travel demand forecasting report - Sonoma County Transportation ...

Appendix I: Travel Demand Forecasting Report
choice model considers projected levels in 2025 for all key variables that influence travel demand.
These variable considerations include population, households, employment, income, and auto
ownership, as well as highway network characteristics (i.e. link capacities and speeds, centroid
characteristics, and HOV facilities) and transit system characteristics (i.e. bus and rail routes, stations,
and frequency). These major inputs into the travel demand model are discussed in the following
sections and chapters.
2.2 System-Wide Flow of Trips
The Year 2025 trip tables for the study area were held constant; therefore the origins and destinations of
the trips remain constant across alternatives. This section describes the major trip movements for the
home-based work (HBW) trips related to the SMART study area. As mentioned, the model is comprised
of nine counties. These counties are further divided into 34 superdistricts. The six superdistricts
corresponding to Sonoma and Marin were combined to represent each county. To understand systemwide
HBW trip movement, desire lines were created between each county in the SMART study area to
every super-district in the remaining counties.
Figures 2.2-1 and 2.2-2 display Year 2025 desire lines representing two-way flow of HBW person trips
for Sonoma County and Marin County, respectively. The blue lines indicate trip productions while the
green lines indicate trip attractions. The tables of total home-based work person trips between superdistricts,
which were used to create these desire lines for each SMART county, are displayed in
Appendix A and Appendix B. Figure 2.2-1 shows the flows to and from Sonoma County (Superdistricts
29) in 2025. The main flow of HBW trips is to/from Marin County, followed by flows to San Francisco
(Superdistrict 1), and from Napa (Superdistrict 27). Figure 2.2-2 shows the 2025 flows to and from Marin
County (Superdistrict 32) in 2025. The major flow of trips is to San Francisco (Superdistrict 1), followed
by major flows to and from Sonoma County (Superdistricts 29 and 30).
Table 2.2-1 is a subset of the super-district to super-district table which focuses on 2025 trips associated
with the SMART corridor going to/from the other super-districts. As shown in Table 2.2-1, 446,000 work
trips originate in Sonoma County of which over 365,000 trips (or 82 percent) remain inside the county,
the next highest area for Sonoma County work trip destinations is Marin County (Superdistricts 30-32)
with nearly 40,000 daily trips, followed by San Francisco (Superdistrict 1) with approximately 12,000 daily
trips. The super district with the most work trips destined to Sonoma County is from Napa County
(Superdistrict 27), with over 14,000 daily trips. It is followed by Marin County, Superdistricts 30 and 31,
which produces a combined flow of about 17,000 daily trips destined to Sonoma County.
As observed in Table 2.2-1, like Sonoma County the majority of work trips remain inside the county of
origin, Marin, which generates over 125,000 daily trips. However, from Marin approximately 55,000 (22
percent) of work trips are attracted into San Francisco Superdistrict 1, and approximately nine percent
travel to Sonoma County Superdistricts 29-31.
It is evident from the desire lines that the majority of the HBW trips in the study area remains within the
origin County or travel to the other County. This, coupled with the congestion on Highway 101, suggest
a need for travel within and between the counties.
Sonoma-Marin Area Rail Transit 4 Travel Demand Forecasting Report
September 2005