Mapping the invisible: A population synthesis approach to perceived healthcare accessibility

Equitable transportation planning requires moving beyond objective measures of potential access to understand the realized accessibility barriers perceived by individuals. However, integrating subjective survey data into spatial policy analysis is hindered by the incompatibility between micro-level responses and macro-level administrative units. This paper presents a population synthesis approach to map these invisible barriers to healthcare. By applying Iterative Proportional Updating (IPU) to harmonized survey and census data in South Carolina, we synthesized comprehensive indices of perceived transportation barriers, including financial and time barriers, safety and security concerns, and accessibility challenges at the census tract level. The regression analysis indicates that tract-level socioeconomic vulnerabilities are more consistently associated with the three perceived transportation barrier indices and the Composite Healthcare Accessibility index than objective spatial proximity alone. Counterintuitively, urban residents often report higher financial and time burdens than their rural counterparts, complicating traditional equity narratives. A critical finding is the “quality paradox” in minority-concentrated communities, where higher pedestrian network density correlates with reduced perceived safety, suggesting that infrastructure quantity cannot substitute for environmental quality and security. These findings advocate for a paradigm shift in transport policy from generic infrastructure expansion to context-sensitive interventions. We argue that addressing healthcare access disparities requires distinct strategies which prioritize safety maintenance in urban minority neighborhoods and multi-modal connectivity in rural areas, and that synthetic population models provide the necessary granular evidence to guide these targeted investments.