## 1 Introduction  
In the context of global urbanisation, every year more children are born and raised in urban environments, with 70% of children and youth projected to live in cities by 2050 [1]. The way urban forms are structured could influence human health and ways of living [2]. Extensive research indicates that the built environment can have an impact on population health, affecting diabetes and obesity [3], respiratory diseases [4] and cardiovascular diseases [5]. At the same time, built environments can have a preventative role in human health by promoting healthy behaviours, such as physical activity [6], healthy diet [7] and opportunities for social cohesion and restoration [8]. Despite the importance of the built environment for children's health and development [2], including potential effects on obesity and metabolic syndrome in adult life [9], less evidence exists on the influences of the built environment on children's health behaviours. More specifically, the role of the built environment in promoting healthy behaviours has been reviewed as part of the obesogenic environments [10]; although there are some urban planning initiatives to define the design principles of child-friendly cities, such as community spaces, green infrastructures that promote playing and traffic measures to prioritise pedestrians and cyclists [11; 12; 13], connections between urban forms and promotion of children's active behaviours are not yet clear. According to World Health Organisation guidelines, children and adolescents aged 5-17 should do at least an average of 60 min per day of moderate- to vigorous-intensity, mostly aerobic, physical activity across the week, in order to improve physical fitness (cardiorespiratory and muscular fitness), cardiometabolic health (blood pressure, dyslipidaemia, glucose and insulin resistance), bone health, cognitive outcomes (academic performance, executive function) and mental health (reduced symptoms of depression) and reduce adiposity ([14] (p. 1)). Physical activity typically refers to sporting and fitness activities; physical education; active play and informal activity; and transportation, including walking, cycling and wheeling [14; 15]. Active school travel (AST), both as a direct means of physical activity and as an opportunity for active play and informal activity, could be considered as a public health intervention to promote physical activity among children. AST can potentially provide an inclusive opportunity for physical activity [16] and shape life-long healthy behaviours [17]. As a means of physical activity, active travelling can benefit children's physical health [18; 19] and cognitive development [20]. Simultaneously, AST also provides an opportunity for socialising [21] and exploration of neighbourhood localities, which help create a child's identity as part of the community [22]. Similarly, AST is found to give a sense of freedom and independence to children [23], a characteristic that overlaps with the use of public spaces and parks [24]. Previous research also indicates more children would walk or cycle to school if they had the choice [25] and that children would like to have more opportunities for physical activity and engagement within open public spaces [24]. Everyday travel creates complex behaviour patterns due to modern ways of living and existing urban forms [26]. This means that promoting AST is a complex public health challenge. Previous AST models and frameworks suggest a complex relationship and dynamic interaction between individual characteristics and household, social and environmental influences on the decision-making process of school travel [27; 28; 29]. The M-CAT model suggests that apart from the household, socio-economic and cultural characteristics, the natural and built environment, as well as the perceptions of them, affect the choice of active travelling to school [28].