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

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Suggested Citation:"T57054 txt_022.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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The first three modules are implemented as fully dis- aggregate microsimulation procedures working with individual records for the synthesized population (house- holds, persons, or tours). The last module is currently based on standard aggregate (zone- to- zone) assignment algorithms built in TransCAD. The developed software allows for numerous feedbacks to be implemented until equilibrium is reached. Level- of- service skims after the last stage can be fed back to the mode and destination modules as well as to the tour- generation components through accessibility indices. The New York Best Practices Model has the following basic structural dimensions: • Almost 4,000 traffic zones, and thus a full ori- gin–destination matrix has almost 16 million cells; • 11 travel modes (drive alone, shared ride-2, shared ride-3, shared ride-4+, transit (including bus, subway, and ferry) with walk access, transit with drive access, commuter rail (with transit feeder lines) with walk access, commuter rail with drive access, taxi, school bus (for journeys to school only), and walk (the only non- motorized mode); • More than 100 population slices including a com- bination of dimensions like three household income groups (low, medium, and high), four household car- sufficiency groups (without cars, cars less than a number of workers, cars equal to workers, cars more than work- ers), and three personal categories (worker, nonworking adult, child); • Six travel purposes (work, school, university, household maintenance, discretionary activity, and non- home- based at- work subtours); and • Four time- of- day periods (a.m. peak, 6:00 to 10:00; midday, 10:00 to 16:00; p.m. peak, 16:00 to 20:00; and night, 20:00 to 24:00 and 0:00 to 6:00). The tour generation module of NYBPM consists of three successive models that include household popula- tion synthesizer, automobile- ownership model, and tour frequency choice model. The household synthesis is based on the predetermined socioeconomic controls (number of households, population, and labor force) for each zone. The automobile ownership choice model is applied for each household and is sensitive to the house- hold characteristics and residential zone accessibility by automobile and transit, respectively. The tour- frequency model is implemented at the person level. There are three person types and six travel purposes that finally yield 13 tour frequency models; these take into account that chil- dren cannot implement journeys to work, at work, and to the university and that nonworking adults cannot implement journeys to work and at work. Each model is essentially a multinomial logit construct having three choice alternatives (no tours, one tour, two or more tours). A set of the tour frequency models is ordered and linked in such a way that choices made for some pur- poses and household members have an impact on the other choices of the same person as well as those of the other household members. The mode and destination module starts with pre- mode choice, in which each tour is assigned to either a motorized or a nonmotorized mode of travel. Density of nonmotorized attractions is essentially a log sum from the subsequent destination choice model for nonmotor- ized travel with individual attractions available in a 3-mi radius around the tour origin. If the motorized option is chosen, then the motorized branch of the algorithm is activated. First, the mode and primary destination choice for the entire journey is modeled (without intermediate stops). It can be thought of as a nested structure in which destination choice comes at the upper level of hierarchy while mode choice is placed at the lower level, condi- tional upon the destination choice. The motorized destination choice model has been cal- ibrated by eight purposes (six original purposes with additional subdivision of work tours by three income categories). In a microsimulation framework, the desti- nation choice model is applied as a doubly constrained construct (either fully constrained or relaxed– constrained). Constraint of the destination ends is achieved by removing the chosen (taken) attraction from the zonal size variable after each individual journey sim- ulation. For fully constrained mandatory purposes (work, school, and university), an entire attraction unit is removed. For relaxed–constrained nonmandatory pur- poses (maintenance, discretionary, and at work), only a part (0.5) of the attraction unit is removed. The mode choice model has been calibrated by six purposes as a nested logit construct with differential nesting, depending on the purpose. In most cases, drive- alone and taxi modes proved to be in separate nests, while transit and shared- ride modes were nested in dif- ferent combinations. At the second stage of the motorized branch of the algorithm, intermediate stops are modeled conditional upon the chosen mode and primary destination for the tour. Stops are modeled by means of two linked choice models: stop frequency and stop location. The stop loca- tion model includes a zonal stop- density size variable that is similar to the attraction size variable. The com- posite log- sum from the stop- location model is used in the upper- level stop- frequency model. The stop frequency model has been calibrated for six purposes as a multinomial logit construct. After observed stop frequencies from the survey were considered (it was found that an absolute majority of journeys have not more than one stop on each leg, 90% to 95% depending on the journey purpose), a decision was made to limit a number of choice alternatives to the following four: 22 INNOVATIONS IN TRAVEL DEMAND MODELING, VOLUME 2

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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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