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C O M P R E H E N S I V E E C O N O M E T R I C M I C R O S I M U L AT O R 79
5. Joint tour for the adult pursuing discretionary face components that support the saving and loading of
activity jointly with children (departure time, activity model parameters. Another type of system building
duration, travel duration, and location); block is the simulation coordinator, which controls the
6. Independent home-based tours and work-based logic and sequence in which the modeling modules are
tours for each worker in the household (number of tours; executed to generate the activity and travel patterns for a
home-stay duration before tours; tour mode; number of given household. The modules are plugged into the coor-
stops in each tour; and for each stop, activity type, activ- dinators in such a way that any module can be modified,
ity duration, travel time, and location); can have its parameters changed, and can be entirely
7. Independent home-based tours for each non- replaced by a different module without introducing
worker in the household (number of tours; home-stay changes to the rest of the system. Details on the imple-
duration before tours; tour mode; number of stops in mentation of CEMDAP Version 0.2 are available in Bhat
each tour; and for each stop, activity type, activity dura- et al. (2003).
tion, travel time, and location); and CEMDAP Version 0.3 is significantly improved over
8. Discretionary activity tours for each child in the Version 0.2 in the following ways:
household (departure time, activity duration, travel
duration, and location). 1. To accommodate the increased input database size
resulting from the more detailed zoning system, CEM-
This new modeling system enhances the previous sys- DAP now uses Postgres, rather than Microsoft Access, to
tem embedded in CEMDAP Version 0.2 in several ways. run queries about the input database. Postgres is known
First, the new system is developed at a finer spatial reso- to be stable under large data loads and is an open-source
lution and applied to a 4,874-zone system for the Dal- database software released under a Berkley Software
lasFort Worth area in Texas. Second, the activity-travel Distribution license.
patterns of children (persons under 16 years of age) are 2. The system has built-in data caching routines to
now explicitly modeled and forecast. Third, the interde- store frequently accessed data items in RAM so as to
pendencies between the travel patterns of children and reduce the number of queries and disk accesses.
their parents (such as escort to and from school and joint 3. A new model module is added to the system for
participation in discretionary activities) are explicitly jointly simulating work start and end times.
accommodated. Finally, for estimation of the models, the 4. Separate simulation coordinators are implemented
raw survey data obtained for the DallasFort Worth area to control the simulation sequence for different house-
were reprocessed to create a larger sample, and all the hold types (households with or without children, indi-
model components (over 50 in all) were reestimated. viduals who go to work, or individuals who go to
Detailed descriptions of the modeling framework, the school).
econometric structure of each model component, and 5. The system's computational efficiency is enhanced
the sequential prediction procedure are available in Guo by running the simulation over multiple threads.
et al. (2005).
PRELIMINARY SENSITIVITY TESTING
SOFTWARE IMPLEMENTATION
This section discusses preliminary sensitivity testing
The goal of the CEMDAP software development process undertaken with a recent but older version of CEMDAP.
is to provide a microsimulation platform that can be eas- Specifically, aggregate changes to the predicted activity-
ily configured for different study areas, for which the travel patterns under the following scenarios were exam-
level of data availability and, consequently, the degree of ined: 10% and 25% increases in in-vehicle travel times
modeling system complexity often vary. The software (IVTT) and 10% and 25% decreases in IVTT. The intent
design philosophy is to create a generic library of rou- of this exercise was to examine the reasonableness of
tines that form the building blocks of an activity-based predictions. Similar (but more exhaustive) tests using the
travel demand modeling system so that variants of mod- newer version of CEMDAP are planned. Further, part of
eling systems can be rapidly implemented. These build- this planned exercise will compare the outputs from
ing blocks include a number of modeling modules that CEMDAP with the outputs from the four-step modeling
are routines developed for applying different types of system currently employed by the North Central Texas
econometric models. The modeling modules can then be Council of Governments (NCTCOG).
reused and reconfigured to simulate the choice outcome The activity-travel patterns were predicted for the
of various behavioral dimensions. Configuration of the entire synthetic population (3,452,751 adults from
modules is achieved through Windows-based user inter- 1,754,674 households) for the base case and each of the
