Background
Active Travel to School (ATS) (e.g., walking or bicycling to school) can help increase children’s physical activity levels [1]. A growing body of literature has identified environmental correlates of ATS leading to active discussions on relevant intervention strategies [2-4]. Home-to-school distance is one of the most influential factors determining the likelihood of choosing an active travel mode. However, the distance variable in previous studies has been used primarily as one of the independent or control variables predicting the rates/odds of ATS. Potential differences in the roles that the built and natural environmental variables may have on ATS by different home-to-school distance ranges have not been explored sufficiently.

Objectives
This study examines the built and natural environmental correlates of ATS separately at four distance ranges: 1.5 miles. One mile has been generally reported as an acceptable maximum distance for walking or bicycling to school [5], and therefore this study uses 1 mile and 1±0.5 miles as the thresholds to divide up the distance ranges.

Methods
This cross-sectional study utilized the secondary survey data derived from a research project (2008-11) funded by the Robert Wood Johnson Foundation’s Active Living Research Program. A total of 4,602 parents whose children were enrolled in 20 public elementary schools in the Austin Independent School District in Austin, Texas, participated in the surveys. The survey variables including child’s gender, grade, language spoken at home, parent’s car ownership, and parental education levels were used as confounders for this study. The main outcome variable, also derived from the survey, was a dummy variable indicating whether the child walked or biked to/from school on a normal day. The built and natural environmental variables were measured objectively utilizing Geographic Information Systems (GIS) techniques and remote sensing software, Environment for Visualizing Images, within 100 feet home-to-school route buffers. The shortest home-to-school routes were calculated in GIS based on the geocoded home and school addresses. The built environmental variables captured transportation infrastructure (sidewalks, bike lanes, highways, etc.), land uses, and crime and crash incidences, within the buffer. For the natural environments, park presence, land cover types, greenness measured by a Normalized Difference Vegetation Index (NDVI), temperature, and tree height variables were included. Mixed-effects logistic regression models were estimated separately for each of the four distance ranges.

Results
Results from the regression models demonstrated that the relationships between the environmental variables and ATS varied by home-to-school distance ranges. Among the personal factors, higher grades and using Spanish (vs. English) at home were positively associated with ATS at the two shortest ranges only; and more cars in the household and higher parental education levels were negatively associated with ATS in all but the longest range.   Regarding the environmental correlates of ATS, shorter home-to-school distances (continuous variable) were associated with increased odds of walking/bicycling to school at the two shorter distance ranges only. Other significant environmental correlates of ATS across the distance ranges included: (1) the percentage of sidewalks, positive at the 1-1.5 miles range only, (2) the presence of bike lanes, positive at 0.5-0.99 and 1-1.5 miles, (3) the presence of playgrounds, positive at 1.5 miles.

Conclusions
Except for a few studies conducted outside the US [3, 4], this study is one of the first US studies to examine the potentially different roles of the environmental factors in promoting or hindering ATS by different home-to-school distance ranges. This study found that children’s ATS in the shorter, walkable distance ranges were shown to have strong associations with both personal factors such as child’s grade, language, and car ownership, and the built environmental features such as playgrounds, parks, bike lanes, and crash-safety en route to school. However, from the longer distance ranges, no personal factors were found significant, and only a small number of environmental correlates were found significant, including two natural (steep slopes, and tree canopies) and one built (highways) environmental variables.

Implications
This study showed that ATS intervention strategies targeting the built environment may be more effective at shorter distance ranges. Provision of playgrounds and parks, and improvement of crash-related safety near schools can help encourage ATS. Providing shade trees and avoiding hilly terrains en route to school may help longer-distance commuters to consider active modes. However, a more realistic intervention recommendation for longer-distance commuters would be to promote the school bus use, instead of walking or bicycling, as a more feasible alternative to driving, and to revisit the current school bus eligibility policy (e.g. changing from 2+ miles to 1−1.5+ miles in case of Austin).

References

1. Faulkner, G. E. J., Buliung, R., Flora, P., & Fusco, C. (2009). Active school transport, physical activity levels and body weight of children and youth: A systematic review. Preventive Medicine, 48(1), 3-8.
2. Davison, K. K., Werder, J. L., & Lawson, C. T. (2008). Children’s active commuting to school: Current knowledge and future directions. Prev Chronic Dis, 5, A100.
3. Panter, J. R., Jones, A. P.,  Van Sluijs, E. M., & Griffin S. J. (2010). Attitudes, social support and environmental perceptions as predictors of active commuting behaviour in school children. Journal of Epidemiology and Community Health, 64, 41-48.
4. Panter, J. R., Jones, A. P., Van Sluijs, E. M. & Griffin, S. J. (2010). Neighborhood, route, and school environments and children's active commuting. American Journal of Preventive Medicine, 38, 268-278.
5. McDonald, N. C., Brown, A. L., Marchetti, L. M. & Pedroso, M. S. (2011). U.S. school travel, 2009: An assessment of trends. American Journal of Preventive Medicine, 41, 146-151.

Support / Funding Source
This study was supported by a Robert Wood Johnson Foundation’s Active Living Research Grant (Grant ID: 65539).