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13 BREAKOUT SESSION Tour- Based Models Mark Bradley, Mark Bradley Research and Consulting John Bowman, John Bowman Research and Consulting Peter Vovsha, PB Consult, Inc. Kuo- Ann Chiao, New York Metropolitan Transportation Council Maren Outwater, Cambridge Systematics, Inc. Billy Charlton, San Francisco Transportation Authority David Schmitt, AECOM Consulting Rebekah Anderson, Ohio Department of Transportation DESIGN FEATURES OF ACTIVITY- BASED MICROSIMULATION MODELS FOR U.S. METROPOLITAN PLANNING ORGANIZATIONS Mark Bradley and John Bowman Mark Bradley discussed the design features of activity- based models recently developed or implemented at selected metropolitan planning organizations (MPOs) throughout the country. The metropolitan areas exam- ined included Portland, Oregon; San Francisco; Sacra- mento; New York; Columbus, Ohio; Atlanta; and Denver. Volume 2 includes a paper on this topic.1 The following points were covered in the presentation. ⢠The activity- based models in the seven areas are in different stages of development, implementation, and use. The Portland model was developed in the late 1990s and has been used in a number of studies, including examining road pricing options. The San Francisco model and the New York model were implemented after Portland. The Sacramento model is being implemented. The Atlanta model is in the estimation stages. The design stages of the Denver and the San Francisco Bay Area models are just being completed and the estimation stages are beginning. ⢠The activity- based models examined share a simi- lar overall structure, with a hierarchy of levels. They are all microsimulation based, simulating people and house- holds one at a time. The models also produce trips that go into an aggregate equilibrium assignment. The assign- ment procedure is the same as in the four- step modeling process. The process for trips going into the model assignment is different, however. At the bottom level are trips and stops, which are similar to trip- based models. The second level, which includes tour- level decisions, and the third level, which includes person- day decisions and household- day decisions, are different. The top level of longer- term household and person- level decisions is also different. This level includes decisions related to work, school, and automobile ownership. There are important design features that distinguish the different models. ⢠All of the model systems simulate persons one- by- one and require a representative sample of households and persons for the base year and a given forecast year. Most of the models use a synthetic sample, which repre- sents every person in the population in a given forecast year. Most areas use three variables to design and con- struct the sample for every zone. These variables are household size, number of workers in the household, and household income. Other variables used in some models include the age of the head of the household, the presence of children under 18 years of age, the presence of adults over 65 years of age, and family and nonfamily households. Race and ethnicity are being added to the San Francisco model. 1 See Bradley, M., and J. Bowman. Design Features of Activity- Based Microsimulation Models for U.S. Metropolitan Planning Organizations: A Summary. In Conference Proceedings 42: Innovations in Travel Demand Modeling, Volume 2: Papers, Transportation Research Board of the National Academies, Washington, D.C., 2008, pp. 11â20.
