The model for American walkability and density is not DC or NYC, it's places like Savannah, Charleston, New Orleans, Ashville, the feel of older streetcar suburbs and small college towns, ... None of those have subway systems, all of them are aspirational urban environments. None of them ban cars, but in all of them car traffic is slower and and more gentle. Certainly, _any_ neighborhood built before the 30s can emulate those. Later suburban developments can dial in such densification as well.
The main issue working against this is that the public realm is completely degraded because it only accommodates car traffic. Other ways of getting around are bullied out by high speed, dangerous cars. It's a textbook example of a vicious circle. The fact that there are a few urban areas in the US where owning a car is a drag due to parking issues, should not hold back meaningful improvements and efforts to break out of it anywhere else.
It's why I believe L4 self-driving is the tech that will actually reverse car dependency. If robotaxi fleets become preferred to car ownership(which would occur through the resulting economies of scale in a centralized fleet driving people to save money), the aggressive drivers stop ruling the road, replaced with polite "Three Laws" drivers; then the traffic starts downscaling because most urban trip making will work in smaller scooter or smart-car style vehicles which will benefit from continuing improvements to EV tech, and the services will optimize to cost; you'll still have the larger options available, but they appear on-demand, which makes all the difference when you're thinking about how to service a family of four. Cargo trips are already shifting in favor of autonomous delivery; two weeks ago, Wal-Mart went from testing drone delivery services to expanding them to multiple US states, and they project making 1 million deliveries this year.
So some critical threshold will occur where it becomes obvious that you have a vast unused road infrastructure, because the total urban fleet has consolidated into something that is physically smaller and literally less road-dependent, and nobody is there to prop up car ownership politically except a few enthusiasts and people living out of their cars. At that point downsizing is imminent everywhere.
It only took 20 years for cars to overtake horses in the industrialized world, and the bulk of it happened in 10. It'll happen faster this time.
The main issue working against this is that the public realm is completely degraded because it only accommodates car traffic. Other ways of getting around are bullied out by high speed, dangerous cars. It's a textbook example of a vicious circle. The fact that there are a few urban areas in the US where owning a car is a drag due to parking issues, should not hold back meaningful improvements and efforts to break out of it anywhere else.