Background The benefits of physical activity have been extensively documented and recognised. In addition to that, numerous studies have demonstrated a clear link between active travel and increased physical activity levels in young people. Active travel also has the potential to reduce air pollution by reducing motorised transport use. The promotion of active travel to school to enhance young people's physical activity and reduce air pollution can be harnessed globally, yet limited evidence exists specifically for Asia.

Aim This thesis aims to assess the current state of active travel in young people in Asia, study its associations with physical activity and environmental factors, and explore how it is discussed in urban- related policies.

Study 1 I first investigated the association between school travel modes and physical activity levels among young people in Asia. I used an accelerometer-assessed physical activity data from 1,052 6 to 7-year-old school children from Guangzhou, China, to show that individuals who engage in active travel to school accumulate more minutes of moderate to vigorous physical activity overall. The difference ranged from 8% to 16% in average daily minutes of MVPA.

Study 2 In the subsequent analysis, I utilised data from 152,368 adolescents aged 13 to 17 years old from 31 Asian countries included in the Global School-based Student Health Survey to investigate the prevalence of active travel to school among adolescents in Asia. The findings showed that 55% of the adolescents in Asia regularly walk or cycle to school, with large variations observed across countries (e.g., 18% in the United Arab Emirates to 84% in Myanmar). Overall, older and male adolescents, and adolescents with underweight and normal BMI category are more likely to actively travel to school.

Study 3 To investigate what could be driving the between countries variation, in my third study, I examined the association between the prevalence of active travel to school and country-level social and physical environmental correlates in Asia. This study showed that Asian countries with a greater number of people living in urban areas, lower levels of overall adult physical activity and higher levels of night-time light have a lower prevalence of adolescent active travel to school. Country-level physical and social environmental correlates explained some of the regional variance in active travel to school.

Study 4 In the last study, I conducted a document analysis to explore the ways in which young people’s active travel is considered in National Urban Policy (NUP) documents in selected Asian countries and to identify opportunities for supporting the improvement of young people’s active travel in Asia. I applied thematic coding on NUP documents from 15 Asian countries available on the UN-Habitat’s Urban Policy Platform website. The findings showed that countries’ national urban policies in Asia overlooked the opportunity to promote physical activity in young people through active travel and that the link between active travel within the transport context and health is nearly non-existent in these NUP documents.

Conclusions This thesis provides an understanding of young people’s active travel in Asia and its associations with physical activity, environmental correlates and urban policy. Engaging in active travel to school contributes to more physical activity overall. However, only half of the adolescents in Asia are engaging in active travel to school, with differences between countries driven partially by environmental correlates. National urban policies in Asia overlooked the opportunity to promote physical activity in young people through active travel.