| Transit ridership is sensitive to the amount of time riders need to walk to access transit, as a small increase in walking time can have a large impact on the path utility. Therefore, an improvement in the access distance calculation should be able to provide overall improvements to a transit assignment model. The current state of practice for modeling transit access by walking uses straight line connectors from the center of transportation analysis zones, which were designed for highway demand modeling and may be too large of an area to accurately predict walking distances. Therefore, a new method is presented which models walking access along a network by using land units (e.g. blocks, parcels) without increasing computational complexity. Also, by calculating distances over a network, more realistic distances are calculated, and obstacles such as rivers or freeways are appropriately accounted for. This method was also applied to park and ride lots to assess ridership modeling improvements on a more holistic scale. This research presents a case study where a schedule based transit assignment model implements the proposed strategy on the Twin Cities network. While significant improvements in ridership accuracy were not found on a system level for walking access, lower level analysis (neighborhood) showed consistent improvements where aggregation data such as population and employment were homogeneous and present. For park and ride access, inconsistencies between scenarios were observed and the results of the application of the general access model to a more specific assignment is realized. Therefore, as each scenario performed best in different analysis, it is suggested to use the access link scenario that is most appropriate for the desired analysis. Mainly, for large scale, system level analysis the larger land use units (e.g. TAZ) can provide reasonable assignment, but for lower level analysis, such as stop level boardings or route load profiles, a more detailed scenario, such as presented in this research, should be used. |
