Health impacts of sustainable transport policies in Sofia, Bulgaria: a microsimulation study

Urban and transport planning practices have significant impacts on health, yet health impact modelling studies remain limited in South-Eastern Europe. Sofia, as a major city in the region, faces a substantial environmental health burden, highlighting the need for healthier and more sustainable planning. The city has developed a Sustainable Urban Mobility Plan (SUMP) and recently implemented a Low Emission Zone (LEZ). This study estimates the health impacts of these policies to support their continued implementation. The modelling approach included three steps: (1) creation of an individual-level synthetic population for Sofia for 2021-2050; (2) prediction of baseline weekly travel behaviour; and (3) development of sustainable mobility scenarios. Travel behaviour was modelled using machine learning for trip generation, distance and mode choice. SUMP scenarios were built by shifting short car trips to walking, cycling, e-mobility and public transport to achieve a policy target of 50% car use reduction. The LEZ scenario assumed cleaner vehicle fleets without behavioural change. Individual exposure to physical activity and air pollution was estimated, and health impacts were modelled using a microsimulation state-transition approach. All scenarios resulted in substantial health gains, driven by reduced NO2 exposure and increased transport-related physical activity. Over 2021-2050, premature deaths decreased from 6,140 (LEZ scenario) to 12,100 (SUMP combining cycling and e-mobility). Scenarios also reduced chronic morbidity, most notably in the cycling scenario, including coronary heart disease (1,750 cases), stroke (3,510), type II diabetes (9,480), dementia (1,110) and depression (26,850 episodes). These results highlight the health relevance of sustainable transport policies in the city and provide evidence to support their implementation. The methodology also offers a transferable modelling framework that can be applied to other cities in Europe and beyond.

Key messages

• Sustainable transport policies deliver health gains, with greater benefits from behavioural change (SUMP) than from LEZ alone, which mainly reduces NO2 without increasing physical activity.

• Microsimulation provides a robust and transferable approach to estimate health impacts of urban and transport policies, supporting application in other cities.