OTOH though, we have elementary schools in urban/suburban areas where 1/2 of the population of the school falls within the 2 mile radius (great saves money on busing!). Combined with high speed traffic, questionable neighborhoods, bad weather, a tendency towards overprotective parenting, and most parents of early elementary school children are going to be driving them rather than letting them walk to school.
The crazy thing is that most elementary schools are going to be getting out at ~3PM, which is far to early for most parents to leave their jobs, which means they end up paying a few hundred dollars a month per child in after school fees. A real problem for people near the poverty line, so those are the 5 year olds you see walking home alone at 3PM...