Residential mobility rates in the U.S. have been in steady decline. Most notably, between 2005 and 2013, one-year intercity migration rate for immigrants has decreased by 0.7 percentage-points, compared to a 0.2 percentage-point decline for the U.S.-born population. Literature on urban implications of geographic mobility suggests that consideration of migration trends, or population flows, can improve urban planning, including transportation. Our research focuses on recent immigrants, a group that significantly contributes to public transit ridership in the U.S. In this study, we analyze the influence of the annual average in-migration rate of recent immigrants to various urban areas from within the country on transit ridership changes across the urban areas between 2008 and 2013. We also compare this effect with the effect of annual average in-migration rate of new immigrants to various urban areas from foreign countries. While the average effect of inflow of new foreign migrants on transit demand is suggested in the literature, distinguishing the transit demand of immigrants that are not movers and those that are movers from various locations remains unexplored.
We derive migration flows from the American Community Survey microdata, and transit ridership from the U.S. National Transit Database. We perform geospatial analysis to overcome several constraints that make exploration of the migration-transportation connection difficult, particularly the lack of uniformity in geographic boundaries used for data presentation across and within government agencies, and over time.
Our results indicate that consideration of domestic in-migration rates of recent immigrants can improve transit demand forecasting. As past literature has found, recent immigrants are highly likely to use transit. Recent immigrant migrants that have arrived directly from another country are even more likely to use transit. Interestingly, recent immigrants that move to a metropolitan area from another location in the U.S. are relatively less likely to use transit. Among domestic migrants, however, those that move to cities undergoing large increase in transit service relative to population are more likely to use transit. High population and transit stop density of both previous and current cities seem to positively affect transit mode choice for commute trips of recent immigrant movers. Declining inter-urban mobility among recent immigrants can indeed alter future transit demand trends. Transit agencies should not treat recent immigrants as a monolithic group. Consideration of the migration patterns of various types of recent immigrants, and factors that determine those patterns, can improve demand forecasting and planning.
