Background <p>Geographic segmentation of health insurance creates administrative barriers that limit patients’ access to out-of-network healthcare, particularly in underserved regions. We assess the impact of a reimbursement reform removing interregional administrative barriers on patient healthcare utilization.</p> Methods <p>We conduct a quantitative quasi-experimental study using longitudinal administrative data from a representative city with limited high-tier medical resources. The causal effects of the reform are estimated based on patient visit records from January 2021 to November 2022 using a regression discontinuity of time (RDiT) design.</p> Results <p>The reform significantly increases intercity healthcare visits by up to 11.2%, especially among low-income patients and women. While patients with severe conditions benefit, increased utilization for minor ailments also occurs. This surge in demand strains medical resources, leading to increased readmission rates without reducing hospital stays.</p> Conclusions <p>Removing administrative barriers enhances equity but may reduce healthcare efficiency if demand management is neglected. Policymakers should combine expanded access with investments in local healthcare capacity and demand-side controls to ensure sustainable and equitable service delivery.</p>