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OCR for page 33
22 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
The first three modules are implemented as fully dis- tours). A set of the tour frequency models is ordered and
aggregate microsimulation procedures working with linked in such a way that choices made for some pur-
individual records for the synthesized population (house- poses and household members have an impact on the
holds, persons, or tours). The last module is currently other choices of the same person as well as those of the
based on standard aggregate (zone-to-zone) assignment other household members.
algorithms built in TransCAD. The developed software The mode and destination module starts with pre-
allows for numerous feedbacks to be implemented until mode choice, in which each tour is assigned to either a
equilibrium is reached. Level-of-service skims after the motorized or a nonmotorized mode of travel. Density of
last stage can be fed back to the mode and destination nonmotorized attractions is essentially a log sum from
modules as well as to the tour-generation components the subsequent destination choice model for nonmotor-
through accessibility indices. ized travel with individual attractions available in a 3-mi
The New York Best Practices Model has the following radius around the tour origin. If the motorized option is
basic structural dimensions: chosen, then the motorized branch of the algorithm is
activated. First, the mode and primary destination choice
· Almost 4,000 traffic zones, and thus a full ori- for the entire journey is modeled (without intermediate
gindestination matrix has almost 16 million cells; stops). It can be thought of as a nested structure in which
· 11 travel modes (drive alone, shared ride-2, shared destination choice comes at the upper level of hierarchy
ride-3, shared ride-4+, transit (including bus, subway, while mode choice is placed at the lower level, condi-
and ferry) with walk access, transit with drive access, tional upon the destination choice.
commuter rail (with transit feeder lines) with walk The motorized destination choice model has been cal-
access, commuter rail with drive access, taxi, school bus ibrated by eight purposes (six original purposes with
(for journeys to school only), and walk (the only non- additional subdivision of work tours by three income
motorized mode); categories). In a microsimulation framework, the desti-
· More than 100 population slices including a com- nation choice model is applied as a doubly constrained
bination of dimensions like three household income construct (either fully constrained or relaxed
groups (low, medium, and high), four household car- constrained). Constraint of the destination ends is
sufficiency groups (without cars, cars less than a number achieved by removing the chosen (taken) attraction from
of workers, cars equal to workers, cars more than work- the zonal size variable after each individual journey sim-
ers), and three personal categories (worker, nonworking ulation. For fully constrained mandatory purposes
adult, child); (work, school, and university), an entire attraction unit
· Six travel purposes (work, school, university, is removed. For relaxedconstrained nonmandatory pur-
household maintenance, discretionary activity, and non- poses (maintenance, discretionary, and at work), only a
home-based at-work subtours); and part (0.5) of the attraction unit is removed.
· Four time-of-day periods (a.m. peak, 6:00 to The mode choice model has been calibrated by six
10:00; midday, 10:00 to 16:00; p.m. peak, 16:00 to purposes as a nested logit construct with differential
20:00; and night, 20:00 to 24:00 and 0:00 to 6:00). nesting, depending on the purpose. In most cases, drive-
alone and taxi modes proved to be in separate nests,
The tour generation module of NYBPM consists of while transit and shared-ride modes were nested in dif-
three successive models that include household popula- ferent combinations.
tion synthesizer, automobile-ownership model, and tour At the second stage of the motorized branch of the
frequency choice model. The household synthesis is algorithm, intermediate stops are modeled conditional
based on the predetermined socioeconomic controls upon the chosen mode and primary destination for the
(number of households, population, and labor force) for tour. Stops are modeled by means of two linked choice
each zone. The automobile ownership choice model is models: stop frequency and stop location. The stop loca-
applied for each household and is sensitive to the house- tion model includes a zonal stop-density size variable
hold characteristics and residential zone accessibility by that is similar to the attraction size variable. The com-
automobile and transit, respectively. The tour-frequency posite log-sum from the stop-location model is used in
model is implemented at the person level. There are three the upper-level stop-frequency model.
person types and six travel purposes that finally yield 13 The stop frequency model has been calibrated for six
tour frequency models; these take into account that chil- purposes as a multinomial logit construct. After observed
dren cannot implement journeys to work, at work, and stop frequencies from the survey were considered (it was
to the university and that nonworking adults cannot found that an absolute majority of journeys have not
implement journeys to work and at work. Each model is more than one stop on each leg, 90% to 95% depending
essentially a multinomial logit construct having three on the journey purpose), a decision was made to limit a
choice alternatives (no tours, one tour, two or more number of choice alternatives to the following four:
