Scholars, policymakers, and planners lack a single, valid measure of transportation insecurity. This has hindered the development of evidence on the relationship between transportation insecurity and poverty. To address this, in previous work, we developed a preliminary Transportation Security Index (TSI): a 16-item measure that captures the experience of transportation insecurity at the individual level, regardless of geography or mode of transit. In this paper, drawing on an original survey

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... a nationally representative sample (n=1,999) from GfK's KnowledgePanel®, we use confirmatory factor analysis to replicate and validate the 16-item TSI. Our results show that a slightly modified TSI16 is an effective tool that can be used to uncover transportation insecurity across different samples. They also suggest that, counter to the results of our previous study, transportation insecurity is a unidimensional condition that is experienced both materially and relationally. Together, these findings represent a significant advancement in the study and measurement of transportation insecurity.