I think the reasable goal for a nuclear family with small children in a mixed-transportation future is a single car household. I'm trying to get down to one car with three small children. I live in walking distance to their school, I bike to work, and my wife takes the minivan to drop the youngest to her sitter and go to her job. On weekends I take the van to take the kids to their programs while I hit the gym and then we all go shopping. My oldest sits nicely on the bus when we do that, so it's promising.