Utilizing aggregate transit demand with dynamic transit assignment models : a guide for metropolitan planning organizations
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Activity based models and dynamic traffic assignment models have begun to emerge in the transportation planning industry as an alternative method to the traditional four-step model by more realistically representing trip tours on a finer time scale and depicting the effects of time-dependent traffic flow throughout the network. A barrier, however, for many MPOs across the country to developing ABMs and DTA models is the immense amount of resources required to produce and validate a complete network. Having the capability of using trip tables produced using the four-step model allows MPOs to benefit from the advantages of using a dynamic model while accepting some inaccuracies due to inherent incompatibilities between model methodologies. DTA models have predominately lacked the ability to represent transit apart from pre-specified dwell times, yet current initiatives are focused on developing FAST-TrIPs as a dynamic transit assignment model capable of integrating with DTA software packages to better account for variations in transit ridership. This thesis seeks to act as a guide for MPOs looking to implement existing transit trip tables from a four-step model in conjunction with FAST-TrIPs dynamic transit assignment software to analyze the affects of transit vehicle congestion and schedule reliability at the passenger level. Due to innate assumptions made when modeling transit in the four-step model such as transit schedule and accessibility, modelers must take particular care in characterizing inputs for the dynamic model. Proposals are made related to developing the transit network, processing transit demand, and creating configuration settings for the model. A case study set in Austin, TX uses the regional transit network and transit demand to emphasize particular inputs that are susceptible to causing passengers to go unassigned due to the inconsistency of the models while suggesting opportunities to limit such issues. Due to the high variability in current four-step model structures, the goal of this thesis provides readers with the proper knowledge necessary to develop unique processes applicable to their own region.