Summary:

Departments of Transportation need measurement tools to (1) assess and track over time populations and geographies where mobility investments are needed, (2) assess what is driving the mobility needs of different populations and geographies so as to identify possible interventions, and (3) evaluate the impact of department investments on mobility. The Transportation Security Index (TSI) enables planners to do just this. Modeled after the Food Security Index, the TSI is a validated measure designed to capture the experience of transportation insecurity at the individual level. Informed by qualitative research, items in the TSI ask respondents to report how often in the past 30 days they have experienced a given symptom of transportation insecurity (e.g., skipping trips, not being able to leave the house). Currently, there is a validated 16-item longform TSI and a validated 6-item shortform. However, the ability of DOTs to use the TSI to assess where investments are needed and evaluate the impact of such investments on transportation insecurity is stymied by the length of the index. To increase the utility of the TSI for assessment, planning, tracking, and evaluation purposes, a shortened 3-item TSI (TSI-3) was developed and validated using data from nationally representative surveys and content expert feedback and following a similar methodology used in abbreviating the original 16-item TSI to 6-items. Results indicate that the validated TSI-3 is comparable to the TSI-6 with respect to their psychometric properties, the prevalence estimates they generate, and their predictive validity, using health outcomes. Shorter than the TSI-6 and TSI-16, the TSI-3 is more efficient and cost effective to administer. The biggest substantive difference between these measures is the categories of transportation insecurity they can identify: whereas the TSI-6 identifies three categories of insecurity (secure, marginal/low insecurity, moderate/high insecurity), the TSI-3 can only identify 2 (transportation secure/transportation insecure). This project concludes by offering several use cases for the TSI. In an appendix we detail how the TSI-3 can be implemented and point to an analysis of transportation insecurity in the City of Detroit as an illustration.

Publications:

• Final Report