<qa>  What is a barrier that prevents children from walking to school?Walking to school is associated with higher levels of physical activity, which is an objective of Healthy People 2010. However, parents concerns about safety have been identified as a barrier that prevents their children from walking to school. A walking school bus WSB addresses these concerns by providing a supervised period of physical activity on the way to school. A WSB is a group of children led to and from school by responsible adults who walk together along a set route. The peer-reviewed literature on active travel to school is sparse. We evaluated a WSB program, to test the hypothesis that it would increase the proportion of children walking and decrease the proportion of children driven by car to school. 