Development and Field Validation of a Universal Design–Based Maturity Index for Healthy City Governance in Thai Municipalities

Thailand’s rapid demographic aging presents significant challenges for municipal governance, particularly in ensuring accessible and inclusive urban environments. Existing Healthy City and Age-Friendly frameworks provide domain-based guidance but lack structured mechanisms for measuring institutional integration of accessibility principles. This study develops and field-validates a Universal Design–Based Maturity Index designed to assess the degree of institutional embedding of accessibility within municipal Healthy City governance. The instrument was constructed through synthesis of WHO Healthy City principles, Thailand’s national Healthy City criteria, and the WHO Age-Friendly City framework, integrated with over two decades of fieldbased Universal Design implementation experience. Content validity was assessed by five interdisciplinary experts, yielding an overall mean score of 4.85 (S-CVI/Ave ≈ 0.97). A 12-month pilot implementation in Ladsawai Municipality evaluated definitional clarity, administrative feasibility, and compatibility with planning and budgeting systems. Following refinement, the index was adopted under formal Memoranda of Understanding with five municipalities across five provinces. Findings indicate that the staged maturity ladder enables differentiation between activity-based interventions and institutional policy integration. While longitudinal outcome evaluation remains ongoing, preliminary evidence suggests cross-context applicability within decentralized governance systems. The proposed index operationalizes Universal Design as a measurable governance variable, providing municipalities with a structured pathway toward inclusive Healthy City development.