Temporal variability in transit-based accessibility to supermarkets

Food desert studies attempt to identify geographic areas in which people lack access to sources of healthy food. While academic and policy research often defines access to food stores using simple Euclidean distance or road network metrics, dense urban areas with large public transit systems call for more sophisticated methods of determining access. It is particularly important to understand the level of access the transit-dependent population has to healthy food vendors, as their mobility is largely constrained by the routes and scheduling of their local public transportation system. In this study, we analyze public transit access to supermarkets in Cincinnati, Ohio. Using General Transit Feed Specification (GTFS) data from the Southwest Ohio Regional Transit Authority (SORTA) and the Transit Authority of Northern Kentucky (TANK) and custom ArcGIS tools, we calculate the time it takes to travel from each Cincinnati census block to its nearest supermarkets at different times of the day. This transit-travel-time matrix allows us to investigate food deserts that change shape based on the time of day considered and to calculate the temporal variability in block-level access. Also, by combining this time-dependent analysis with census data on race, income, and age, we search for disparities in average levels of accessibility. The results of this analysis identify the areas and subpopulations in Cincinnati with the greatest need for improved access to healthy food stores and will demonstrate how schedule-dependent transportation can be factored into measures of accessibility. Ultimately, this study paints a more complete and realistic picture of food deserts in Cincinnati and helps policy-makers better target interventions aimed at mitigating their effects.