficiencies of the modeling process or the proposed improvements. Rather, this research focused on an evaluation of the modeling process to determine the ability of the conventional four-step sequential modeling process to meet the needs of small urban area planning. Therefore, the scope of the study was limited to small urban areas under 50,000 population presently in attainment of CAAA standards. Two Iowa case studies, the Ames Urban Area Transportation Planning Study and the Marshalltown Area Transportation Planning Study, were analyzed. The evaluation was based on the estimation of the number of lanes needed on the roadway network. The research involved not only evaluating previously developed models, but also reconstructing the models to obtain the horizon-year assigned traffic volumes. The case studies showed that the conventional four-step modeling process is able to meet the needs of small urban area planning. The number of lanes required by the actual traffic counts was estimated correctly for 95.9 percent of the links on the Ames model and for 96.9 percent of the links on the Marshalltown model.
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