You're welcome to try to Trail of Tears everybody into your preferred walled cities, but the attempt would go badly for you.
Absent that we'll need to wait for population growth (not happening, if anything we're going the other way) or immigration (ha) to fill our cities up to NYC density.
Note that NYC itself used to be even more dense than it is today. No other U.S. city is likely to reach even NYC's current density in any near- to medium-time scale.
> Absent that we'll need to wait for population growth (not happening, if anything we're going the other way) or immigration (ha) to fill our cities up to NYC density.
Nope: One need only wait for the financial collapse that is fast approaching nearly every municipality in the US due to the relative scale of infrastructure buildout + maintenance as compared to its tax base.
The "standard" American city is 100% unambiguously completely financially impossible.
This is obscured by the fact that cities traditionally account for their infrastructure as depreciating assets whose value goes to zero rather than as perpetual liabilities with exponentially increasing maintenance costs, where the expected maintenance burden of a road already far exceeds its "asset value" on day one of its creation (when it's added to the city's balance sheet as "an asset.")
The American sprawl pattern is financially impossible.
Spoiler: All of them should be this way