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cisco tour- based model can be used to predict travel by San Francisco County residents, while the BAYCAST model can be used to predict travel by residents from the other eight counties. Figure 1 presents a schematic diagram of SF- CHAMP. This diagram includes the model components and data inputs for these components. A synthesized population of San Francisco residents is input into each model component to estimate choices for work loca- tion; vehicle availability; and tours and trips by time of day, destination, and mode of travel. The synthesized tours and trips are aggregated to represent flows between traffic analysis zones before traffic assignment. A separate model of visitor travel is estimated so as to incorporate trips made by tourists and business travel- ers visiting San Francisco County. The model system also incorporates trips made by non- San Francisco resi- dents by merging regional trip tables into the process for assignment. Limitations of Approach There were a few limitations of this approach that were a result of the available time and resources of the project: ⢠Initially, there was no onboard survey data avail- able for validation of the mode choice model. There was a discrepancy between the U.S. Census journey- to- work data and the observed transit boarding data; this dis- crepancy could not be resolved without the additional onboard survey data. These onboard survey data were collected in the spring of 2006 and are being used to update the mode choice model now. ⢠The resources for the peak- spreading model were limited in the original project, and, as a result, a peak- spreading model was transferred from the MTC rather than estimated for San Francisco. This transfer did not produce reliable results and was not used in any plan- ning applications. Subsequently, the FHWA funded a 25THE SAN FRANCISCO MODEL IN PRACTICE Full-Day Tour Pattern Models Time of Day Models Workplace Location Model Vehicle Availability Model Nonwork Tour Destination Choice Models Tour Mode Choice Models Intermediate Stop Choice Models Trip Mode Choice Models Highway Assignment by Time Period (5) Transit Assignment by Time Period (5) Visitor Trip Mode Choice Model Visitor Trip and Destination Choice Model Logsum Variables Accessibility Measures Zonal DataPopulationSynthesizer Regional Trip Tables for NonSF Trips Logsum Variables All Models Network Level of Service All Remaining Models Trip Diary Records Person Records Trip Tables FIGURE 1 Model components.
