Fascinating and so obvious when summarised thus:
If there is a park or some kind of store within a half mile of their home, school-age youth are more than twice as likely to walk. If destinations are farther, they wait for a parental chauffeur. Think of the implications: a community with one central mega-sports complex with several baseball diamonds and soccer fields can actually be bad for children’s health if it replaces small parks scattered every few blocks.
Combine this with the tendency for lifelong exercise and eating habits to be influenced in childhood, and it's clear what the implications are.
Worth reading the whole piece: "Why Cul-de-Sacs Are Bad for Your Health"