London's Ultra Low Emission Zone and active travel to school: a qualitative study exploring the experiences of children, families and teachers.

Objective: Taking a qualitative approach, we aimed to understand how London's Ultra Low Emission Zone (ULEZ) might work to change behaviour and improve health in the context of the school journey.

Design: Primary qualitative study embedded within an existing natural experimental study.

Setting: A population-level health intervention implemented across London.

Participants: Purposive sampling was used to recruit children (aged 10-11 years) from ethnically and socioeconomically diverse backgrounds within an existing cohort study, Children's Health in London and Luton.

Methods: In-person and online interviews were conducted with 21 families and seven teachers from the children's schools between November 2022 and March 2023. Verbatim transcripts were analysed drawing on Braun and Clarke's reflexive thematic analysis and guided by realist evaluation principles to identify contexts, mechanisms and outcomes using NVivo.

Results: Common context, mechanism, outcome (CMO) configurations were identified reflecting congruent narratives across children, parents and teachers, for example, current active travellers (context) reported reductions in pollution (mechanism) leading to improvements in health, including alleviated symptoms of asthma (outcome). These CMOs were broadly captured by two themes: (i) how you travelled before the ULEZ matters: the impact of travel mode on experiences of the ULEZ and (ii) your context matters: the role of socioeconomic position in experiences of the ULEZ. Participants highlighted the potential for the ULEZ to positively impact their choice of travel mode to school, experiences of the journey and their health. However, the impact of the ULEZ differed inequitably by journey length, travel mode before implementation and access to reliable and affordable public transport.

Conclusions: The capacity for the ULEZ to both narrow and exacerbate inequities across different travel contexts suggests when developing such schemes, more emphasis needs to be placed on providing accessible and affordable alternatives to driving.