Development and validation of a 3-item transportation security index for social risk screening assessments and research into the many pathways through which transportation impacts health

Clinicians and researchers studying transportation as a social determinant of health need measurement tools that screen for people with transportation problems and reveal the pathways through which transportation impacts health. Existing versions of the Transportation Security Index (TSI), a validated measure of transportation insecurity, are lengthy, making their use in research and clinical settings difficult. In this paper, we identify and validate an abbreviated 3-item TSI. We derive the TSI-3 from its 6-item counterpart (TSI-6) by analyzing 2022 survey data representative of the U.S. population aged 25 years and older and content expert feedback. To validate the TSI-3, we embedded a split-ballot experiment in a 2024 survey with a similar sampling frame. We compared the TSI-3 and TSI-6′s psychometric properties, ability to distinguish between transportation secure and insecure people, prevalence estimates, and associations with self-rated health and major depression. Results demonstrate that the TSI-3 is an effective substitute for the TSI-6 and is faster to administer by 56%. However, whereas the TSI-6 identifies 3 categories of transportation insecurity, the TSI-3 identifies 2. For those seeking a dichotomous measure of transportation insecurity for social risk screening and research purposes, the TSI-3 is an efficient and cost-effective measure.