Backgrouand
Active commuting to school can be a substantial opportunity to provide the necessary daily physical activity for children and to counteract childhood obesity. This paper examines the associations of urban form, in general, and street network design, in particular, with body mass index (BMI) in children aged between 12 and 16, controlling for socio-economic features (gender, educational attainment, income, and auto ownership) and daily physical activity (access mode to/from school and walking behaviour).

Methods
Data were drawn from questionnaires conducted in 20 elementary schools located in the Anatolian part of İstanbul, Turkey. Randomly selected 6th, 7th, and 8th grade students (N = 1784) completed questionnaires regarding their commuting modes to/from school while their parents (N = 1118) completed questionnaires about their socio-economic characteristics and their children's daily physical activity. Each student's BMI was calculated by measured height and weight data. Home- and school-environments (800-and 1600-m buffers around the respondent and school) were evaluated through GIS-based land-use data and segment-based street connectivity measures. Selected street segments within school-environments were also audited with regard to pedestrian environment characteristics.

Results
Findings indicate that children who actively commuted to/from school had lower BMIs than non-active commuters. More importantly, it is shown that increased street network connectivity measured at the segment-level is significantly associated with reduced BMI in school children. In fact, connectivity measures appear to be the strongest correlates of BMI.

Conclusions
This study provides important evidence for planners, urban designers, and policy makers on the significance of built environment, in general, and street network configuration, in particular, within home- and school-environments. One rule of thumb would be to design a well-connected street network with relatively denser connections and reduced direction changes within the neighbourhood – not only within a couple of blocks of homes and schools but also within their larger fabric (800–1600 mt buffers).