Bus transfers (access) at rapid-transit stations represent more than one-third of total boardings in large, dispersed, polycentric cities in the U.S. Yet, many station-level access-mode statistics and person-trip surveys often ommitt bus access mode or confound it with walk access. The abscence of this key statistic in official survey reports results in an incomplete understanding of multimodal interactions and may mislead planners and decision-makers in crafting effective policies geared to increase rapid-transit ridership and performance. Study of eight large transit systems and further analysis of the Los Angeles case study, with its detailed 2012 bus-rail on-board survey, were conducted to improve our understanding and planning of bus/rapid-transit interactions in polycentric cities. In order to evaluate scope, share, and impact of bus feeder routes on station boardings, the author indexed bus access events in the original survey database to estimate the number of bus transfers (access) at station-level. The socio-economic profile of riders that accessed rapid transit via bus was also rendered and trip-origin spatial distributions by access mode was also identified and tabulated. In addition, the influence of different bus feeder services (e.g. local, rapid, express) on rapid-transit station boardings was assesed in multivariate generalized linear models. Descriptive and inferential statistics results indicate that in Los Angeles, >30% of patrons are estimated to access rapid-transit via a variety of bus services; bus network connectivity is highly significant in explaining rapid transit boardings with large effects comparable to key Transit Oriented Development (TOD) factors; and notable variance in the magnitude of effects exists depending on bus service type. Station-level boarding and bus-transfers predictive equations derived from multivariate regressions such as the ones illustrated in this paper, may be used for sketch planning purposes in direct-demand models. A more nuanced, periodic, and detailed compilation of statistics related to bus transfers at station-level (as well as that of other emerging and potentially disrupting access modes) would provide a better understanding and planning of large multi-modal transit systems in the U.S. It would also bring to light an important, but under-reported, set of users.
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