Walk. Bicycle. Use public transit. In extremity, buy an electric car (but that has issues, too).
If your question is "what should people who live, heavily subsidized, in suburbs and exurbs, do?", then the answer teases itself out pretty elegantly.
I agree you could do a lot of hiking or road trips and fit within that footprint.
Most people? Sure. It requires re-thinking how we (Americans particularly) structure our cities, and will not be an overnight process, but what is preventing us from doing this generally? Aside from the idea that such re-thinking is impossible, anyway.
The fact that people don't actually want to do that? People are free to live their lives the way they want. There's no reason to pile most people into cities just "because cars"
Or, put more bluntly: why must I and my children pay for them?
Because uh. That's literally sociopathic.
So if you suggest all people living in the countryside should move into cities, you are also taking about a huge economic undertaking that would also produce huge amounts of CO2.
Presumably some people are also needed in the countryside, to do the farming, and support the farmers.
Subsidizing suburbs is of course stupid. But simply rolling everything back is not really feasible.
Even in the past when people moved to the suburbs, presumably they did so because living in the city would have been prohibitively expensive.
https://en.m.wikipedia.org/wiki/White_flight
Cities used to be inexpensive. Not cheap, but not crushing. (We made them less so by letting up on the development of housing.)
Is that seriously your world view? I think then you are too eager to swallow simplistic explanations.
And even if "white flight" were the determining factor, it would be another step to claim the goal was "racial homogeneity". People might simply have wanted to move into nicer neighborhoods. (see checkerboard experiment, described in you linked Wikipedia article). White people might have been more likely to be wealthy enough to afford the "flight" (wasn't that what rich people always did throughout the centuries). Even if they were more wealthy because of racism (which would in itself be worthy of debate), it doesn't imply their flight was driven by desire for racial homogeneity.
I live in a country where such race relations are not an issue, and people moved to the countryside here, too. It was also subsidized or used to be subsidized, for various reasons. Also simply mass availability of cars might have been a factor. Remember, cars were not available to everybody for most of human history.
Cities being inexpensive - a lot of factors play into it, probably. Pollution could have made them unattractive and therefore cheap, in the early days of industrialization. One example. Housing restrictions - OK, but also more people moving there. Better job availability. And so on. Your world view is too simplistic imo.