Yes, that entire 80% can be – and needs to be – made walkable. That’s because the suburbs are unsustainable ponzi schemes that were fundamentally built wrong. Anything less dense than, say, a streetcar suburb (about 10 houses/acre) is a lost cause that we need to raze and start over.

I’m not saying that because I’m making some moral judgement about suburbanites’ lifestyle, by the way. I’m saying it because, with such an excessive amount of street frontage per dwelling unit, car-dependent, large-lot suburbs simply cost more in infrastructure upkeep than they generate in taxes. Whether the town goes bankrupt trying to subsidize them or it raises the taxes to cover the costs and the homeowners get foreclosed on, all but the richest of them are financially doomed in the long run.

When I say that cities “need” to become walkable, I say it in the same sense that people “need” food and water. It isn’t a choice.

That’s literally the whole problem the thread you’re replying to started with. The way land is wasted for cars. Stop thinking about whether or not it is possible to replace cars. What needs to change is that we build a world around cars that cannot sustain itself.