This study aims to remedy weaknesses in current social science and urban planning scholarship on the link between transportation and social inequality. Despite the importance of transportation to individual wellbeing and opportunity, extant measures fail to precisely capture the ability to travel as needed at the individual level and are thus inadequate in generating nuanced understandings of how transportation is shaped by and shapes other forms of hardship. To overcome these limitations, we plan to develop the transportation security index, a novel measure of access to adequate transportation modeled after the food security index. We are seeking support for the second phase of development of this index: the testing of survey items that will comprise the index. We intend for this measure to eventually be used to produce national estimates of the prevalence of transportation insecurity and to improve scholarly knowledge of the role of transportation in the reproduction of social inequality through quantitative research. The generation of such knowledge is essential for designing policy solutions to address disadvantages in transportation security that are widely understood to disproportionately affect people by race, ethnicity, and other socio-demographic characteristics.