The Integrated Transport and Health Impact Modelling Tool for Global Cities (ITHIM-Global) was developed as an open-source tool to assess the impacts of transport mode shifts on public health and the environment in low- and middle-income countries (LMICs) where the need for such assessment is urgent and rising. The model simulates the impacts on all-cause and cause-specific mortality and years of life lost outcomes through a multi-pathway framework, specifically including physical activity, air pollution exposure, and road traffic fatalities. In addition, the model estimates changes in carbon dioxide emissions resulting from these mode shifts. ITHIM-Global employs a quasi-microsimulation approach that enables individualized exposure estimates by age, sex, and activity levels and utilises up-to-date exposure and dose-response functions that account for the non-linear relationship between physical activity levels and health. To demonstrate its functionality, document its strengths and weaknesses, and aid users, the model was applied to Bogota, Colombia, using three hypothetical scenarios, each shifting 5% of trips to one of bus, car, or cycling. Results indicate that increasing public or active transport modes enhances public health, primarily driven by gains in physical activity and to a lesser extent by reductions in traffic-related emissions. Conversely, a shift to car usage worsens health outcomes due to decreased physical activity and increased pollution exposure. ITHIM-Global serves as a flexible, detailed Health Impact Assessment (HIA) tool adaptable to urban areas across LMICs and this article delves into underlying assumptions and their influence to advance generalisable lessons on risk assessment and model development. The modular structure of ITHIM-Global, its covering of individual and population-level analyses, and extensive documentation provide an accessible, evidence-based approach for city planners and practitioners to optimize transport policies that support public health and mitigate environmental harm.

The authors have declared no competing interest.

Funding: Contributions by RG and JW were partially supported by TIGTHAT, an MRC Global Challenges Project MR/P024408/1. This project (JW, RG, LT, AA, AS, HK, DGS, CB) has received funding from the European Research Council (ERC) under the Horizon 2020 research and innovation programme (grant agreement No 817754). This material reflects only the author's views, and the Commission is not liable for any use that may be made of the information contained therein.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

We obtained essential datasets to demonstrate the implementation of ITHIM-Global in Bogota from public domains and government agencies. Population data comes from Population projections disaggregated by locality 2018-2035 based on the National Population and Housing Census 2018 (https://www.dane.gov.co/index.php/estadisticas-por-tema/demografia-y-poblacion/proyecciones-de-poblacion/proyecciones-de-poblacion-bogota), travel behaviour comes from the 2019 Mobility survey from the Integrated Information System on Regional Urban Mobility (https://www.simur.gov.co/encuestas-de-movilidad), physical activity from the 2015 Colombian National Nutrition survey from the Ministry of Health (accessible upon request), road traffic injuries from the police department shared by the Bogota Secretary of Mobility (https://datos.movilidadbogota.gov.co/search?groupIds=d3812f8315054cdc84cf744680103713), air pollution data from the 2022 version of WHO Air Quality Database (https://www.who.int/data/gho/data/themes/air-pollution/who-air-quality-database), vehicle emissions from EDGAR shared by Monica Crippa from the European Commission Joint Research Centre, and baseline mortality and years of life lost data from the Global Burden of Disease study (GBD) published by the Institute for Health Metrics and Evaluation (https://ghdx.healthdata.org/gbd-2019).