Maryland’s schoolchildren aren’t walking and biking to school each day because of local school policies including liability concerns, a lack of sidewalks and safe routes, according to a new survey. The Maryland Department of Transportation survey found that less than 20 percent of schools support students who walk or bike, while about the same amount of schools actively discourage them. Meanwhile the survey found that 70 percent of Prince George’s County students are bused to school, along with 69 percent in Montgomery County.