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OCR for page 35
The San Francisco Model in Practice
Validation, Testing, and Application
Maren L. Outwater, Cambridge Systematics
Billy Charlton, San Francisco County Transportation Authority
T
he San Francisco County Chained Activity Model- a person's travel across the day. This approach includes
ing Process (SF-CHAMP) was developed for the San the frequency of five types of tours:
Francisco County Transportation Authority
(SFCTA) to provide detailed forecasts of travel demand for · Home-based work primary tours,
various planning applications (1). These applications · Home-based education primary tours,
included developing countywide plans, providing input · Home-based other primary tours,
to microsimulation modeling for corridor and project- · Home-based secondary tours, and
level evaluations, transit planning, and neighborhood · Work-based subtours.
planning. The objective was to represent accurately the
complexity of the destination and the temporal and A home-based tour includes the entire chain of trips
modal options and to provide detailed information on made between leaving home and arriving back at home.
travelers making discrete choices. These objectives led to The primary home-based tour is defined as the main
the development of a tour-based model that uses synthe- home-based tour made during the day. If a worker makes
sized population as the basis for decision making rather a work tour or a student makes an education tour, then
than zonal-level aggregate data sources. that is always the primary tour. If there are no work or
Most of the tour-based model's nine components were education tours, the primary tour is the tour with the
estimated by means of household survey data for San highest-priority activity at the destination (shop-
Francisco, California, residents only that were collected pingpersonal business followed by socialrecreation
by the Metropolitan Transportation Commission followed by serve passenger). If there are two or more
(MTC). Each model component was calibrated by using tours with the same activity priority, then the one with
various observed data sources, and then the full model the longest duration of stay at the destination is the pri-
was validated with traffic count and transit ridership mary tour. All other home-based tours are designated as
data for each of five periods. The model is applied as a secondary tours. A special type of tour is a work-based
focused model that combines trip making from the entire subtour, defined as the entire chain of trips made
Bay Area (derived from the MTC's BAYCAST trip tables) between leaving the primary workplace and returning to
with the travel demand from San Francisco residents that workplace in the same day. By using tours as a key
produced by the tour-based model. unit of travel, the interdependence of different activities
in a trip chain is captured. This method provides a better
understanding of non-home-based trips, especially in the
ORIGINAL APPROACH AND LIMITATIONS case of the work-based subtours that represent a signifi-
cant proportion of non-home-based travel.
Modeling Process The study area for the model is the nine-county San
Francisco Bay Area, which is represented by the MTC's
The main feature of the full-day pattern approach is that regional travel demand forecasting model, BAYCAST.
it simultaneously predicts the main components of all of The study area is divided into two parts, so the San Fran-
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