Road traffic modifies green space and self-rated health associations across urban England and Wales

Urban green space is increasingly linked to better public health. Natural environments in parks and woodlands may promote physical activity and prosocial behaviour, reduce stress, and restore cognition, yet modifiers of these benefits are poorly understood. Road traffic may reduce a sense of "being away" and deter activity, potentially limiting health gains. We tested whether traffic modifies green space-health associations using a novel exposure metric based on green space visibility from footpaths. In a cross-sectional ecological study of Census output areas within built-up urban areas in England, and we related the prevalence of self-rated positive (good/very good) health (2011 Census) to "experienceable" green space visible from footpaths with and without adjacent traffic. Non-linear spline models adjusted for age, sex, and area-level confounders showed strong positive associations for trees outside woodland visible from roadside footpaths with traffic and for woodland visible from footpaths without traffic. Associations for ground cover adjacent to footpaths were generally positive but smaller. By contrast, woodland adjacent to footpaths with traffic showed a negative association. The findings support provision of woodland experiences away from traffic while also suggesting benefits of roadside tree planting.