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Innovations in Travel Demand Modeling, Volume 2: Papers (2008)

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Suggested Citation:"T57054 txt_079.pdf." National Academies of Sciences, Engineering, and Medicine. 2008. Innovations in Travel Demand Modeling, Volume 2: Papers. Washington, DC: The National Academies Press. doi: 10.17226/13678.
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5. Joint tour for the adult pursuing discretionary activity jointly with children (departure time, activity duration, travel duration, and location); 6. Independent home- based tours and work- based tours for each worker in the household (number of tours; home- stay duration before tours; tour mode; number of stops in each tour; and for each stop, activity type, activ- ity duration, travel time, and location); 7. Independent home- based tours for each non- worker in the household (number of tours; home- stay duration before tours; tour mode; number of stops in each tour; and for each stop, activity type, activity dura- tion, travel time, and location); and 8. Discretionary activity tours for each child in the household (departure time, activity duration, travel duration, and location). This new modeling system enhances the previous sys- tem embedded in CEMDAP Version 0.2 in several ways. First, the new system is developed at a finer spatial reso- lution and applied to a 4,874-zone system for the Dal- las–Fort Worth area in Texas. Second, the activity- travel patterns of children (persons under 16 years of age) are now explicitly modeled and forecast. Third, the interde- pendencies between the travel patterns of children and their parents (such as escort to and from school and joint participation in discretionary activities) are explicitly accommodated. Finally, for estimation of the models, the raw survey data obtained for the Dallas–Fort Worth area were reprocessed to create a larger sample, and all the model components (over 50 in all) were reestimated. Detailed descriptions of the modeling framework, the econometric structure of each model component, and the sequential prediction procedure are available in Guo et al. (2005). SOFTWARE IMPLEMENTATION The goal of the CEMDAP software development process is to provide a microsimulation platform that can be eas- ily configured for different study areas, for which the level of data availability and, consequently, the degree of modeling system complexity often vary. The software design philosophy is to create a generic library of rou- tines that form the building blocks of an activity- based travel demand modeling system so that variants of mod- eling systems can be rapidly implemented. These build- ing blocks include a number of modeling modules that are routines developed for applying different types of econometric models. The modeling modules can then be reused and reconfigured to simulate the choice outcome of various behavioral dimensions. Configuration of the modules is achieved through Windows- based user inter- face components that support the saving and loading of model parameters. Another type of system building block is the simulation coordinator, which controls the logic and sequence in which the modeling modules are executed to generate the activity and travel patterns for a given household. The modules are plugged into the coor- dinators in such a way that any module can be modified, can have its parameters changed, and can be entirely replaced by a different module without introducing changes to the rest of the system. Details on the imple- mentation of CEMDAP Version 0.2 are available in Bhat et al. (2003). CEMDAP Version 0.3 is significantly improved over Version 0.2 in the following ways: 1. To accommodate the increased input database size resulting from the more detailed zoning system, CEM- DAP now uses Postgres, rather than Microsoft Access, to run queries about the input database. Postgres is known to be stable under large data loads and is an open- source database software released under a Berkley Software Distribution license. 2. The system has built- in data caching routines to store frequently accessed data items in RAM so as to reduce the number of queries and disk accesses. 3. A new model module is added to the system for jointly simulating work start and end times. 4. Separate simulation coordinators are implemented to control the simulation sequence for different house- hold types (households with or without children, indi- viduals who go to work, or individuals who go to school). 5. The system’s computational efficiency is enhanced by running the simulation over multiple threads. PRELIMINARY SENSITIVITY TESTING This section discusses preliminary sensitivity testing undertaken with a recent but older version of CEMDAP. Specifically, aggregate changes to the predicted activity- travel patterns under the following scenarios were exam- ined: 10% and 25% increases in in- vehicle travel times (IVTT) and 10% and 25% decreases in IVTT. The intent of this exercise was to examine the reasonableness of predictions. Similar (but more exhaustive) tests using the newer version of CEMDAP are planned. Further, part of this planned exercise will compare the outputs from CEMDAP with the outputs from the four- step modeling system currently employed by the North Central Texas Council of Governments (NCTCOG). The activity- travel patterns were predicted for the entire synthetic population (3,452,751 adults from 1,754,674 households) for the base case and each of the 79COMPREHENSIVE ECONOMETRIC MICROSIMULATOR

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TRB Conference Proceedings 42, Innovations in Travel Demand Modeling, Volume 2: Papers includes the papers that were presented at a May 21-23, 2006, conference that examined advances in travel demand modeling, explored the opportunities and the challenges associated with the implementation of advanced travel models, and reviewed the skills and training necessary to apply new modeling techniques. TRB Conference Proceedings 42, Innovations in Travel Demand Modeling, Volume 1: Session Summaries is available online.

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