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OCR for page 45
34 I N N O VAT I O N S I N T R AV E L D E M A N D M O D E L I N G , V O L U M E 2
Zonal Accessibility
Daily Activity Pattern / Tour Production
Log-sums for
representative
TOD periods
Primary Tour Destination
Log-sums for
all TOD periods
Time-of-Day by Half-Tours
Highway & best
Entire-Tour Mode / Best Transit Sub-mode transit skims
Log-sums
Stop Frequency by Half-Tours
Access by best
Stop Location transit sub-mode
Transit sub-mode skims
Trip Mode
Traffic & Transit Assignment
FIGURE 1 General structure of the MORPC model system.
high-occupancy vehicle; 3, walk to transit; 4, drive to After processing through all tour-level and trip-level
transit; 5, nonmotorized; or 6, school bus), and which stages, trip tables are constructed for all modes and tran-
one of five transit submodes is chosen for each half tour sit submodes. These tables are assigned to the corre-
for walk-to-transit and drive-to-transit tours [1, local sponding highway and transit subnetworks. Loaded
bus; 2, express bus; 3, bus rapid transit; 4, light rail tran- networks are skimmed to produce level-of-service attri-
sit (LRT); or 5, commuter rail]; and butes necessary for the models. The model system is
· Stop-frequency model that defines whether there is designed to process through several global iterations,
an intermediate stop at each half-tour. Because only one including all (or a chosen subset of) models and network
potential stop on each half tour is considered, the model assignments until an equilibrium is reached.
at the tour level has only four explicitly modeled alter- Furthermore, several important upward linkages of
natives: 1, no stops; 2, outbound stop; 3, inbound stop; the choice models through log sums from the lower-level
and 4, stops on both half tours. choices used in upper-level choices are incorporated:
Two subsequent models relate to the following trip- · Entire-tour bidirectional mode choice log sums for
level choices, which are conditional upon the previously the representative time-of-day periods (for example,
made tour-level decisions: a.m.p.m. combination for work tours and a.m.midday
combination for school tours) are used as variables in
· Stop-location model that defines a location for the primary tour destination choice models; the reason
each stop at the same level of spatial resolution as pri- that only representative mode choice log sums are used
mary destination (1,805 zones and three transit-access in the destination choice is that this choice dimension has
subzones for each zone). Stop location availability is 1,805 3 5,415 alternatives and is extremely compu-
strongly conditional on availability of the chosen tour tationally intensive.
mode and transit sub-mode to access the location; and · Entire-tour bidirectional mode choice log sums for
· Trip-mode model that defines mode and transit all time-of-day periods are used as variables in time-of-day
submode for each trip on the tour. If there is no stop on choice; because the time-of-day choice model is applied
a half tour, the entire half tour is considered one trip and conditionally upon the chosen destination, it is signifi-
the chosen mode and transit submode are preserved. If cantly less intensive computationally than destination
there is a stop, the half tour is broken into two successive choice, and it is possible to explicitly consider mode choice
trips (to and from the stop). log sums for all possible time-of-day combinations.
