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OCR for page 36
THE SAN FRANCISCO MODEL IN PRACTICE 25
cisco tour-based model can be used to predict travel by Limitations of Approach
San Francisco County residents, while the BAYCAST
model can be used to predict travel by residents from the There were a few limitations of this approach that were
other eight counties. a result of the available time and resources of the project:
Figure 1 presents a schematic diagram of SF-
CHAMP. This diagram includes the model components · Initially, there was no onboard survey data avail-
and data inputs for these components. A synthesized able for validation of the mode choice model. There was
population of San Francisco residents is input into each a discrepancy between the U.S. Census journey-to-work
model component to estimate choices for work loca- data and the observed transit boarding data; this dis-
tion; vehicle availability; and tours and trips by time of crepancy could not be resolved without the additional
day, destination, and mode of travel. The synthesized onboard survey data. These onboard survey data were
tours and trips are aggregated to represent flows collected in the spring of 2006 and are being used to
between traffic analysis zones before traffic assignment. update the mode choice model now.
A separate model of visitor travel is estimated so as to · The resources for the peak-spreading model were
incorporate trips made by tourists and business travel- limited in the original project, and, as a result, a peak-
ers visiting San Francisco County. The model system spreading model was transferred from the MTC rather
also incorporates trips made by non-San Francisco resi- than estimated for San Francisco. This transfer did not
dents by merging regional trip tables into the process for produce reliable results and was not used in any plan-
assignment. ning applications. Subsequently, the FHWA funded a
Population Zonal Data
Synthesizer
Person Records All Models
Workplace Vehicle Availability
Location Model Model
Full-Day Tour Accessibility
Pattern Models Measures
Time of Day
Models
Logsum
Variables Nonwork Tour Network
Destination Choice Level of Service
Models
Logsum
Trip Diary Records Variables All Remaining
Models
Tour Mode Choice
Models
Intermediate Stop Visitor Trip and
Choice Models Destination Choice
Model
Regional Trip
Tables for NonSF Trip Mode Choice Visitor Trip Mode
Trips Models Choice Model
Trip Tables Transit Highway
Assignment by Assignment by
Time Period (5) Time Period (5)
FIGURE 1 Model components.
