Why don't kids walk to school anymore?

"It's very important for parents that there be a separation or buffer between traffic and the sidewalk," she said. "They are much more willing to let their children walk when this buffer is at least eight feet wide, and when there are also trees in this area." Trees not only provide shade, but also serve as a sort of vertical barrier between sidewalk and street.

Although improving the physical environment reduces parents' concerns for their children's safety, Kweon found that the social environment---especially the likelihood of crime---strongly affects parental perceptions of safety as well. Kweon hopes to conduct a related study in Detroit to examine how the intersection of social and physical factors influences the likelihood that children will walk to school.

By identifying environmental elements conducive to walking and biking to school, Kweon hopes her research may help improve children's physical health and reduce the incidence of childhood obesity, especially prevalent among minority children.

"Walking or biking to school helps children develop an early habit of engaging in physical activity, and that can lead to a healthier and more active and healthier population," she said.

Kweon's study was supported by a grant from the U.S. Department of Transportation and from the Southwest Region University Transportation Center in College Station, Texas.

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